SVM100-A
December 1995
SQUARE WAVE TIG 255
For use with machine Code Numbers
For use with machine Code Numbers
For use with machine Code Numbers
For use with machine Code Numbers
For use with machine Code Numbers
For use with machine Code Numbers
10022
10023
10024
10025
10026
10134
Safety Depends on You
Lincoln arc welding and cutting
equipment is designed and built
with safety in mind. However, your
overall safety can be increased by
proper installation ... and thought-
ful operation on your part. DO
NOT INSTALL, OPERATE OR
REPAIR THIS EQUIPMENT
WITHOUT READING THIS
MANUAL AND THE SAFETY
PRECAUTIONS CONTAINED
THROUGHOUT. And, most
importantly, think before you act
and be careful.
SERVICE MANUAL
World's Leader in Welding and Cutting Products
Premier Manufacturer of Industrial Motors
Sales and Service through Subsidiaries and Distributors Worldwide
22801 St. Clair Ave. Cleveland, Ohio 44117-1199 U.S.A. Tel. (216) 481-8100
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ii
SAFETY
WELDING SPARKS can
cause fire or explosion.
CYLINDER may explode
if damaged.
4.a. Remove fire hazards from the welding area.
If this is not possible, cover them to prevent
5.a. Use only compressed gas cylinders
containing the correct shielding gas for the
the welding sparks from starting a fire.
Remember that welding sparks and hot
materials from welding can easily go through small cracks
and openings to adjacent areas. Avoid welding near
hydraulic lines. Have a fire extinguisher readily available.
process used and properly operating
regulators designed for the gas and
pressure used. All hoses, fittings, etc. should be suitable for
the application and maintained in good condition.
5.b. Always keep cylinders in an upright position securely
chained to an undercarriage or fixed support.
4.b. Where compressed gases are to be used at the job site,
special precautions should be used to prevent hazardous
situations. Refer to “Safety in Welding and Cutting” (ANSI
Standard Z49.1) and the operating information for the
equipment being used.
5.c. Cylinders should be located:
•Away from areas where they may be struck or subjected to
physical damage.
4.c. When not welding, make certain no part of the electrode
circuit is touching the work or ground. Accidental contact
can cause overheating and create a fire hazard.
•A safe distance from arc welding or cutting operations and
any other source of heat, sparks, or flame.
5.d. Never allow the electrode, electrode holder or any other
electrically “hot” parts to touch a cylinder.
4.d. Do not heat, cut or weld tanks, drums or containers until the
proper steps have been taken to insure that such procedures
will not cause flammable or toxic vapors from substances
inside. They can cause an explosion even though they have
been “cleaned”. For information, purchase “Recommended
Safe Practices for the Preparation for Welding and Cutting of
Containers and Piping That Have Held Hazardous
Substances”, AWS F4.1 from the American Welding Society
(see address above).
5.e. Keep your head and face away from the cylinder valve outlet
when opening the cylinder valve.
5.f. Valve protection caps should always be in place and hand
tight except when the cylinder is in use or connected for
use.
5.g. Read and follow the instructions on compressed gas
cylinders, associated equipment, and CGA publication P-l,
“Precautions for Safe Handling of Compressed Gases in
Cylinders,” available from the Compressed Gas Association
1235 Jefferson Davis Highway, Arlington, VA 22202.
4.e. Vent hollow castings or containers before heating, cutting or
welding. They may explode.
4.f. Sparks and spatter are thrown from the welding arc. Wear oil
free protective garments such as leather gloves, heavy shirt,
cuffless trousers, high shoes and a cap over your hair. Wear
ear plugs when welding out of position or in confined places.
Always wear safety glasses with side shields when in a
welding area.
FOR ELECTRICALLY
powered equipment.
6.a. Turn off input power using the disconnect
switch at the fuse box before working on
the equipment.
4.g. Connect the work cable to the work as close to the welding
area as practical. Work cables connected to the building
framework or other locations away from the welding area
increase the possibility of the welding current passing
through lifting chains, crane cables or other alternate cir-
cuits. This can create fire hazards or overheat lifting chains
or cables until they fail.
6.b. Install equipment in accordance with the U.S. National
Electrical Code, all local codes and the manufacturer’s
recommendations.
6.c. Ground the equipment in accordance with the U.S. National
Electrical Code and the manufacturer’s recommendations.
4.h. Also see item 7c.
Mar. ‘93
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iii
SAFETY
ELECTRIC AND MAGNETIC
FIELDS
may be dangerous
FOR ENGINE
powered equipment.
7.a. Turn the engine off before troubleshooting and maintenance
work unless the maintenance work requires it to be running.
____________________________________________________
8.a. Electric current flowing through any conductor causes
localized Electric and Magnetic Fields (EMF). Welding
current creates EMF fields around welding cables and
welding machines
7.b. Operate engines in open, well-ventilated
areas or vent the engine exhaust fumes
outdoors.
8.b. EMF fields may interfere with some pacemakers, and
welders having a pacemaker should consult their physician
before welding.
____________________________________________________
8.c. Exposure to EMF fields in welding may have other health
effects which are now not known.
7.c. Do not add the fuel near an open flame
welding arc or when the engine is running.
Stop the engine and allow it to cool before
refueling to prevent spilled fuel from
vaporizing on contact with hot engine parts
and igniting. Do not spill fuel when filling
tank. If fuel is spilled, wipe it up and do not
start engine until fumes have been
eliminated.
8d. All welders should use the following procedures in order to
minimize exposure to EMF fields from the welding circuit:
8.d.1. Route the electrode and work cables together - Secure
them with tape when possible.
8.d.2. Never coil the electrode lead around your body.
8.d.3. Do not place your body between the electrode and
work cables. If the electrode cable is on your right
____________________________________________________
side, the work cable should also be on your right side.
7.d. Keep all equipment safety guards, covers
and devices in position and in good repair.
Keep hands, hair, clothing and tools away
from V-belts, gears, fans and all other
moving parts when starting, operating or
repairing equipment.
8.d.4. Connect the work cable to the workpiece as close as
possible to the area being welded.
8.d.5. Do not work next to welding power source.
Mar. ‘93
____________________________________________________
7.e. In some cases it may be necessary to remove safety
guards to perform required maintenance. Remove
guards only when necessary and replace them when the
maintenance requiring their removal is complete.
Always use the greatest care when working near moving
parts.
7.f. Do not put your hands near the engine fan. Do not
attempt to override the governor or idler by pushing on
the throttle control rods while the engine is running.
7.g. To prevent accidentally starting gasoline engines while
turning the engine or welding generator during maintenance
work, disconnect the spark plug wires, distributor cap or
magneto wire as appropriate.
___________________________________________________
7.h. To avoid scalding, do not remove the
radiator pressure cap when the engine is
hot.
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iv
SAFETY
5. Toujours porter des lunettes de sécurité dans la zone de
PRÉCAUTIONS DE SÛRETÉ
soudage. Utiliser des lunettes avec écrans lateraux dans les
zones où l’on pique le laitier.
Pour votre propre protection lire et observer toutes les instruc-
tions et les précautions de sûreté specifiques qui parraissent
dans ce manuel aussi bien que les précautions de sûreté
générales suivantes:
6. Eloigner les matériaux inflammables ou les recouvrir afin de
prévenir tout risque d’incendie dû aux étincelles.
7. Quand on ne soude pas, poser la pince à une endroit isolé de
la masse. Un court-circuit accidental peut provoquer un
échauffement et un risque d’incendie.
Sûreté Pour Soudage A L’Arc
1. Protegez-vous contre la secousse électrique:
a. Les circuits à l’électrode et à la piéce sont sous tension
quand la machine à souder est en marche. Eviter toujours
tout contact entre les parties sous tension et la peau nue
ou les vétements mouillés. Porter des gants secs et sans
trous pour isoler les mains.
8. S’assurer que la masse est connectée le plus prés possible
de la zone de travail qu’il est pratique de le faire. Si on place
la masse sur la charpente de la construction ou d’autres
endroits éloignés de la zone de travail, on augmente le risque
de voir passer le courant de soudage par les chaines de lev-
age, câbles de grue, ou autres circuits. Cela peut provoquer
des risques d’incendie ou d’echauffement des chaines et des
câbles jusqu’à ce qu’ils se rompent.
b. Faire trés attention de bien s’isoler de la masse quand on
soude dans des endroits humides, ou sur un plancher
metallique ou des grilles metalliques, principalement dans
les positions assis ou couché pour lesquelles une
grande partie du corps peut être en contact avec la
masse.
9. Assurer une ventilation suffisante dans la zone de soudage.
Ceci est particuliérement important pour le soudage de tôles
galvanisées plombées, ou cadmiées ou tout autre métal qui
produit des fumeés toxiques.
c. Maintenir le porte-électrode, la pince de masse, le câble
de soudage et la machine à souder en bon et sûr état
defonctionnement.
d.Ne jamais plonger le porte-électrode dans l’eau pour le
refroidir.
10. Ne pas souder en présence de vapeurs de chlore provenant
d’opérations de dégraissage, nettoyage ou pistolage. La
chaleur ou les rayons de l’arc peuvent réagir avec les
vapeurs du solvant pour produire du phosgéne (gas forte-
ment toxique) ou autres produits irritants.
e. Ne jamais toucher simultanément les parties sous tension
des porte-électrodes connectés à deux machines à soud-
er parce que la tension entre les deux pinces peut être le
total de la tension à vide des deux machines.
f. Si on utilise la machine à souder comme une source de
courant pour soudage semi-automatique, ces precautions
pour le porte-électrode s’applicuent aussi au pistolet de
soudage.
11. Pour obtenir de plus amples renseignements sur la sûreté,
voir le code “Code for safety in welding and cutting” CSA
Standard W 117.2-1974.
2. Dans le cas de travail au dessus du niveau du sol, se pro-
téger contre les chutes dans le cas ou on recoit un choc. Ne
jamais enrouler le câble-électrode autour de n’importe quelle
partie du corps.
PRÉCAUTIONS DE SÛRETÉ POUR
LES MACHINES À SOUDER À
TRANSFORMATEUR ET À
REDRESSEUR
3. Un coup d’arc peut être plus sévère qu’un coup de soliel,
donc:
a. Utiliser un bon masque avec un verre filtrant approprié
ainsi qu’un verre blanc afin de se protéger les yeux du
rayonnement de l’arc et des projections quand on soude
ou quand on regarde l’arc.
1. Relier à la terre le chassis du poste conformement au code
de l’électricité et aux recommendations du fabricant. Le dis-
positif de montage ou la piece à souder doit être branché à
une bonne mise à la terre.
b. Porter des vêtements convenables afin de protéger la
peau de soudeur et des aides contre le rayonnement de
l‘arc.
c. Protéger l’autre personnel travaillant à proximité au
soudage à l’aide d’écrans appropriés et non-inflamma-
bles.
2. Autant que possible, I’installation et l’entretien du poste
seront effectués par un électricien qualifié.
3. Avant de faires des travaux à l’interieur de poste, la
debrancher à l’interrupteur à la boite de fusibles.
4. Des gouttes de laitier en fusion sont émises de l’arc de
soudage. Se protéger avec des vêtements de protection
libres de l’huile, tels que les gants en cuir, chemise épaisse,
pantalons sans revers, et chaussures montantes.
4. Garder tous les couvercles et dispositifs de sûreté à leur
place.
Mar. ‘93
SQUARE WAVE TIG 255
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v
MASTER TABLE OF CONTENTS FOR ALL SECTIONS
Page
Safety .........................................................................................................................i-iv
Installation ......................................................................................................Section A
Technical Specifications ........................................................................................A-1
Location .................................................................................................................A-2
High Frequency Interference Protection................................................................A-2
Input Connections..................................................................................................A-3
Output Connections...............................................................................................A-4
Operation .........................................................................................................Section B
Safety Precautions.................................................................................................B-1
Graphic Symbols..........................................................................................B-2 – B-3
General Description...............................................................................................B-4
Design Features and Advantages .........................................................................B-4
Welding Capability.................................................................................................B-5
Limitations..............................................................................................................B-5
Controls and Settings ............................................................................................B-6
Hand and Foot Amptrol Operation.........................................................................B-8
Welding Operation .....................................................................................B-8 – B-11
Auxillary Power....................................................................................................B-11
Overload Protection.............................................................................................B-12
Accessories.....................................................................................................Section C
Maintenance ....................................................................................................Section D
Safety Precautions ................................................................................................D-1
Routine and Periodic Maintenance........................................................................D-1
General Assembly Exploded View ........................................................................D-2
Theory of Operation........................................................................................Section E
Power Supply Operation ...............................................................................E1 – E-5
SCR Operation ......................................................................................................E-6
Thermal Protection ................................................................................................E-7
Troubleshooting and Repair...........................................................................Section F
How To Use Troubleshooting Guide......................................................................F-1
PC Board Troubleshooting Procedures .................................................................F-2
Troubleshooting Guide ...............................................................................F-3 – F-15
Test Procedures .......................................................................................F-17 – F-28
Oscilloscope Waveforms..........................................................................F-31 – F-39
Replacement Procedures.........................................................................F-40 – F-42
Re-Test After Repair............................................................................................F-44
Electrical Diagrams.........................................................................................Section G
Parts Manual..........................................................................................................P-241
SQUARE WAVE TIG 255
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Section A
TABLE OF CONTENTS
- INSTALLATION SECTION -
Installation .......................................................................................................Section A
Technical Specifications ........................................................................................A-1
Input and Output Specifications
Cable and Fuse Sizes
Physical Dimensions
Location .................................................................................................................A-2
Stacking ..........................................................................................................A-2
Tilting...............................................................................................................A-2
High Frequency Interference Protection................................................................A-2
Input Connections..................................................................................................A-3
Reconnect Procedure............................................................................................A-4
Output Connections...............................................................................................A-4
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A-1
INSTALLATION
TECHNICAL SPECIFICATIONS – SQUARE WAVE TIG 255
INPUT - SINGLE PHASE ONLY
Standard
Voltage
Input Current at
Rated Output (1)
81/74/37
Code
Number
10022
10023
10024
10025
10026
10134
208/230/460/1/60
230/460/575/1/60
200/240/400/1/50/60
220/380/440/1/50/60
380/415/500/1/50/60
220/380/415/1/50/60
74/37/30
85/77/44
77/45/39
45/41/33
77/45/41
RATED OUTPUT
Duty Cycle
40% Duty Cycle
NEMA Class II (40)
60% Duty Cycle
100% Duty Cycle
Amps
255
Volts at Rated Amperes
30
200
150
28
26
OUTPUT
Welding Current Range
(Continuous)
Constant Open
Circuit Voltage
Stick OCV: 76
TIG OCV: 53
Auxiliary Power
115 Volts AC, 10 Amps
5-315 Amps
AC and DC
220Volts AC, 2 Amps
(50/60 Hz. machines only)
RECOMMENDED INPUT WIRE AND FUSE SIZES
For all Stick, DC TIG, and Balanced AC TIG
Welding at 255A/30V/40% Duty Cycle
Based on the 1993 US. National
Electrical Code
For Unbalanced AC TIG Welding Above 180
Amps, 255A/16V/40% Duty Cycle, Auto
Balance Based on the 1993 U.S. National
Electrical Code
Type 75°C
Type 75°C
Fuse
(Super Lag)
or Breaker
Size
Input
Type 75°C
Copper Wire in
Conduit AWG
(IEC) Sizes
Copper Ground
Wire in Conduit
AWG (IEC)
Copper Ground
Wire in Conduit
AWG (IEC)
Type 75°C
Copper Wire in
Conduit AWG
(IEC) Sizes
Ampere
Input
Rating on
Nameplate
Input
Voltage /
Frequency
Amperes
Sizes
Sizes
2
2
2
2
125
100
50
81
74
37
30
85
77
46
43
41
39
34
6 (16mm )
102
92
46
37
105
96
55
53
51
48
42
6 (16mm )
208/60
230/60
6 (16mm )
4 (25mm )
2
2
2
2
6 (16mm )
6 (16mm )
8 (10mm )
4 (25mm )
2
2
2
2
10 (6mm )
10 (6mm )
460/60
10 (6mm )
8 (10mm )
2
2
2
2
50
10 (6mm )
10 (6mm )
575/60
10 (6mm )
10 (6mm )
2
2
2
2
125
100
70
6 (16mm )
6 (16mm )
200/50/60
220/50/60
380/50/60
400/50/60
415/50/60
440/50/60
500/50/60
6 (16mm )
4 (25mm )
2
2
2
2
6 (16mm )
8 (10mm )
8 (10mm )
4 (25mm )
2
2
2
2
8 (10mm )
8 (10mm )
8 (10mm )
8 (10mm )
2
2
2
2
60
10 (6mm )
10 (6mm )
10 (6mm )
8 (10mm )
2
2
2
2
60
10 (6mm )
10 (6mm )
10 (6mm )
8 (10mm )
2
2
2
2
60
10 (6mm )
10 (6mm )
10 (6mm )
8 (10mm )
2
2
2
2
50
10 (6mm )
10 (6mm )
10 (6mm )
10 (6mm )
PHYSICAL DIMENSIONS
Height
Width
Depth
Weight
30.5 in.
19.0 in.
(Lift bail, add 3.5 in)
30.0 in.
300 lbs
(137 kg)
775 mm
485 mm
760 mm
(Lift bail, add 90 mm)
(1)
Unbalanced TIG welding above 180 amps will draw higher input currents; see Supply Connections section.
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A-2
INSTALLATION
Read entire installation section before starting
installation.
HIGH FREQUENCY INTERFERENCE
PROTECTION
SAFETY PRECAUTIONS
The spark gap oscillator in the high frequency genera-
tor, being similar to a radio transmitter, can be blamed
for many radio, TV and electronic equipment interfer-
ence problems. These problems may be the result of
radiated interference. Proper grounding methods can
reduce or eliminate radiated interference.
WARNING
ELECTRIC SHOCK can kill.
• Only qualified personnel should
perform this installation.
Radiated interference can develop in the following
four ways:
• Turn the input power OFF at the
disconnect switch or fuse box
before working on this
equipment.
1. Direct interference radiated from the welder.
• Do not touch electrically hot
parts.
2. Direct interference radiated from the welding leads.
• Always connect the Square Wave
TIG 255 grounding terminal
(located on the bottom of the
input connection box) to a good
electrical earth ground.
3. Direct interference radiated from feedback into the
power lines.
4. Interference from re-radiation of “pickup” by un-
grounded metallic objects.
Keeping these contributing factors in mind, installing
equipment per the following instructions should
minimize problems.
SELECT SUITABLE LOCATION
Place the welder where clean cooling air can freely
circulate in through the rear louvers and out through
the side louvers. Dirt, dust or any foreign material that
can be drawn into the welder should be kept at a
minimum. Failure to observe these precautions can
result in excessive operating temperatures and
nuisance shut-downs. Square Wave TIG 255 power
sources carry an IP23 enclosure rating. They are
rated for use in damp, dirty environments subject to
occasional falling water such as rain.
1. Keep the welder power supply lines as short as
possible and completely enclose them in rigid
metallic conduit or equivalent shielding for a
minimum distance of 50 feet (15.2m). There
should be good electrical contact between this
conduit and the welder. Both ends of the conduit
should be connected to a driven ground and the
entire length should be continuous.
2. Keep the work and electrode leads as short as
possible and as close together as possible.
Lengths should not exceed 25 ft (7.6m). Tape the
leads together when practical.
STACKING
Square Wave TIG 255’s cannot be stacked.
3. Be sure the torch and work cable rubber coverings
are free of cuts and cracks that allow high
frequency leakage. Cables with high natural
rubber content, such as Lincoln Stable-Arc® better
resist high frequency leakage than neoprene and
other synthetic rubber insulated cables.
TILTING
Each machine must be placed on a secure, level
surface, either directly or on a recommended
undercarriage. The machine may topple over if this
procedure is not followed.
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A-3
INSTALLATION
FIGURE A.1 — REAR PANEL
4. Keep the torch in good repair and all connections
tight to reduce high frequency leakage.
5. The work terminal must be connected to a ground
within ten feet of the welder, using one of the
following methods:
1
2
a) A metal underground water pipe in direct
contact with the earth for ten feet or more.
b) A 3/4” (19mm) galvanized pipe or a 5/8”
(16mm) solid galvanized iron, steel or copper
rod driven at least eight feet into the ground.
The ground should be securely made and the
grounding cable should be as short as possible
using cable of the same size as the work cable, or
larger. Grounding to the building frame electrical
conduit or a long pipe system can result in re-
radiation, effectively making these members
radiating antennas.
3
4
6. Keep all access panels and covers securely in
place.
1. RATING PLATE
2. INPUT ENTRY HOLE
3. RECONNECT PANEL
4. 220V RECEPTACLE & BREAKER
(50/60 HZ MACHINE ONLY)
5. 115V RECEPTACLE & BREAKER
7. All electrical conductors within 50 ft (15.2m) of the
welder should be enclosed in grounded rigid
metallic conduit or equivalent shielding. Flexible
metallic conduit is generally not suitable.
GROUND CONNECTION
8. When the welder is enclosed in a metal building,
several good earth driven electrical grounds (as in
5 (b) above) around the periphery of the building
are recommended.
The frame of the welder must be grounded. A ground
terminal marked with the symbol
the bottom of the input box for this purpose. See your
local and national electrical codes for proper
grounding methods.
is located at
Failure to observe these recommended installation
procedures can cause radio or TV interference
problems and result in unsatisfactory welding
performance resulting from lost high frequency
power.
INPUT SUPPLY CONNECTIONS
Have a qualified electrician connect single phase input
power leads to L1 and L2 of the input panel in accor-
dance with all local codes and national electrical
codes. Refer to the connection diagram located on the
inside of the cover of the Reconnect Panel.
INPUT CONNECTIONS
Be sure the voltage, phase, and frequency of the input
power is as specified on the rating plate, located on
the rear of the machine. Refer to Figure A.1.
Welder supply line entry provision is in the case rear
panel with a removable cover over the input
connection panel area. Entry is through a 1.7 in
(43mm) diameter hole in the case back. See Figure
A.1.
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A-4
INSTALLATION
FIGURE A.2. - FRONT PANEL
RECONNECT PROCEDURE
On multiple input voltage welders, be sure the recon-
nect panel is connected per the following instructions
for the voltage being supplied to the welder.
1
4
2
3
CAUTION
L
9
1
1
9
-
1
DC
I
Failure to follow these instructions can cause immedi-
ate failure of components within the welder.
POWER
AC
D
W
O
H
N
O
E
T
W
S
E
W
L
I
D
T
I
C
N
H
G
I
L
O
___________________________________________
DC
WARNING
L
9
1
1
9
-
2
G
A
S
E
L
E
C
T
R
O
D
E
W
A
T
E
R
W
O
R
K
R
E
M
O
T
E
I
N
O
U
T
I
N
O
U
T
Welders are shipped connected for the highest input
voltage as listed on the rating Plate. To change this
connection for a different input voltage, reconnect the
power strap (P) to the terminal corresponding to the
input voltage used. Designations on reconnect panel,
LOW, MID and HIGH correspond to the nameplate
input voltages of a triple voltage welder. Dual voltage
welders use only LOW and HIGH. Single voltage
welders use only HIGH.
7
8
6
5
1. CONTROL AND DISPLAY AREA 5. OPTIONAL WATER SOLENOID
EXAMPLE: On a 208/230/460 volt welder, LOW is
208V, MID is 230V, and HIGH is 460V.
2. POWER SWITCH
3. THERMOSTATIC
PROTECTION LIGHT
4. POLARITY SWITCH
6. GAS SOLENOID
7. WORK (LEFT) AND
ELECTRODE TERMINALS
8. REMOTE RECEPTACLE
Fuse the input circuit with the recommended super lag
1
fuses or delay type circuit breakers. Choose an input
and grounding wire size according to local or national
codes, refer to Specification page at the beginning of
this chapter. Using fuses or circuit breakers
smaller than recommended may result in “nuisance”
shut-offs from welder inrush currents even if not
welding at high currents.
OUTPUT CONNECTIONS
WARNING
To avoid receiving a high frequency shock, keep the
TIG torch and cables in good condition.
___________________________________________
Unbalanced AC TIG welding draws higher input
currents than those for stick, DC TIG, or Balanced AC
TIG welding. The welder is designed for these higher
input currents. However, where unbalanced AC TIG
welding above 180 amps is planned, the higher input
currents require larger input wire sizes and fuses.
Refer to Specification page at the beginning of this
chapter.
See Figure A.2 for the location of the work and
electrode terminals, the gas and optional water
solenoids, and the Remote Receptacle.
TIG TORCH CONNECTION
The Square Wave TIG 255 should be permanently
wired into the power system. Plugs or connectors
are not recommended.
TIG welding torches come with 12.5 ft (3.8m) and 25 ft
(7.6m) cables. Use the shorter length whenever
possible to minimize possible radio interference
problems. With power source off, connect the torch
cable to the “Electrode” terminal on the welder.
Connect a separate work cable to the “Work” terminal
of the welder. See Table A.1 for recommended work
cable sizes. Both work and electrode cables should be
routed through the cable strain relief holes provided in
the base directly below the welding output terminals.
1
Also called “inverse time” or “thermal/magnetic” circuit breakers; circuit
breakers which have a delay in tripping action that decreases as the magni-
tude of the current increases.
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A-5
INSTALLATION
STICK ELECTRODE CABLE CONNECTION
TABLE A.1
Cable Sizes for Combined Lengths of Copper
Electrode and Work Cable
Turn the Power switch Off. Run the electrode and
work cables through the strain relief holes below the
welding output terminals, and connect the cables to
the proper terminals. This strain relief prevents dam-
age to the welding output terminals if the cables are
pulled excessively. Select cable size according to
Table A.1.
Lengths up to
Machine Size
100 ft
100 to 200 ft
200 to 250 ft
255 Amp
40% Duty Cycle
2
2
2
#2 (35mm )
#1 (45mm )
1/0 (55mm )
Connect the TIG torch gas and water fittings to the
welder fittings. Any torch with fittings that conform to
Compressed Gas Association (CGA) standards can be
used.
WARNING
Do not connect a TIG torch and stick electrode cable
at the same time. They will both be electrically HOT
whenever the output contactor is energized.
The welder fittings have the following threads: Gas
Inlet and Outlet: 5/8”-18 right-hand female; Water inlet
and Outlet: 5/8”-18 left-hand female. The cylinder of
inert shielding gas must be equipped with a pressure
regulator and flow meter. Install a hose between the
flow meter and gas inlet on the welder.
___________________________________________
WARNING
Observe the safety precautions necessary for han-
dling and using compressed gas containers. Contact
your supplier for specific information.
___________________________________________
DO NOT operate a water-cooled torch unless water is
flowing. Water doesn’t flow until solenoid is actuated.
If using a water-cooled torch with a Magnum water
cooler, connect the cooler water outlet to the ‘Water
Valve In” fitting. Connect the TIG torch inlet to the
“Water Valve Out” fitting.
If using a water-cooled torch with a free-running water
supply, install a water line between the welder “Water
Inlet” and the supply. Include a strainer in the water
supply line to prevent dirt particles from obstructing
water flow in the valve and cooling chamber of the
TIG torch. Failure to do so could result in water valve
malfunction and overheating of the water-cooled
torch. Connect the torch water line to the welder
“Water Out” fitting. Use a nonmetallic drain line from
the electrode connection to the drain or water recircu-
lating pump.
For other water coolers or torches, consult the manu-
facturer’s instructions for the water cooler or TIG torch
being used.
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Section B
TABLE OF CONTENTS
- OPERATION SECTION -
Operation..........................................................................................................Section B
Safety Precautions.................................................................................................B-1
Graphic Symbols..........................................................................................B-2 - B-3
General Description ...............................................................................................B-4
Design Features and Advantages..........................................................................B-4
Welding Capability .................................................................................................B-5
Limitations..............................................................................................................B-5
Controls and Settings.............................................................................................B-6
Control Panel Keys .........................................................................................B-6
Case Front Controls........................................................................................B-7
Hand and Foot Amptrol Operation .........................................................................B-8
Welding Operation.......................................................................................B-8 - B-11
TIG Welding Guidelines ..................................................................................B-8
TIG Welding Sequence of Operation (2-Step Mode) ......................................B-9
TIG Welding Sequence of Operation (4-Step Mode) ....................................B-10
Advanced Tig Welding Features...................................................................B-11
Auxillary Power ....................................................................................................B-11
Overload Protection .............................................................................................B-12
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B-1
OPERATION
OPERATING INSTRUCTIONS
Read and understand entire section before operating
machine.
GENERAL WARNINGS
SAFETY PRECAUTIONS
WARNING
ELECTRIC SHOCK
can kill.
• Do not touch electrically live parts
or electrode with skin or wet
clothing.
• Insulate yourself from work and
ground.
• Always wear dry insulating
gloves.
FUMES AND GASES
can be dangerous.
• Keep your head out of fumes.
• Use ventilation or exhaust to
remove fumes from breathing
zone.
WELDING SPARKS
can cause fire or
explosion
• Keep flammable material away.
• Do not weld on containers that
have held combustibles.
ARC RAYS
can burn.
• Wear eye, ear and body
protection.
Observe additional Safety Guidelines detailed in
the beginning of this manual.
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B-2
OPERATION
GRAPHIC SYMBOLS THAT APPEAR ON
THIS MACHINE OR IN THIS MANUAL
AFTERFLOW /
AFTERFLOW
TIME
TIG 2-STEP
TIG 4-STEP
&
2
CONTINUOUS
HIGH FRE-
QUENCY
STICK
START ONLY
HIGH FRE-
QUENCY
CURRENT
CONTROL
OUTPUT
OFF
ON
LOCAL CUR-
RENT CON-
TROL
REMOTE CUR-
RENT CON-
TROL
CLEAN
(INCREASE
POSITIVE
POLARITY)
&
&
INCREASE
PENETRATE
(INCREASE
NEGATIVE
POLARITY)
OUTPUT
A
DECREASE
TIG PULSER
HIGH FRE-
QUENCY
HF
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B-3
OPERATION
GRAPHIC SYMBOLS THAT APPEAR ON
THIS MACHINE OR IN THIS MANUAL (CONT.)
AC WAVE BAL-
GAS OUTPUT
ANCE
PULSED PER
SECOND
f
GAS INPUT
OVER TEMPER-
ATURE
ELECTRODE
CONNECTION
INPUT
POWER
PROTECTIVE
GROUND
DC+
POLARITY
&
&
SINGLE PHASE
TRANSFORMER
AC & DC RECTI-
FIER POWER
SOURCE
DC-
POLARITY
DO NOT
SWITCH
WHILE WELD-
ING
TIG (GTAW)
WARNING
SINGLE
PHASE
WATER
(COOLANT)
OUTPUT
WORK CONNEC-
TION
WATER
(COOLANT)
INPUT
AC POLARITY
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B-4
OPERATION
• Welding current limit can be preset from 5 to 315
amps and is displayed on the Ammeter when not
welding.
GENERAL DESCRIPTION
The Square Wave TIG 255 is a constant current,
single range square wave AC/DC TIG (GTAW) arc
welding power source with built-in high frequency
stabilization. It also has stick (SMAW) capability. It is
available from the factory in one model only; there are
no factory installed options, only variations in input
voltage and frequency.
• Auto Balance circuitry automatically provides the
proper amount of cleaning and penetration when
AC TIG welding. Manual AC wave balance adjust-
ment is also possible.
• 2-Step/4-Step Arc Start Switch Capability.
The Square Wave TIG 255 includes advanced
features such as Auto-Balance™, 2-Step/4-Step Arc
Start Switch operation and a TIG pulser. In addition,
fixed preflow and variable afterflow timers are
included for shielding gas and cooling water control.
• TIG Pulser with On/Off Selection, and Pulses Per
Second adjustment. Background current and duty
cycle are automatically adjusted according to the
peak welding current.
• Fixed preflow time of 0.5 seconds. Preflow time is
eliminated if welding restarts during gas afterflow of
previous weld. This avoids unnecessary delays
when making repeated welds.
RECOMMENDED PROCESSES AND
EQUIPMENT
The Square Wave TIG 255 is recommended for the
TIG (GTAW) and stick (SMAW) welding processes
within its output capacity of 5 to 315 amps, on both
AC and DC polarity. It is compatible with all Magnum
TIG accessories (see Accessory section in this manu-
al), as well as many industry standard items, such as
TIG torches, hoses, and water coolers.
• Adjustable afterflow time control.
• Local/Remote current selection.
• Stick/TlG selection.
• Continuous/Start/Off High Frequency selection.
• DC+/AC/DC- Polarity Switch.
•
Power Factor Correction for lower input currents and
smaller input wire sizes.
OPERATIONAL FEATURES AND
CONTROLS
• Remote Receptacle for Amptrol or Arc Start Switch.
The Square Wave TIG 255 has the following controls
as standard: TIG 2-Step/TlG 4-Step/Stick mode selec-
tion, Local/Remote current control selection,
Continuous/Start Only/Off high frequency selection,
Auto/Manual AC wave balance selection with the
manual wave balance adjustment, TIG pulser On/Off
selection with frequency adjustment, afterflow adjust-
ment, and DC+/DC-/AC polarity selection.
• Low Voltage Arc Start Switch Circuit (24 V AC) for
maximum operator safety.
• Gas and optional Water Valves: Inlet & outlet fittings
conform to Compressed Gas Association (CGA)
standards.
• Built-in High Frequency Generator.
• 115 Volt Receptacle with 10 amp Circuit Breaker.
DESIGN FEATURES AND
ADVANTAGES
• 220 Volt European (Schuko) type receptacle with 2
amp circuit breaker for water coolers (50/60Hz
machines only).
• Designed to NEMA EW-1 & International IEC-974
Standards.
• Excellent arc starting and stability up through 315
amps.
• Single output range of 5-315 amps covers the
majority of all TIG welding applications.
• High resistance to AC arc rectification.
• Solid State Output Contactor: no noise, no parts to
wear.
• No tungsten spitting within current range of
electrode.
• Digital Ammeter and Voltmeter for precise readings
from 5 to 315 amps welding.
• Compact size, requires only a 19 in x 30 in
(485 mm x 760 mm) footprint.
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B-5
OPERATION
• Strain relief holes in base for welding cables, gas
and water hoses and control cables.
• Easy access for input connections. Connections
are simple strip and clamp of input wires (no lugs
required).
• Low fan noise at idle.
• Modular construction for easy servicing.
• Simple keypad layout allows even novice users to
operate with minimal instruction.
• Unused controls are automatically locked out to
simplify setup. Examples: the AC wave balance
control has no effect in DC; the High Frequency and
gas and water valves do not operate in Stick mode;
TIG Pulser is locked out in the Stick mode.
• Recessed panels protect controls, output terminals
gas and water fittings.
• Large safety margins and protective circuits protect
rectifiers from transient voltages and high currents.
• Line Voltage Compensated.
• Thermostatically Protected.
• Electronic Over Current Protection.
WELDING CAPABILITY
The Square Wave TIG 255 is rated at 255 amps, 30
volts, at 40% duty cycle on a ten minute basis. It is
capable of higher duty cycles at lower output currents.
If the duty cycle(s) are exceeded, a thermal protector
will shut off the output until the machine cools to a
reasonable operating temperature.
LIMITATIONS
The Square Wave TIG 255 is not recommended for
arc gouging due to its limited output capacity.
The Square Wave TIG 255 is not recommended for
AC TIG welding when high concentrations of helium
are used for shielding; starting problems and arc recti-
fication may occur.
The Square Wave TIG 255 is not recommended for
pipe thawing.
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B-6
OPERATION
CONTROLS AND SETTINGS
All operator controls and adjustments are located on the case front of the Square Wave TIG 255. Refer to Figures
B.1, B.2.a and B.2.b and corresponding explanations.
FIGURE B.1 - CONTROL PANEL KEYS
7
G2612
AC/DC OUTPUT CAPACITY: 255 AMPS 30 VOLTS 40% DUTY CYCLE
THE LINCOLN ELECTRIC COMPANY CLEVELAND, OHIO USA
AC WAVE BALANCE
CURRENT CONTROL
TIG PULSER
WELD MODE
HF HIGH FREQUENCY
2
AFTERFLOW
LOCAL
REMOTE
TIG 2-STEP
CONTINUOUS
SECONDS
OFF
ON
HF
AUTO-
BALANCE
MANUAL
BALANCE
AMPS
TIG 4-STEP
START ONLY
HF
PULSES PER SECOND
CLEAN
2
f
STICK
A
PENETRATE
OFF
LINCOLN
ELECTRIC
R
6
2
4
1
5
3
1. WELD MODE KEYS
5. TIG PULSER KEYS
6. AFTERFLOW KEYS
7. DISPLAY
2. CURRENT CONTROL KEYS
3. HIGH FREQUENCY KEYS
4. AC WAVE BALANCE KEYS
4. AC WAVE BALANCE: These keys are active in
the AC TIG mode only. They are used to set the
amount of cleaning and/or penetration produced
during an AC TIG weld. Auto Balance™
automatically sets the AC Wave Balance according
to the welding current. If manual adjustment is
desired, the Manual Balance key can be pressed,
and the balance adjusted from +5 (cleaning) to -10
(penetration) with the Cleaning and Penetration
keys. Read the Advanced Features section for a
complete explanation of the AC Wave Balance.
CONTROL PANEL KEYS
The keys are grouped into six areas, described below
and in Figure B.1. Some areas are active in both TIG
and Stick, while others are active in TIG only. The red
LED indicator lights are used to tell which functions
are active, and the display (Item 1) is used to check
the settings of the up/down keys.
1. WELD MODE KEYS: These keys select the Weld
Mode desired: TIG 2-Step, TIG 4-Step, or Stick.
Read the complete Operating Instructions section
for more information on TIG 2-Step and TIG 4-
Step.
5. TIG PULSER: These keys are active in the TIG
mode only. The On/Off keys turn the TIG Pulser
on and off. The Pulses Per Second keys adjust
the pulsing frequency up and down, from 0.5 to 10
pulses per second. Read the Advanced Features
section for more information on the TIG Pulser.
2. CURRENT CONTROL: These keys select Local
or Remote and adjust the Amps Up or Amps
Down. These keys are used to set thewelding cur-
rent from 5 to 315 amps, as well as to select Local
or Remote control. Local control allows the current
to be adjusted only with the Amps Up/Amps Down
keys. Remote control allows the use of a hand or
foot operated remote control. Read the complete
Operating Instructions section for more information
on Local and Remote.
6. AFTERFLOW: These keys are active in the TIG
mode only. They must adjust the afterflow time
from 5 to 50 seconds for shielding gas and cooling
water flow through solenoids located on the case
front. As the Afterflow time is adjusted, the
Afterflow time, in seconds, is shown in the
Momentary Display.
3. HIGH FREQUENCY: These keys are active in the
TIG mode only. Select from Continuous, Start
Only, or Off. Read the TIG Welding Section for
information on High Frequency.
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B-7
OPERATION
7. CONTROL PANEL: The display is divided into five
sections. See Figures B.2.a and B.2.b.
and on the Momentary Display. When the Momentary
Display is blank (as in Figure B.2.a), the Bar Graph
Display represents values shown on the ammeter.
When a low value is shown on the ammeter, only a
few “bars” will appear on the left hand side of the Bar
Graph Display. As the ammeter value increases, more
and more “bars” will appear. Whenever a value
increases, more and more “bars” will appear.
Whenever a value appears in the Momentary Display,
the Bar Graph Display will represent the Momentary
Display value, not the ammeter value.
FIGURE B.2.a - DISPLAY
C
D
A
B
CASE FRONT CONTROLS
E
Refer to Figure B.3 for the location of the following
controls:
A. AC/DC INDICATOR
B. VOLTMETER
C. AMMETER
D. MOMENTARY DISPLAY
E. BAR GRAPH
1. POWER SWITCH: Controls the input power to the
Square Wave TIG 255.
FIGURE B.2.b - DISPLAY
2. OVER TEMPERATURE LIGHT: A yellow light
which only lights when an over temperature
situation occurs. See the Maintenance Section for
more information on the thermostatic protection.
3. POLARITY SWITCH: Selects DC+, AC or DC-
welding polarity. DO NOT SWITCH UNDER
LOAD.
A. AC/DC INDICATOR: This symbol represents the
output polarity of the 255 . . . either AC or DC. AC
is shown in Figure B.2.a; DC is shown in Figure
B.2.b.
FIGURE B.3 - CASE FRONT CONTROLS
B. VOLTMETER: This meter displays open circuit
voltage as well as welding voltage, as measured
on the output studs of the Square Wave TIG 255.
3
1
2
C. AMMETER: The ammeter can display preset
current (for setting the welding current before
welding) and actual welding current (the value of
the welding current during a weld).
L
9
1
1
9-1
DC
I
POWER
AC
DO NOT SWITCH
WHILE WELDING
O
DC
WARNING
D. MOMENTARY DISPLAY: This area is blank under
most conditions; see Figure B.2.a. Different val-
ues may be displayed here as certain keypad
keys are pressed. See Figure B.2.b; the TIG
Pulser is being adjusted, so the Pulse Frequency,
2.0 Hz, is being displayed. Information in the
Momentary Display lasts for five seconds after a
key is pressed. Read the complete Operating
Instructions section for more information on the
values that appear in the Momentary Display.
L
9
1
1
9-2
GAS
ELECTRODE
WATER
WORK
REMOTE
IN
OUT
IN
OUT
1.
2.
POWER SWITCH
THERMOSTATIC
PROTECTION LIGHT
POLARITY SWITCH
E. BAR GRAPH DISPLAY: This area provides a
graphical display of values shown on the Ammeter
3.
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B-8
OPERATION
WELDING OPERATION
HAND AND FOOT AMPTROL
ACCESSORY OPERATION
TIG WELDING
Both the Hand and Foot Amptrol work in a similar
manner. They are meant to be used for remote current
control when Remote Current Control is selected.
The TIG 2-Step mode must be selected when using
an Amptrol for remote current control. As explained
below, Amptrols can also be used as arc start
switches if Local Current Control is selected.
Familiarize yourself with the Controls and Display
Section before attempting operation of the Square
Wave TIG 255.
TIG WELDING GUIDELINES
TIG welding can be done in either the TIG 2-Step or
the TIG 4-Step Weld Mode. TIG 2-Step is typically
used with Hand or Foot Amptrols, with Remote
Current control. TIG 4-Step is typically used with Arc
Start switches and Local Current Control, because it
provides a very brief current upslope, and a 5-second
current downslope. TIG 4-Step also functions like a
trigger interlock, making it unnecessary to hold down
the Arc Start switch during a weld. Read the TIG
Welding Sequence of Operation sections for more
details on 2-Step and 4-Step Operation.
For simplicity, the following explanation will refer only
to “Amptrols”, meaning both Foot and Hand models.
The term “minimum” refers to a Foot pedal in the “up”
position, as it would be with no foot pressure, or a
Hand Amptrol in the relaxed position, with no thumb
pressure. “Maximum” refers to a fully depressed Foot
Amptrol, or a fully extended Hand Amptrol.
The Amptrol is capable of controlling the output
current from 5 amps to the preset current displayed on
the ammeter. For example, if the ammeter is preset
for 200 amps and the Current Control switch is in the
REMOTE position, the Amptrol, when depressed just
past its minimum position, will cause the Square
Wave TIG 255 to weld at 5 amps. At the Amptrols
maximum position, the output would be near 200
amps.
Refer to Table B.2 for guidelines on electrode sizes,
torch nozzles and shielding gas flow rates.
TABLE B.1
RECOMMENDED POLARITY SETTINGS FOR
TIG WELDING
Electrode
Polarity
High Frequency
Setting
Type of Welding
It is important to note that, for many applications, the
tungsten will not start an arc at only 5 amps. To start
an arc reliably, it is important to depress the Amptrol
far enough so that the machine output current is near
the tungsten operating range. In the example above, a
3/32” tungsten may be used on DC- to weld near 200
amps. To start the weld, the operator may have to
depress the Amptrol approximately 1/4 of the way
down, or to nearly 50 amps, in order to start the arc.
Merely depressing the Amptrol to its 5 amp minimum
position will not start the arc.
Stainless Steel
DC-
AC
START
CONTINUOUS
START
Aluminum & Magnesium
Other Metals
DC-
If the Current Control switch is set to the LOCAL
position, an Amptrol can be used as an arc start
switch. Depressing the Amptrol just past minimum will
cause the Amptrols built-in arc start switch to close,
and backing off completely causes the built-in start
switch to open. The Amptrol will have no effect on the
welding current when used as an arc start switch.
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B-9
OPERATION
TABLE B.2
TYPICAL CURRENT RANGES (1) FOR TUNGSTEN ELECTRODES (2)
AC
Approximate Argon
Gas Flow Rate
C.F.H. (1/min.)
+
-
DCEN (
)
DCEP (
)
Unbalanced Wave
Balanced Wave
1%, 2%
1%, 2%
Tungsten
1%, 2%
Thoriated
Tungsten
1%, 2%
Thoriated
Tungsten
Thoriated
Tungsten
Zirconiated
Thoriated
Tungsten
Zirconiated
Electrode
Diameter
in. (mm)
TIG Torch
Nozzle
Pure
Tungsten
Pure
Tungsten
Stainless
Steel
Size(4), (5)
Aluminum
(3)
(3)
(3)
.010 (.25)
0.020 (.50)
0.040 (1.0)
2-15
5-20
15-80
2-15
5-15
10-60
2-15
5-20
15-80
2-15
10-20
20-30
---
5-20
20-60
3-8
(2-4) 3-8
(2-4) #4, #5, #6
5-10 (3-5) 5-10 (3-5)
5-10 (3-5) 5-10 (3-5)
1/16 (1.6)
3/32 (2.4)
70-150
10-20
50-100
70-150
30-80
60-120
5-10 (3-5) 9-13 (4-6)
#5, #6
150-250
250-400
15-30
25-40
100-160
150-210
140-235
225-325
60-130
100-180
100-180
160-250
13-17 (6-8) 11-15 (5-7) #6, #7, #8
15-23 (7-11)
1/8
(3.2)
11-15 (5-7)
5/32 (4.0)
3/16 (4.8)
400-500
500-750
40-55
55-80
80-125
200-275
250-350
325-450
300-400
400-500
500-630
100-240
190-300
250-400
200-320
290-390
340-525
13-17 (6-8)
18-22 (8-10)
23-27(11-13)
#8, #10
21-25 (10-12)
23-27 (11-13)
28-32 (13-15)
1/4
(6.4) 750-1000
(1)
(2)
When used with argon gas. The current ranges shown must be reduced when using argon/helium or pure helium shielding gasses.
Tungsten electrodes are classified as follows by the American Welding Society (AWS):
Pure . . . . . . . . . . . . . . . EWP
1% Thoriated . . . . . . . . EWTh-1
2% Thoriated . . . . . . . . EWTh-2
Though not yet recognized by the AWS, Ceriated Tungsten is now widely accepted as a substitute for 2% Thoriated Tungsten in AC and DC applications.
DCEP is not commonly used in these sizes.
TIG torch nozzle “sizes” are in multiples of 1/16ths of an inch:
(3)
(4)
#4 = 1/4 in.
#5 = 5/16 in.
#6 = 3/8 in.
#7 = 7/16 in.
#8 = 1/2 in.
#10 = 5/8 in.
(6 mm)
(8 mm)
(10 mm)
(11 mm)
(12.5 mm)
(16 mm)
(5)
TIG torch nozzles are typically made from alumina ceramic. Special applications may require lava nozzles, which are less prone to breakage, but cannot with-
stand high temperatures and high duty cycles.
5. Select Continuous High Frequency if welding with
TIG WELDING SEQUENCE OF
OPERATION (2-STEP MODE)
AC polarity, or Start Only High Frequency if
welding with DC- polarity. High Frequency Off can
be used for scratch start welding.
In TIG 2-Step Mode the welding arc is established by
depressing the Arc Start Switch or Amptrol (Step 1).
Output continues as long as the switch or Amptrol is
depressed. Releasing the switch or Amptrol (Step 2)
turns off the arc. Hence the name 2-Step Mode.
6. Select AC or DC- electrode polarity. See Table
B.1.
7. If welding with AC polarity, select Auto Balance™.
This gives the optimum ratio between cleaning and
penetration, automatically adjusted for the output
current. If manual adjustment of the AC Wave
Balance is desired, select Manual Balance, and
adjust the wave balance with the Cleaning and
Penetration keys. See the Advanced Features
section for more information on setting and using
the AC Wave Balance.
1. Connect an Arc Start Switch or an Amptrol to the
Remote Receptacle.
2. Turn on the welder, gas supply and water supply (if
so equipped). The Control Panel Display and
red LEDS will illuminate when the power is on.
3. Select the TIG 2-Step Weld Mode.
8. Select TIG Pulser On or Off. If the TIG Pulser is
on, adjust the pulse frequency with the Pulses
Per Second Up/Down keys. See the Advanced
Features section for more information on setting
and using the TIG Pulser.
4. Select Local (if using an Arc Start Switch) or
Remote (if using an Amptrol) current control. Set
the output current using the Amps Up/Down keys.
The output current setting will be displayed on the
Ammeter.
12/95
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B-10
OPERATION
5. Select Continuous High Frequency if welding with
AC polarity, or Start Only High Frequency if
welding with DC- polarity. High Frequency Off can
be used for scratch start welding.
9. Set the Afterflow time with the Seconds Up/Down
keys. Afterflow time provides shielding gas flow
(and cooling water, if used) after the weld. Use
short Afterflow times with low currents and small
tungstens, use long afterflow times at high output
currents with large tungstens.
6. Select AC or DC- electrode polarity. See Table
B.1.
10. Press and release the Arc Start Switch, and set
the gas flow meter. The welder is now ready for
welding.
7. If welding with AC polarity, select Auto Balance™.
This gives the optimum ratio between cleaning and
penetration, automatically adjusted for the output
current. If manual adjustment of the AC Wave
Balance is desired, select Manual Balance, and
adjust the wave balance with the Cleaning and
Penetration keys. See the Advanced Features
section for more information on setting and using
the AC Wave Balance.
11. Position the tungsten electrode at the start of the
weld at a 65° to 75° angle with the horizontal so
that the electrode is approximately 1/8” (4mm)
above the work piece. Press the Arc Start Switch.
This opens the gas and water valves to automati-
cally purge air from the hose and torch. After a 0.5
second preflow time, the high frequency becomes
available to strike the arc.
8. Select TIG Pulser On or Off. If the TIG Pulser is
on, adjust the pulse frequency with the Pulses Per
Second Up/Down keys. See the Advanced
Features section for more information on setting
and using the TIG Pulser.
12. Hold the Arc Start Switch or Amptrol down until an
arc is established. If using an Amptrol, read the
section on Hand and Foot Amptrol Operation.
Release the Arc Start Switch or Amptrol to stop
the arc and start the Afterflow timer. After the
Afterflow time has expired, the gas and water
valves will close. To make another weld, repeat
steps 11 and 12.
9. Set the Afterflow time with the Seconds Up/Down
keys. Afterflow time provides shielding gas flow
(and cooling water, if used) after the weld. Use
short Afterflow times with low currents and small
tungstens, long afterflow times at high output
currents with large tungstens.
10. Press and release the Arc Start Switch, and set
the gas flow meter. The welder is now ready for
welding.
TIG WELDING SEQUENCE OF
OPERATION (4-STEP MODE)
TIG 4-Step Mode funcitons like a trigger interlock,
making it unnecessary to hold down the Arc Start
Switch during welding. By depressing the Arc Start
Switch a first time, the arc will start at a low current
(step 1). By releasing the Arc Start Switch (step 2) the
output ramps up to welding current. Depressing the
Arc Start Siwtch a second time (step 3) initiates a
welding current downslope. Releasing the Arc Start
Switch (step 4) stops the arc. Hence the name “4-Step
Mode”
11. Position the tungsten electrode at the start of the
weld at a 65° to 75° angle with the horizontal so
that the electrode is approximately 1/8” (4mm)
above the work piece. Press the Arc Start Switch.
This opens the gas and water valves to
automatically purge air from the hose and torch.
After a 0.5 second preflow time, the high
frequency becomes available to strike the arc.
12. Hold the Arc Start Switch down until an arc is
established. The arc will start at a low current
value. Release the Arc Start Switch. At this point,
the Square Wave TIG 255 will quickly ramp up to
the welding current, and the weld will continue
indefinitely. Press the Arc Start Switch a second
time to initiate a 5-second downslope. The current
will go down to a crater fill current that is equal to
25% of the welding current. Release the Arc Start
Switch to stop the arc and start the Afterflow timer.
After the Afterflow time has expired, the gas and
water valves will close. To make another weld,
repeat steps 11 and 12.
1. Connect an Arc Start Switch to the Remote
Receptacle.
2. Turn the welder, gas supply and water supply (if so
equipped), on. The Control Panel Display and red
lights will illuminate when the power is on.
3. Select the TIG 4-Step Weld Mode.
4. Select the Local current control. Set the output
current using the Amps Up/Down keys. The output
current setting will be displayed on the Ammeter.
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B-11
OPERATION
Up/Down. Adjustment of the pulses per second (pulse
frequency), allows for control of the heat input into the
work piece. This adjustment can reduce distortion and
burnthrough on thin guage base metal. When the
Pulser is turned On, or when the Pulses Per Second
are adjusted, the pulse frequency is shown in the
Momentary Display. It can be varied from 0.5 Hz to 10
Hz in 0.5 Hz increments. (One Hertz {Hz} is equivalent
to one pulse per second.) The background current
(the welding current at the low point of the pulse
cycle) is automatically adjusted from 40% to 60% of
the peak current by the Square Wave TIG 255. The
duty cycle (the ratio between that time spent at the
peak current vs, the time spent at the background cur-
rent) is fixed at 50%.
ADVANCED TIG WELDING FEATURES
AC WAVE BALANCE AND AUTO BALANCE™
AC Wave Balance is a feature unique to square wave
TIG power sources. It is active only in AC TIG mode.
It controls the amount of positive and negative current
in the AC output.
The Square Wave TIG 255 allows the operator to
select Auto Balance™. This selection provides
automatic adjustment of the AC Wave Balance; it is
suitable for most welding conditions. Auto Balance
gives the ideal amount of cleaning and penetration,
based on the welding current output.
Manual adjustment of the AC Wave Balance is also
possible. Select the Manual Balance key, and the
Balance setting will appear in the Momentary Display.
Manual Balance settings vary from +5 (maximum
cleaning) to -10 (maximum penetration). A setting of
0 yields a balanced output (equal amounts of cleaning
and penetration). Use the following as a guide when
setting the Balance manually:
AUXILIARY POWER
ALL MACHINES
The Square Wave TIG 255 provides 10 amps of 115
volt AC power at a standard NEMA 5-15R receptacle,
located on the lower case back of the machine. This
circuit is protected from shorts and overloading by a
10 amp circuit breaker, located next to the receptacle.
The auxiliary circuit is intended for running water cool-
ers and small power tools, whose current draw is with-
in the 10 amp rating.
BALANCED (0): The amounts of positive and
negative are the same.
CLEANING (+1 to +5): Provides more positive
current than negative. Since the positive
current produces the “cleaning” or oxide
removal on aluminum, this setting is used for
welding on heavily oxidized aluminum.
CAUTION
PENETRATION (-1 to -10): Provides more negative
current than positive. The arc plasma will be
more concentrated and more easily directed
to where the heat is needed. Higher
penetration settings allow a given size of
tungsten to carry more current.
Note that some types of equipment, especially pumps
and large motors, have starting currents which are sig-
nificantly higher than their running current. These
higher starting currents may cause the circuit breaker
to open. If this situation occurs, the user should refrain
from using the Square Wave TIG 255 auxiliary for that
equipment.
CAUTION: Use only the amount of cleaning required
because the greater amount of positive current will
heat the tungsten more and possibly cause it to melt
or “spit”. Also, the arc is usually more flared and less
stable with more cleaning current.
___________________________________________
50/60Hz MACHINES
In general, use just enough “cleaning” to remove
oxides and to give good wetting to the puddle.
Square Wave TIG 255 machines rated for 50/60Hz
operation provide 2 amps of 220 volt AC power at a
continental European (Schuko) type receptacle, locat-
ed on the lower case back of the machine. This circuit
is protected from shorts and overloading by a 2 amp
circuit breaker, located above the receptacle. The aux-
iliary circuit is intended for running water coolers
whose current draw is within the 2 amp rating of the
receptacle.
TIG PULSER
The Square Wave TIG 255 contains a unique TIG
Pulser circuit. The TIG Pulser has On/Off selections,
as well as adjustments for Pulses Per Second
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B-12
OPERATION
CAUTION
Note that some types of equipment, especially pumps
and motors, have starting currents which are signifi-
cantly higher than their running currents. These higher
starting currents may cause the circuit breaker to
open. If this situation occurs, the user should refrain
from using the Square Wave TIG 255 auxiliary for that
equipment.
___________________________________________
OVERLOAD PROTECTION
This welder has thermostatic protection from
excessive duty cycles, overloads, loss of cooling, and
high ambient temperatures. When the welder is
subjected to an overload or loss of cooling, a
thermostat will open. This condition will be indicated
by the illumination of the yellow Thermostatic
Protection Light on the case front (see Figure A.2).
Also, the Display will be blank, and all of the red
Control Panel lights will be out. The fan will continue
to run to cool the power source. No welding is
possible until the machine is allowed to cool and the
Thermostatic Protection Light goes out.
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B-13
NOTES
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Section C
TABLE OF CONTENTS
- ACCESSORIES SECTION -
Accessories......................................................................................................Section C
Available Option and Accessories .........................................................................C-1
Undercarriage Function .........................................................................................C-1
Installation of Field Installed Options .....................................................................C-1
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C-1
ACCESSORIES
OPTIONS / ACCESSORIES
• Hand Amptrol (K812)
• Foot Amptrol (K870)
• Arc Start Switch (K814)
• Magnum Cooler Horizontal TIG Mounting Bracket
(K559-2)
• Undercarriage (K932-1)
UNDERCARRIAGE FUNCTION
The Square Wave TIG 255 is designed to be used
with a Lincoln K932-1 Undercarriage. Complete
installation instructions are included with the K932-1
undercarriage. When the undercarriage is properly
installed, the Square Wave TIG 255 lift bail is non-
functional. Do not attempt to lift the power source with
the undercarriage attached. The undercarriage is
designed for hand moving only; mechanized towing
can lead to injury and/or damage to the Square Wave
TIG 255.
INSTALLATION OF FIELD
INSTALLED OPTIONS
Instructions for connecting the K932-1 Undercarriage
and the K559-2 Magnum Cooler Horizontal TIG
Mounting Bracket are included with those acces-
sories.
Installation of the K812 Hand Amptrol, the K814 Arc
Start Switch and K870 Foot Amptrol are as follows:
Lift the Output Cover Door (if so equipped) on the
Square Wave TIG 255. Feed the cable up through the
strain relief holes in the base, and connect the 6-pin
MS-type (Amphenol) connector to the Remote
Receptacle (See Figure A.2). Secure with the thread-
ed collar.
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Section D
TABLE OF CONTENTS
- MAINTENANCE SECTION -
Maintenance .....................................................................................................Section D
Safety Precautions.................................................................................................D-1
Routine and Periodic Maintenance........................................................................D-1
General Assembly Exploded View.........................................................................D-2
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D-1
MAINTENANCE
MAINTENANCE
SAFETY PRECAUTIONS
WARNING
ELECTRIC SHOCK can kill.
• Only qualified personnel should
perform this maintenance.
• Turn the input power OFF at the
disconnect switch or fuse box
before working on this
equipment.
• Do not touch electrically hot
parts.
ROUTINE AND PERIODIC
MAINTENANCE
WARNING
To avoid receiving a high frequency shock, keep the
TIG torch and cables in good condition.
1. Disconnect power supply lines to machine before
performing periodic maintenance.
2. Periodically clean the inside of the machine with a
low pressure air system. Be sure to clean the fol-
lowing components thoroughly. See Figure D.1
for location of those components.
• Main Transformer
• Output Terminals
• Polarity Switch
• Rectifier Assembly
• Control Box Assembly
• Spark Gap Assembly
• Protection PC Board -
(Mounted to rear of control box assembly)
3. Inspect welder output and control cables for
fraying, cuts, and bare spots.
4. Keep TIG torch and cables in good condition.
5. The fan motor has sealed ball bearings which
require no maintenance.
6. Inspect spark gap spacing at regular intervals to
maintain a 0.015 in (0.4mm) gap. (Smallest
possible air gap consistent with good welding is
desirable to minimize R.F.I. problems.) Dressing
or any refinishing of the spark gap contacts is not
recommended. If the contact surfaces become
irregular or completely eroded, replacement of both
electrodes is recommended.
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D-2
MAINTENANCE
FIGURE D.1 - GENERAL ASSEMBLY EXPLODED VIEW
4
7
5
1
6
2
3
1, MAIN TRANSFORMER
2. OUTPUT TERMINALS
3. POLARITY SWITCH
4. RECTIFIER ASSEMBLY
5. CONTROL BOX ASSEMBLY
6. SPARK GAP ASSEMBLY
7. PROTECTION PC BOARD -
(Mounted to rear of control box assembly)
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D-3
NOTES
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Section E
TABLE OF CONTENTS
- THEORY OF OPERATION SECTION -
Theory of Operation Section...........................................................................Section E
Power Supply Operation ...............................................................................E-1 - E-5
Input Line Voltage and Main Transformer.......................................................E-1
Output Rectification and Feedback Control ....................................................E-2
High Voltage / High Frequency Circuit............................................................E-3
DC Welding Output .........................................................................................E-4
AC Welding Output .........................................................................................E-5
SCR Operation.......................................................................................................E-6
Thermal Protection.................................................................................................E-7
POWER SUPPLY BLOCK LOGIC DIAGRAM
BY-PASS
POLARITY
BOARD
SWITCH
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LINE
SWITCH
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
DC+
SCR
BRIDGE
AC
X2
SHUNT
X1
AC
DC-
CHOKE
POWER
FACTOR
CAPACITORS
ARC START
115 VAC
LCD DISPLAY
PROTECTION
SNUBBER
BOARD
KEYPAD
LED
BOARD
115VAC
CONTROL
BOARD
FAN
GATE SIGNALS
HI-FREQ
115 VAC
KEYPAD
24 VAC
18 VAC
16 VAC
CONTROL
TRANSFORMER
115 VAC
RECEPTACLE
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
HIGH FREQUENCY SPARK
REMOTE
RECEPTACLE
NOTE: On subsequent pages areas of this diagram that are the topic of discusstion are shown in white, other
portions of the circuit are shaded.
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E-1
THEORY OF OPERATION
INPUT LINE VOLTAGE AND MAIN TRANSFORMER
BY-PASS
POLARITY
BOARD
SWITCH
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LINE
SWITCH
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
DC+
SCR
BRIDGE
AC
X2
SHUNT
X1
AC
DC-
CHOKE
POWER
FACTOR
CAPACITORS
ARC START
115 VAC
LCD DISPLAY
PROTECTION
SNUBBER
BOARD
KEYPAD
LED
BOARD
115VAC
CONTROL
BOARD
FAN
GATE SIGNALS
HI-FREQ
115 VAC
KEYPAD
24 VAC
18 VAC
16 VAC
CONTROL
TRANSFORMER
115 VAC
RECEPTACLE
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
HIGH FREQUENCY SPARK
REMOTE
RECEPTACLE
115vac auxiliary winding, that supplies 115vac to
operate the cooling fan and offers 10 Amps of auxil-
iary power at the 115vac receptacle. This 115vac is
also applied to the control board and the control trans-
former via the protection/snubber board. The 115vac
also powers the high voltage circuit. The secondary
voltages that are developed in the control transformer
power the control board. On 50/60 Hz machines
the main transformer also has a 220vac auxiliary
winding that provides power to the 220vac receptacle.
This 220vac winding is not isolated from the 115vac
winding.
The desired single-phase input power is connected to
the TIG 255 through a line switch located on the front
panel.
A reconnect panel allows the user to configure the
machine for the desired input voltage. This AC input
voltage is applied to the primary of the main trans-
former. Power factor correction capacitors are incor-
porated in the primary circuit of the main transformer
to help balance the inductive nature of the TIG 255.
The transformer changes the high voltage, low current
input power to a low voltage, high current output. In
addition, the main transformer also has an isolated
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E-2
THEORY OF OPERATION
OUTPUT RECTIFICATION AND FEEDBACK CONTROL
BY-PASS
POLARITY
BOARD
SWITCH
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LINE
SWITCH
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
DC+
SCR
BRIDGE
AC
X2
SHUNT
X1
AC
DC-
CHOKE
POWER
FACTOR
CAPACITORS
ARC START
115 VAC
LCD DISPLAY
PROTECTION
SNUBBER
BOARD
KEYPAD
LED
BOARD
115VAC
CONTROL
BOARD
FAN
GATE SIGNALS
HI-FREQ
115 VAC
KEYPAD
24 VAC
18 VAC
16 VAC
CONTROL
TRANSFORMER
115 VAC
RECEPTACLE
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
HIGH FREQUENCY SPARK
REMOTE
RECEPTACLE
The AC output from the main transformer secondary
is rectified and controlled through the SCR bridge.
Output current is sensed at the shunt, as a low volt-
age signal, and fed back to the control board. The
control board compares the commands of the keypad
(or remote control) with the shunt feedback signal.
The appropriate gate firing pulses are generated by
the control board and applied to the SCR bridge
through the protection / snubber board. The control
board controls the firing of the SCRs, thus controlling
the output of the machine. See SCR Operation. The
control board also powers and commands the keypad
LED board and the display board.
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E-3
THEORY OF OPERATION
HIGH VOLTAGE / HIGH FREQUENCY CIRCUIT
BY-PASS
POLARITY
BOARD
SWITCH
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LINE
SWITCH
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
DC+
SCR
BRIDGE
AC
X2
SHUNT
X1
AC
DC-
CHOKE
POWER
FACTOR
CAPACITORS
ARC START
115 VAC
LCD DISPLAY
PROTECTION
SNUBBER
BOARD
KEYPAD
LED
BOARD
115VAC
CONTROL
BOARD
FAN
GATE SIGNALS
HI-FREQ
115 VAC
KEYPAD
24 VAC
18 VAC
16 VAC
CONTROL
TRANSFORMER
115 VAC
RECEPTACLE
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
HIGH FREQUENCY SPARK
REMOTE
RECEPTACLE
The control board passes the 115vac through the pro-
tection / snubber board to the primary of the high volt-
age transformer. The secondary of the high voltage
transformer is coupled to a spark gap generator and
also to the high frequency transformer. The high fre-
quency transformer transfers the high frequency
“spark” to the electrode stud.
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E-4
THEORY OF OPERATION
DC WELDING OUTPUT
BY-PASS
BOARD
POLARITY SWITCH
(DC POSITION)
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LINE
SWITCH
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
DC+
SCR
BRIDGE
AC
X2
SHUNT
X1
AC
DC-
CHOKE
POWER
FACTOR
CAPACITORS
ARC START
115 VAC
LCD DISPLAY
PROTECTION
SNUBBER
BOARD
KEYPAD
LED
BOARD
115VAC
CONTROL
BOARD
FAN
GATE SIGNALS
HI-FREQ
115 VAC
KEYPAD
24 VAC
18 VAC
16 VAC
CONTROL
TRANSFORMER
115 VAC
RECEPTACLE
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
HIGH FREQUENCY SPARK
REMOTE
RECEPTACLE
When the polarity switch is placed in either DC posi-
tion, the AC voltage from the main transformer sec-
ondary is applied to the SCR bridge. The SCR bridge
and choke circuits are connected in a conventional full
wave bridge and filter configuration, resulting in a con-
trolled DC output. Since the choke is in series with
the negative leg of the bridge and also in series with
the welding load, a filtered DC is applied to the
machine’s output studs.
CHOKE
ELECTRODE
G
G
DC
PRIMARY
1Ø
G
G
WORK
DC WELDING CIRCUIT
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E-5
THEORY OF OPERATION
AC WELDING OUTPUT
BY-PASS
BOARD
POLARITY SWITCH
(AC POSITION)
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LINE
SWITCH
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
DC+
SCR
BRIDGE
AC
X2
SHUNT
X1
AC
DC-
CHOKE
POWER
FACTOR
CAPACITORS
ARC START
115 VAC
LCD DISPLAY
PROTECTION
SNUBBER
BOARD
KEYPAD
LED
BOARD
115VAC
CONTROL
BOARD
FAN
GATE SIGNALS
HI-FREQ
115 VAC
KEYPAD
24 VAC
18 VAC
16 VAC
CONTROL
TRANSFORMER
115 VAC
RECEPTACLE
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
HIGH FREQUENCY SPARK
REMOTE
RECEPTACLE
By rotating the polarity switch to the AC position the
welding power circuit is changed. One lead (X2) of
the main transformer secondary is connected to the
machine’s output work stud. The other secondary
lead (X1) is connected to one of the AC connections
on the SCR bridge. The electrode stud is connected
to the other AC side of the bridge. The choke is now
electrically across the negative and positive SCR
bridge connections. Due to the ability of the choke to
store energy and the SCR’s ability to turn on at the
appropriate times, an AC Square Wave is developed
and applied to the output studs.
CHOKE
G
G
ELECTRODE
G
G
AC
PRIMARY
1Ø
WORK
AC WELDING CIRCUIT
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E-6
THEORY OF OPERATION
SCR OPERATION
A silicon controlled rectifier (SCR) is a three terminal
device used to control rather large currents to a load.
An SCR acts very much like a switch. When a gate
signal is applied to the SCR it is turned ON and there
is current flow from anode to cathode. In the ON state
the SCR acts like a closed switch. When the SCR is
turned OFF there is no current flow from anode to
cathode thus the device acts like an open switch. As
the name suggests, the SCR is a rectifier, so it passes
current only during positive half cycles of the AC sup-
ply. The positive half cycle is the portion of the sine
wave in which the anode of the SCR is more positive
than the cathode.
An SCR is fired by a short burst of current into the
gate. This gate pulse must be more positive than the
cathode voltage. Since there is a standard PN junc-
tion between gate and cathode, the voltage between
these terminals must be slightly greater than 0.6V.
Once the SCR has fired it is not necessary to continue
the flow of gate current. As long as current continues
to flow from anode to cathode the SCR will remain on.
When the anode to cathode current drops below a
minimum value, called holding current, the SCR will
shut off. This normally occurs as the AC supply volt-
age passes through zero into the negative portion of
the sine wave. If the SCR is turned on early in the
positive half cycle, the conduction time is longer
resulting in greater SCR output. If the gate firing
occurs later in the cycle the conduction time is less
resulting in lower SCR output.
When an AC supply voltage is applied to the SCR, the
device spends a certain portion of the AC cycle time in
the on state and the remainder of the time in the off
state. The amount of time spent in the ON state is
controlled by the Gate.
INPUT
CATHODE
OUTPUT
NOTE: AS THE GATE
PULSE IS APPLIED
LATER IN THE CYCLE
THE SCR OUTPUT
IS DECREASED.
ANODE
GATE
GATE
SCR OPERATION
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E-7
THEORY OF OPERATION
THERMAL PROTECTION
A thermostat protects the machine from excessive
operating temperatures. Excessive operating temper-
atures may be caused by a lack of cooling air or oper-
ating the machine beyond the duty cycle and output
rating. If excessive operating temperature should
occur, the thermostat will prevent output voltage or
current and the yellow indicator light will glow.
Additionally, the display and keypad lights will turn off.
The fan will remain on during this period. The thermo-
stat is self-resetting once the machine cools sufficient-
ly. If the thermostat shutdown is caused by excessive
output or duty cycle and the fan is operating normally,
the power switch may be left on and the reset should
occur within a 15 minute period. If the fan is not turn-
ing or the air intake louvers are obstructed, then the
input power must be removed and the fan problem or
air obstruction be corrected.
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Section F
TABLE OF CONTENTS
- TROUBLESHOOTING & REPAIR SECTION -
Troubleshooting & Repair Section................................................................Section F
Safety Precautions.................................................................................................F-1
How to Use Troubleshooting Guide.......................................................................F-1
PC Board Troubleshooting Procedures .................................................................F-2
Troubleshooting Guide................................................................................F-3 - F-15
PC Board Connector Locations ...........................................................................F-16
Test Procedures
Control Transformer Voltage Test .................................................................F-17
Protection/Snubber Board Continuity Test ....................................................F-20
Arc Start Trigger Circuit Test .........................................................................F-23
Static SCR Test .............................................................................................F-26
Active SCR Test ............................................................................................F-28
Oscilloscope Waveforms
Normal Open Circuit Voltage Waveform DC Stick Mode...............................F-31
Normal Open Circuit Voltage Waveform AC Stick Mode...............................F-32
Normal Open Circuit Voltage Waveform DC TIG Mode ................................F-33
Normal Open Circuit Voltage Waveform AC TIG Mode.................................F-34
Typical Output Voltage Waveform Machine Loaded DC TIG Mode ..............F-35
Typical Output Voltage Waveforms Machine Loaded AC TIG Mode.............F-36
Typical SCR Gate Voltage Waveform ...........................................................F-37
Abnormal Open Circuit Voltage Waveform DC Stick Mode...........................F-38
Abnormal Open Circuit Voltage Waveform AC Stick Mode...........................F-39
Replacement Procedures
Fan Motor and Blade Removal......................................................................F-40
SCR Heatsink Assembly Removal ................................................................F-42
Retest After Repair ..............................................................................................F-44
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F-1
TROUBLESHOOTING & REPAIR
HOW TO USE TROUBLESHOOTING GUIDE
WARNING
Service and Repair should only be performed by Lincoln Electric Factory Trained Personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician and
machine operator and will invalidate your factory warranty. For your safety and to avoid
Electrical Shock, please observe all safety notes and precautions detailed throughout this
manual.
__________________________________________________________________________
This Troubleshooting Guide is provided to
help you locate and repair possible machine
malfunctions. Simply follow the three-step
procedure listed below.
Step 3. PERFORM COMPONENT TESTS.
The last column labeled “Recommended
Course of Action” lists the most likely com-
ponents that may have failed in your
machine. It also specifies the appropriate
test procedure to verify that the subject
component is either good or bad. If there
are a number of possible components,
check the components in the order listed to
eliminate one possibility at a time until you
locate the cause of your problem.
Step 1. LOCATE PROBLEM (SYMPTOM).
Look under the column labeled “PROBLEM
(SYMPTOMS)”. This column describes
possible symptoms that the machine may
exhibit. Find the listing that best describes
the symptom that the machine is exhibiting.
Symptoms are grouped into three main cat-
egories: output problems, function prob-
lems, welding problems.
All of the referenced test procedures refered
to in the Troubleshooting Guide are
described in detail at the end of this chap-
ter. Refer to the Troubleshooting and Repair
Table of Contents to locate each specific
Test Procedure. All of the specified test
points, components, terminal strips, etc. can
be found on the referenced electrical wiring
diagrams and schematics. Refer to the
Electrical Diagrams Section Table of
Contents to locate the appropriate diagram.
Step 2. PERFORM EXTERNAL TESTS.
The second column labeled “POSSIBLE
AREAS OF MISADJUSTMENT(S)” lists the
obvious external possibilities that may con-
tribute to the machine symptom. Perform
these tests/checks in the order listed. In
general, these tests can be conducted with-
out removing the case wrap-around cover.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric Service Department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be sup-
ported. Failure to do this could result in mechanical or electrical damage to the
TIG 255. This is best accomplished with a wooden block. Refer to Figure F.3 as
an example.
_____________________________________________________________________
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
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F-2
TROUBLESHOOTING & REPAIR
PC BOARD TROUBLESHOOTING PROCEDURES
4. Test the machine to determine if the fail-
ure symptom has been corrected by the
replacement PC board.
WARNING
ELECTRIC SHOCK can
kill.
Have an electrician install and
service this equipment. Turn the
input power OFF at the fuse box
before working on equipment. Do
not touch electrically hot parts.
NOTE: Allow the machine to heat up so
that all electrical components can reach
their operating temperature.
5. Remove the replacement PC board and
substitute it with the original PC board to
recreate the original problem.
CAUTION: Sometimes machine failures
appear to be due to PC board failures.
These problems can sometimes be traced
to poor electrical connections. To avoid
problems when troubleshooting and replac-
ing PC boards, please use the following
procedure:
a. If the original problem does not reap-
pear by substituting the original board,
then the PC board was not the prob-
lem. Continue to look for bad connec-
tions in the control wiring harness,
junction blocks, and terminal strips.
1. Determine to the best of your technical
ability that the PC board is the most like-
ly component causing the failure symp-
tom.
b. If the original problem is recreated by
the substitution of the original board,
then the PC board was the problem.
Reinstall the replacement PC board
and test the machine.
2. Check for loose connections at the PC
board to assure that the PC board is
properly connected.
6. Always indicate that this procedure was
followed when warranty reports are to be
submitted.
3. If the problem persists, replace the sus-
pect PC board using standard practices
to avoid static electrical damage and
electrical shock. (Read the warning
inside the static resistant bag.)
NOTE: Following this procedure and writ-
ing on the warranty report, “INSTALLED
AND SWITCHED PC BOARDS TO VERIFY
PROBLEM,” will help avoid denial of legiti-
mate PC board warranty claims.
NOTE: It is desirable to have a spare
(known good) PC board available for PC
board troubleshooting.
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F-3
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
OUTPUT PROBLEMS
Major Physical or Electrical
Damage is Evident.
1. Contact The Lincoln Electric
Service Dept. (216) 383-2531
or 1-800-833-9353 (WELD).
1. Check input power switch (S1).
It may be faulty.
Machine is Dead -
No Output - No Fan
No Displays.
1. Make certain that the input
power switch is in the “ON”
position.
2. Check for open or broken pri-
mary leads to main transformer
(T1).
2. Check the input voltage at the
machine. Input voltage must
match the rating plate and
reconnect the panel.
3. Check auxiliary (115vac) power
winding in the main transformer
(T1).
3. Blown or missing fuses in
input line.
1. Secondary thermostat may be
open. Check for glowing yel-
low light on front panel
Fan runs - Display and control
panel dark. No output from
machine in either Stick or TIG
modes.
1. Check for proper input
voltages. As per nameplate
and reconnect panel.
2. Control transformer (T2) may
be faulty. See Control
Transformer Voltage Test.
3. Protection/Snubber board may
be faulty. See
Protection/Snubber Board
Continuity Test.
4. Control Board may be faulty.
Replace.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
12/95
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F-4
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENT(S)
RECOMMENDED
COURSE OF ACTION
OUTPUT PROBLEMS
1. Check for loose connectors at
the SCR bridge and at the
The voltmeter reads “00” in Stick
Mode, and there is no output from
the machine when in the TIG
2-Step Mode.
1. Inspect to assure that the arc
start switch is in the on
Protection/Snubber board. (J10)
and (J11). See Figure F.2 at
end of this Guide for location.
(closed) position when
welding in the TIG Mode.
2. Check the wiring to the Control
Transformer (T2). Observe
directions on decal.
3. The Protection/Snubber board
may be faulty. See
Protection/Snubber Board
Continuity Test.
4. Check the Control Transformer
(T2). See Control Transformer
Voltage Test.
5. Check the polarity switch (S2)
for loose or broken connections.
6. Check the SCR bridge. See
Static and Active SCR Tests.
7. If all previous tests are OK -
then replace the Control board.
1. Check trigger circuit. See Arc
Start Trigger Circuit Test
Machine does not respond (no gas 1. Machine MUST be in one of
flow, no high frequency and no
open circuit voltage) when arc
switch or amptrol is activated -
displays and fan working. Note:
Machine may have OCV in the
Stick Mode.
the TIG Modes.
2. Check the Control transformer
(T2). See Control Transformer
Voltage Test.
2. The arc start switch or amptrol
may be defective. Check for
continuity between pins “D”
and “E” on cable connector
when arc switch or amptrol is
activated.
3. Protection/Snubber board may
be faulty. See
Protection/Snubber Board
Continuity Test.
4. If all previous tests are OK -
then replace the Control board.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-5
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
OUTPUT PROBLEMS
1. If voltage at the receptacle is
zero, then check for open cir-
cuit breaker (CB1)
115VAC Receptacle not working
properly (voltage is below 108VAC).
Machine has welding output - fan is
running.
1. Check for 115VAC at
receptacle - if low (below
108VAC), then check input
voltage to machine.
2. Check leads #230, #231, and
#232 for loose or broken con-
nections. Refer to wiring dia-
gram.
Machine regularly overheats - ther- 1. Welding application may
1. Check for proper fan operation.
mostat opens, PL1 (yellow light on
front panel) glows. The fan runs
but machine has no output and no
display.
exceed recommended duty
cycle.
2. The thermostat may be faulty -
Should be normally closed
2. Dirt and dust may have
clogged the cooling channels
inside the machine. Blow out
unit with clean, dry
compressed air.
3. Air intake and exhaust louvers
may be blocked due to
inadequate clearance around
machine.
Machine makes a very loud
buzzing noise in DC Stick Mode, or
in DC TIG Mode when the arc start
or amptrol is pressed.
1. Inspect output stud insulators
for cracks or signs of over-
heating.
1. Diode (D1) may be shorted.
Check and replace if neces-
sary.
2. The SCR bridge may be faulty.
See Static and Active SCR
Tests.
There is no current draw from
machine’s output studs.
(The machine is not externally
loaded).
3. Check the polarity switch (S2)
for correct connections.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-6
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENT(S)
RECOMMENDED
COURSE OF ACTION
OUTPUT PROBLEMS
None.
The ammeter displays a very high
value (greater than 316 amps)
when the machine is not loaded.
Machine may have low or no out-
put.
1. The shunt leads (#221 and
#222) may be loose or open.
Check the red and white twist-
ed pair from the shunt to the
control board. Refer to wiring
diagram.
2. The Control board may be
faulty. If the shunt leads have
continuity (zero ohms) to the
control board, pins 1J7 and
2J7, then replace the control
board. See pin locations in
Figure F.1 at end of this Guide.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-7
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
FUNCTION PROBLEMS
The yellow light (PL1) on the front
panel is not lit.
1. Normal condition - this light
will glow only if machine is in
an overheated condition.
(Thermal overload).
1. Check the Keypad LED board
to the Control board harness.
The plugs may be loose or
defective.
One or more keypad lights (LEDS)
are dark and cannot be lit when
their respective keys are pressed -
machine is operable.
1. Be sure that the proper weld
mode is selected. For
example, the high frequency
keys and keypad lights
(LEDS) are not active in the
stick mode.
2. If only one red LED won’t light,
the LED PC Board may be
defective. Replace.
3. If three or more red LEDS do
not light, the Control board may
be faulty. Replace.
1. Watch the Control Panel
Display to see if the keys are
responding properly to key
presses. If so then the Buzzer
may be defective. Replace the
Piezo Electric Buzzer. HINT-
The Piezo Electric Buzzer
may be checked by applying
a 9vdc signal to the buzzer
leads. Red lead to +. Black
lead to –.
The Beeper (Piezoelectric Buzzer)
cannot be heard - machine operat-
ing normally.
1. Background noise may be too
loud for user to hear beeper.
2. The Control board may be
faulty. Check for the presence
of 15vdc at pins 6J6 to 13J6 at
the Control board. See figure
at end of this Guide. The 15vdc
will be present for a very short
period of time when a key is
pressed. If the voltage is not
present then replace the
Control board.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-8
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENT(S)
RECOMMENDED
COURSE OF ACTION
FUNCTION PROBLEMS
None
The control panel displays cannot
be read. The characters run, dis-
play only half characters, or ran-
dom dots may appear on display.
1. Check for loose connections at
plug J3 on the control board.
2. The display may be faulty.
Replace.
3. The control board may be
faulty. Replace.
None
The voltmeter always reads “00” .
The machine output is normal.
1. Check the continuity of leads
#305 and #313C and their con-
nections to the machine output
studs. Refer to wiring diagram.
2. The Control board may be
faulty. Check for machine
“open citcuit voltage” at 5J6
and 12J6 on the Control board.
If open circuit voltage is pre-
sent then replace the Control
board.
3. If open circuit voltage is not
present at 5J6 and 12J6 (see
Figure F.1) then check the
Protection/Snubber board. See
Protection/Snubber Board
Continuity Test.
None
The control panel display back-
ground is dark instead of red. The
machine operates normally.
1. Check for loose connector (P3)
at the Control board.
2. The Control board may be
faulty. Disconnect P3 from the
Control board. Check voltage
from 1J3 to 2J3 on the board.
See Figure F.1. The voltage
should be 15 to 20vdc. If the
voltage is not correct then
replace the Control board.
3. If the Control board is good
then the Display may be faulty.
Replace Display.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-9
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
FUNCTION PROBLEMS
AC/DC Indicator on control panel
display show AC when polarity
switch is in the DC position, or vice
versa — machine has output but
balance control is not operable in
the AC TIG mode.
None
1. Check leads #304 and #312 for
proper connections. Refer to
wiring diagram
2. Check microswitch (S2A),
located on polarity switch (S2),
for proper operation.
3. The protection/snubber board
may be faulty. See protection/
snubber board continuity test.
4. Check control transformer (T2).
See control transformer voltage
test.
5. If above checks are OK, then
replace the control board.
All red keypad LEDS are dark
but the control panel display is
operable. The machine has output.
None
1. The wiring harness between
the Control board and the LED
board may be faulty. Check for
defective plugs or loose wires.
2. The Control board may be
faulty. Replace.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-10
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENT(S)
RECOMMENDED
COURSE OF ACTION
TIG MODE PROBLEMS
1. Internal ground connections
may be loose. Check mounting
Machine output is intermittently
lost. Gas flow and high frequency
are also interrupted.
1. Problem may be caused by
high frequency interference.
Make sure that the machine is
grounded properly according
to the installation instructions.
If there are other high
screws on the Protection/
Snubber board and also on the
Bypass board. All case screws
should be in place and tight.
frequency sources in the area,
make certain that they are
grounded properly.
2. Protection/Snubber board may
be faulty. See Protection/
Snubber Board Continuity Test.
2. Check arc start switch or
amptrol for proper operation
and loose connections.
3. Check trigger circuit. See Arc
Start Trigger Circuit Test.
1. Check for loose shunt connec-
tions.- leads #221 and #222.
Refer to wiring diagram.
Arc “Flutters” when TIG welding.
1. Tungsten electrode may be
too large in diameter.
2. Tungsten not “Sharp” when
welding in DC negative mode.
2. Check polarity switch for loose
or faulty connections.
3. If helium is used as a
shielding gas, then reduce the
percentage of helium.
3. SCR bridge may be faulty. See
Static and Active SCR Tests.
4. Protection/Snubber board may
be faulty. See Protection/
4. Adjust flow rate of shielding
gas.
Snubber Board Continuity Test.
5. Check hoses and connections
for leaks.
5. Check R3, R4 and C2 in the
high voltage transformer prima-
ry circuit. Refer to wiring dia-
gram.
6. The Control board may be
faulty.-Replace.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-11
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
TIG MODE PROBLEMS
1. SCR bridge may be faulty. See
Static and Active SCR Tests.
Lack of penetration in AC TIG
welding.
1. Manual balance control set
improperly - set to negative
10 (-10) for maximum
penetration.
2. Protection/Snubber board may
be faulty. See Protection/
Snubber Board Continuity Test.
3. Control board may be faulty.-
Replace.
Black areas along weld bead.
1. Tungsten electrode may be
contaminated. Replace or
sharpen.
This may be a welding procedure
problem.
Contact The Lincoln Electric
Service Department (216) 383-
2531 or 1-800-833-9353 (WELD).
2. Shielding gas flow may be
insufficient.
3. Contaminated gas or faulty
gas line or torch.
Black areas along weld bead at or
near end of weld.
1. Increase post flow time.
This may be a welding procedure
problem.
Contact The Lincoln Electric
Service Department (216) 383-
2531 or 1-800-833-9353 (WELD).
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-12
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENT(S)
RECOMMENDED
COURSE OF ACTION
TIG MODE PROBLEMS
Machine has low output when in
TIG 4-Step Mode.
1. Machine must be in “Local”
Control Mode when 4-Step is
used.
Machine controls may be set incor-
rectly.
Contact The Lincoln Electric
Service Department (216) 383-
2531 or 1-800-833-9353 (WELD).
Weak high frequency - machine
has normal welding output.
1. Spark gap may be misadjusted.
Check and reset per
1. Check for an open or arcing
high frequency component.
Replace as required.
maintenance instructions.
(Examples. R3, R4, C2.) Refer
to wiring diagram.
2. Improper shielding gas flow.
Adjust for a flow of 10 to 30
CFH (4.7 to 14.1 l/min.) for
most applications.
2. If spark is weak at the spark
gap check or replace high fre-
quency circuit. ( Examples. T3,
C3, L3, L4.)
3. Work and electrode cables in
poor condition allowing high
frequency to “Leak Off”. Use
good quality cables with a high
natural rubber content, such
as Lincoln Stable Arc Cable.
Cables should be as short as
possible.
The display shows zero amps, but
indicates open circuit voltage
(approximately 53V). The arc start
switch or amptrol is not actuated.
1. The arc start switch or amptrol
may be defective. There should
not be any continuity between
pins “D” and “E” on the arc start
cable connector, unless the
unit is actuated.
1. Check Trigger circuit. See Arc
Start Trigger Circuit Test.
2. Control board may be faulty.
Replace.
2. If an amptrol is not being used,
the machine must be in the
Local Control Mode.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-13
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
TIG WELDING PROBLEMS
High frequency “Spark” is present
at tungsten electrode, but operator
1. Torch may be faulty.
This may be a welding procedure
problem.
is unable to establish a welding arc. 2. If an amptrol is not being used,
Machine has normal open circuit
voltage (approximately 53V).
then the machine must be in
the Local Control Mode.
Contact The Lincoln Electric
Service Department (216) 383-
2531 or 1-800-833-9353 (WELD).
3. Tungsten electrode may be
too large for the process.
4. If helium shielding gas is being
used, then reduce percentage
of helium.
5. If TIG welding in the DC
negative mode, then a properly
sharpened thoriated tungsten
should be used.
6. Check the welding cables and
output stud connections.
No high frequency. Machine is
in the TIG Mode and has normal
output.
1. In order for the high frequency
to operate, the machine must
be either in the start only
Mode or the continuous high
frequency mode.
1. Check the high voltage trans-
former (T3). The normal resis-
tance of the secondary winding
of the high voltage transformer
is 12.5k ohms. 115vac is
applied to the primary of T3. A
very high voltage is developed
on the secondary winding. For
assistance call The Lincoln
Electric Service Department.
(216) 383-2531 or 1-800-833-
9353 (WELD).
2. The high frequency spark gap
may be too large or shorted.
Check gap as per
maintenance instructions.
2. Check the values of R3, R4
and C2. Replace if faulty.
3. The Protection/Snubber board
may be faulty. See
Protection/Snubber Board
Continuity Test.
4. The Control board may be
faulty. Replace.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-14
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENT(S)
RECOMMENDED
COURSE OF ACTION
TIG WELDING PROBLEMS
No gas or water flow when arc start 1. Gas supply is empty or not
Possible gas or water supply
problem.
switch or amptrol is activated in the
TIG Mode. Machine has output -
fan runs. When toggling between
the Stick and TIG Modes a “Click”
can be heard indicating that the
solenoids are operating.
turned on.
2. Gas or water hose may be
pinched.
Contact The Lincoln Electric
Service Department (216) 383-
2531 or 1-800-833-9353(WELD).
3. Gas or water solenoid may be
blocked with dirt. Use filters
to prevent reoccurrence.
Consult your Local welder/gas
distributor.
Arc rectification when AC TIG weld- 1. Tungsten electrode may be
1. Check components R3, R4,
and C2 in the high voltage
transformer primary circuit.
Replace if faulty.
ing.
too small for process.
2. Manual balance control may
be misadjusted. Readjust to
the negative direction.
2. Check the SCR bridge. See
Static and Active SCR Tests.
3. If helium gas is being used,
reduce percentage of helium.
There is no gas or water flow when None
the arc start switch or amptrol is
activated in the TIG mode. The
machine has output and the fan
runs. When toggling between the
Stick and TIG modes a “click”
1. The gas or water solenoid may
be defective.
Check for 115vac at the sole-
noid leads. The machine must
be in the TIG mode and the arc
start switch activated.
CANNOT be heard indicating that
the solenoids are NOT operating.
2. If 115vac is not present at the
solenoids then check the
Protection/Snubber board. See
Protection/Snubber Board
Continuity Test.
3. If the above tests are OK -
Then the Control board may be
faulty. Replace.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-15
TROUBLESHOOTING & REPAIR
Observe Safety Guidelines
detailed in the beginning of this manual.
TROUBLESHOOTING GUIDE
PROBLEMS
POSSIBLE AREAS OF
RECOMMENDED
(SYMPTOMS)
MISADJUSTMENT(S)
COURSE OF ACTION
STICK WELDING PROBLEMS
Stick electrode “Blasts Off” when
arc is struck.
1. Weld current is set too high
for recommended electrode
size. Reduce preset current
adjustment.
1. Possible faulty SCR bridge.
See Static and Active SCR
Tests.
2. Control board may be faulty.
Replace.
Cannot adjust AC Wave Balance
when welding in the Stick Mode.
1. This is a normal condition.
Wave balance keys are
automatically disabled in the
Stick Mode.
None
Machine welds at a very low output 1. If welding in the Remote
1. Check the SCR bridge. See
Static and Active SCR Tests.
regardless of the preset current set-
ting - arc is stable.
Control Mode, the remote
amptrol may be defective or
not installed properly.
2. Check polarity switch (S2)
connections and operation.
2. If the output is low when the
machine is in the Local
Control Mode, the problem
could be internal to the
machine.
3. Check the control transformer
(T2). See Control Transformer
Voltage Test.
4. The Control board may be
faulty. Replace.
Variable or sluggish welding arc
when welding in the Stick Mode.
1. Check work and electrode
cables for loose or poor
connections.
1. Check polarity switch (S2) for
wear or loose connentions.
2. Check interior connections of
the heavy current carrying
leads.
2. The weld cables may be too
small or too long to permit the
desired current to flow.
3. The preset current adjustment
may be set too low.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353.
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F-16
TROUBLESHOOTING & REPAIR
PC BOARD CONNECTOR LOCATIONS
1J3
12J6
13J6
2J3
J7
J1
J2
J3
J6
J4
J8
J5
6J6
5J6
G2150
SQUARE WAVE 255 CONTROL
FIGURE F.1 - CONTROL BOARD CONNECTORS
1J13
1J14
1J11
1J15
J15
1J12
1J10
PROTECTION/SNUBBER
L9255
J10
J13
J14
J11
J12
12J10
10J11
14J12
16J13
8J14
6J15
FIGURE F.2 - PROTECTION/SNUBBER BOARD CONNECTORS
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F-17
TROUBLESHOOTING & REPAIR
CONTROL TRANSFORMER (T2) VOLTAGE TEST
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
This test will determine if the correct voltage is being applied to the primary of the con-
trol transformer and also if the correct voltages are being induced on the secondary
windings of the transformer.
MATERIALS NEEDED
Volt/Ohmmeter (Multimeter)
TIG 255 Wiring Diagrams (See Electrical Diagram Section of manual.)
Table of Voltage Tests and Drawing of Transformer and Molex Plug (J8)
Figure F.4.
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F-18
TROUBLESHOOTING & REPAIR
CONTROL TRANSFORMER (T2) VOLTAGE TEST (continued)
SUPORT CASE BACK
AND CENTER BAFFLE
WITH WOOD 2 X 4
CONTROL BOX
CONTROL BOARD LOCATED INSIDE
CONTROL TRANSFORMER LOCATED INSIDE
FIGURE F.3 - LOCATION OF CONTROL BOARD AND CONTROL TRANSFORMER.
5. Check for 120VAC at leads #432 to
#433
TEST PROCEDURE
1. Remove main supply power to machine
A.. If 120VAC is present at leads #432
to #433, go to Step 8.
2. Locate and remove Plug J8 from control
board, located in the control box. Hint:
For ease of testing, secure Plug J8 to
case front with tape.
Note: If main supply voltage varies,
control transformer voltages will
vary accordingly.
3. Locate leads #432 and #433 connected
to the control transformer (T2) which is
located in the top of the control box.
B. If a very low or zero voltage is
shown at leads #432 to #433 then
go to Step 6.
4. Turn main power ON
6. Remove main supply power to machine.
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F-19
TROUBLESHOOTING & REPAIR
CONTROL TRANSFORMER (T2) VOLTAGE TEST (continued)
7
8
1
RED (1)
(7)
WHITE
(2)
2
RED
(3)
(9)
BLACK
BLACK
3
9
YELLOW (10)
(4)
YELLOW
4
10
11
12
(11)
BLUE
BLUE (5)
5
6
(12)
(6)
ORANGE
ORANGE
PLUG P8
G2150
SQUARE WAVE 255 CONTROL
FIGURE F.4 - CONTROL BOARD AND TRANSFORMER.
7. Test the resistance from 8J14, on the
protection/ snubber board, to the #432
lead at the control transformer. Also
check resistance from 4J14, on the pro-
tection/snubber board, to the #433 lead
at the control transformer.
IMPORTANT: If the Control Transfor-
mer is replaced refer to label on the
new transformer for correct primary lead
connections. If connected wrong, the
machine will have no OCV output. If no
OCV occurs reverse the control trans-
former’s primary connections and re-
check machine’s OCV.
A. If zero ohms resistance is shown
test is OK. Proceed to protection/
snubber board continuity test.
Note: If main supply voltage varies, con-
trol transformer voltages will vary
accordingly.
B. If resistance of any value is shown,
check wires and connections.
Secondary
Lead Colors
Approximate
Voltages
8. Test for the correct AC voltages at Plug
8. See Figure F-4.
Plug P8
Red to Red
Red to White
1 to 2
1 to 7
36 VAC
18 VAC
16 VAC
24 VAC
16 VAC
16 VAC
A. If one or more voltages are missing
or incorrect, control transformer is
faulty. Replace.
Yellow to Yellow
Black to Black
Orange to Orange
Blue to Blue
4 to 10
3 to 9
6 to 12
5 to 11
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F-20
TROUBLESHOOTING & REPAIR
PROTECTION/SNUBBER BOARD CONTINUITY TEST
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
Many circuits pass through the protection/snubber board. The purpose of this test is to
determine if the board’s circuitry and components are intact and capable of passing
signal currents.
MATERIALS NEEDED
Ohmmeter (Multimeter)
TIG 255 Wiring Diagrams (see Electrical Diagram section of manual)
Protection/snubber board Continuity Table, Figure F.6.
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F-21
TROUBLESHOOTING & REPAIR
PROTECTION/SNUBBER BOARD CONTINUITY TEST (continued)
SUPORT CASE BACK
AND CENTER BAFFLE
WITH WOOD 2 X 4
CONTROL BOX
PROTECTION/SNUBBER BOARD
LOCATED ON BACK OF CONTROL BOX
FIGURE F.5 - PROTECTION/SNUBBER BOARD LOCATION
4. Inspect board for “leaky” or burned
components. If questionable compo-
nents are observed then replace projec-
tion/snubber board. (See note.)
TEST PROCEDURE
1. Remove main supply power to machine.
2. Locate and remove all harness plugs
from the protection/snubber board locat-
ed on the back of the control box. Refer
to Figure F.5.
5. Check resistances per Continuity Table
F.6.
A. If any resistances do not meet the
Continuity Table specifications, pro-
jection/snubber board is faulty -
Replace. (See note.)
3. The protection/snubber board may be
removed to simplify test.
A. Remove three 8 - 32 x 1/4” Phillips
head screws from bottom of board
Note: When installing projection/
snubber board be sure that the three
8 - 32 x 1/4” Phillips head mounting
screws are tightened securely. These
conduction points are necessary for
high frequency by-pass grounding.
B. Release board from nylon supports
with needle nose pliers or small
screw driver
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F-22
TROUBLESHOOTING & REPAIR
PROTECTION/SNUBBER BOARD CONTINUITY TEST (continued)
1J13
1J14
1J11
1J15
1J12
1J10
PROTECTION/SNUBBER
L9255
J10
J13
J14
J15
J11
J12
12J10
10J11
14J12
16J13
8J14
6J15
FIGURE F.6 - PROTECTION/SNUBBER BOARD TEST POINTS.
Check Points
5J13 to 5J12
13J13 to 12J12
4J13 to 4J12
12J13 to 11J12
2J13 to 2J12
9J13 to 8J12
1J13 to 1J12
11J13 to 10J12
3J13 to 3J12
5J15 to 4J14
4J15 to 8J14
4J15 to 5J14
4J15 to 3J14
6J15 to 4J14
2J15 to 2J14
3J15 to 6J14
1J15 to 1J14
1J10 to 1J11
2J10 to 2J11
7J10 to 6J11
10J10 to 9J11
9J10 to 8J11
3J10 to 3J11
4J10 to 4J11
Component(s) Being Checked
L1 and Board Trace
L2 and Board Trace
L3 and Board Trace
L4 and Board Trace
L5 and Board Trace
L6 and Board Trace
L7 and Board Trace
L8 and Board Trace
L9 and Board Trace
L10 and Board Trace
L11 and Board Trace
L12 and Board Trace
L13 and Board Trace
L10 and Board Trace
L14 and Board Trace
L15 and Board Trace
L16 and Board Trace
Board Trace
Maximum Allowable Resistance
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
4.2 OHMS (3.3 Typical)
.35 OHMS (.32 Typical)
.35 OHMS (.32 Typical)
4.2 OHMS (3.3 Typical)
.35 OHMS (.32 Typical)
.35 OHMS (.32 Typical)
.35 OHMS (.32 Typical)
.0 OHMS
Board Trace
.0 OHMS
Board Trace
.0 OHMS
Board Trace
.0 OHMS
Board Trace
.0 OHMS
Board Trace
.0 OHMS
Board Trace
.0 OHMS
TABLE F.6
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F-23
TROUBLESHOOTING & REPAIR
ARC START TRIGGER CIRCUIT TEST
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
The Arc Start Trigger Test determines if the wiring and connections are good from the
six pin amphenol receptacle to the protection/snubber board and also from the protec-
tion/snubber board to the control board.
MATERIALS NEEDED
Ohmmeter (Multimeter)
TIG 255 Wiring Diagrams (see Electrical Diagrams section of this manual)
Arc Start Trigger Circuit, (Figure F.10)
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F-24
TROUBLESHOOTING & REPAIR
ARC START TRIGGER CIRCUIT TEST (continued)
SUPORT CASE BACK
AND CENTER BAFFLE
WITH WOOD 2 X 4
CONTROL BOX
CONTROL BOARD LOCATED INSIDE
PROTECTION/SNUBBER BOARD
LOCATED ON BACK OF CONTROL BOX
FIGURE F.7 - LOCATION OF PROTECTION/SNUBBER BOARD.
Note: If arc start switch is opened or
jumper removed from pins “D” and “E”
the measured resistance in Step 4
should be infinite.
TEST PROCEDURE
1. Remove main supply power to machine
2. Remove plug J6 from the control board
5
Test the resistance between 10J6 plug
and 10J12 on the projection/snubber
board. Also check resistance from 3J6
plug to 3J12 on the projection/ snubber
board.
3. Close the arc start switch or jumper pins
“D” and “E” at the six pin amphenol
receptacle.
4. Check for continuity between pins 10J6
and 3J6 at plug J6 on the wiring har-
ness. Refer to Figure F.8. If 8.4 ohms to
6.0 ohms resistance is indicated then
arc start trigger circuit is okay. If a high
resistance or open is read then proceed
to Step 5.
A. If zero ohms resistance is indicated,
test is okay. Go to Step 6.
B. If a resistance of any value is
shown, check wires and connec-
tions.
10J6
3J6
PLUG J6 REMOVED
J2
J3
J4
J5
J7
J6
J1
J8
G2150
SQUARE WAVE 255 CONTROL
FIGURE F.8 - CONTROL BOARD TEST POINTS.
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F-25
TROUBLESHOOTING & REPAIR
ARC START TRIGGER CIRCUIT TEST (continued)
3J13
3J12
PROTECTION/SNUBBER
L9255
J15
J14
J10
J12
J13
11J13
J11
10J12
FIGURE F.9 - PROTECTION/SNUBBER BOARD TEST POINTS.
6. Test the resistance from 11J13 on the
projection/ snubber board to pin “D” on
the six pin amphenol receptacle. (Lead
#311). Also check resistance from 3J13
on the projection/snubber board to pin
“E” on the six pin amphenol receptacle.
(Lead #303).
A. If zero ohms resistance is shown
test is okay. Proceed to projection/
snubber board test.
B. If resistance of any value is shown,
check wires and connections.
FIGURE F.10 - ARC START TRIGGER CIRCUIT.
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F-26
TROUBLESHOOTING & REPAIR
STATIC SCR TEST
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
The Static SCR Test is a quick check to determine if an SCR is shorted or “leaky”. See
machine waveform section or normal and abnormal SCR waveforms.
MATERIALS NEEDED
Analog ohmmeter (Multimeter)
TIG 255 Wiring Diagrams (see Electrical Diagrams section of this manual)
SCR Heat Sink Assembly Drawing, Figure F.12
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F-27
TROUBLESHOOTING & REPAIR
STATIC SCR TEST (continued)
REMOVE PLUGS J10 & J13
PROTECTION/SNUBBER
L9255
J14
J10
J12
J13
J15
J11
FIGURE F.11 - PROTECTION BOARD PLUG LOCATIONS
SCR1. Reverse the meter leads and
check from cathode to anode of SCR1.
TEST PROCEDURE
1. Remove main supply power to machine
A. If a low resistance is indicated in
either direction SCR1 is faulty.
Replace SCR assembly.
2. Remove plug J10 and J13 from the pro-
tection/snubber board. Refer to Figure
F.11.
5. Repeat Step 4 testing SCR2, SCR3 and
SCR4.
3. Remove red insulating paint from heat
sink test points. See Figure F.12. DO
NOT DISASSEMBLE THE HEAT
SINKS.
To further check the SCR’s functions
use an SCR tester and proceed to
active SCR test.
4. Using an analog ohmmeter test the
resistance from anode to cathode of
SCR3
CATHODE
SCR2
ANODE
SCR4
CATHODE
ANODE
(3 & 4)
CATHODE
SCR1
(1 & 2)
ANODE
PLUG
P10
FIGURE F.12 - SCR TEST POINTS.
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F-28
TROUBLESHOOTING & REPAIR
ACTIVE SCR TEST
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
The Active SCR Test will determine if the device is able to be gated “ON” and conduct
current from anode to cathode.
MATERIALS NEEDED
An SCR tester as outlined in this procedure
TIG 255 Wiring Diagrams (see Electrical Diagrams section of this manual)
SCR Heat Sink Assembly Drawing, Figure F.14
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F-29
TROUBLESHOOTING & REPAIR
ACTIVE SCR TEST (continued)
REMOVE PLUGS J10 & J13
PROTECTION/SNUBBER
L9255
J14
J10
J12
J13
J15
J11
FIGURE F.13 - PROTECTION/SNUBBER BOARD PLUG LOCATIONS.
4. Perform test procedure as outlined in
Figure F.15. Repeat test for all four
SCR’s
TEST PROCEDURE
1. Remove main supply power to machine
5. Replace any SCR assembly that does
not pass test in Step 4
2. Remove plugs J10 and J13 from protec-
tion/snubber board. See Figure F.13.
3. Remove red insulating paint from heat
sink test points. See Figure F.14. DO
NOT DISASSEMBLE THE HEAT
SINKS.
SCR3
CATHODE
SCR2
ANODE
SCR4
CATHODE
ANODE
(3 & 4)
CATHODE
SCR1
(1 & 2)
ANODE
PLUG
P10
FIGURE F.14 - SCR TEST POINTS.
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F-30
TROUBLESHOOTING & REPAIR
ACTIVE SCR TEST (continued)
SW1
R2
V
R1
SW2
6volt
Lantern
Battery
A
G
SCR
C
under
test
R1= 4 ohms /10 watts
R2= 3 ohms/ 10 watts
To test SCRs construct the circuit outlined above.
Resistor values are plus or minus ten percent. The
voltmeter scale should be low, approximately 0-5 or
0-10 volts DC.
FIGURE F.15 - SILICON CONTROLLED RECTIFIER TEST SETUP.
SILICON CONTROLLED
BATTERY TEST
RECTIFIER TEST
Check the battery by shorting leads (A) and
(C) and then close switch SW-1. Re-place
battery if voltage is less than 4.5 volts.
(Heat Sink Mounted Units)
To test SCR’s construct the circuit outlined
in Figure F.15. One 6V lantern battery can
be used. Resistor values are Ò10%. The
voltmeter scale should be low, approximate-
ly 0-5 or 0-10 volts.
1. Connect SCR into the test circuit as
shown (A) lead to anode (C) lead to
cathode and (G) lead to the gate.
2. Close switch SW-1 (switch SW-2 should
open), voltmeter should read zero. If the
voltmeter reads higher than zero the
SCR is shorted.
3. With switch SW-1 closed, close switch
SW-2 for two seconds and release. The
voltmeter should read 3 to 6 volts
before and after switch SW-2 is
released. If the voltmeter does not read,
or reads only while SW-2 is depressed,
the SCR or battery is defective (repeat
Battery Test Procedure).
4. Open switch SW-1, disconnect the gate
lead (G) and reverse the (A) and (C)
leads on the SCR. Close switch SW-1.
The voltmeter should read zero. If the
voltage is higher than zero, the SCR is
shorted.
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F-31
TROUBLESHOOTING & REPAIR
NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM
DC STICK MODE
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
50 volts
This is the typical DC (+) output voltage
waveform generated from a properly operat-
ing machine. Note that each vertical divi-
sion represents 50 volts and that each hori-
zontal division represents 2 milliseconds in
time.
SCOPE SETTINGS
Volts/Div................................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-32
TROUBLESHOOTING & REPAIR
NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM
AC STICK MODE
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
50 volts
This is the typical AC output voltage wave-
form generated from a properly operating
machine. Note that each vertical division
represents 50 volts and that each horizontal
division represents 2 milliseconds in time.
SCOPE SETTINGS
Volts/Div................................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-33
TROUBLESHOOTING & REPAIR
NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM
DC TIG MODE
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
50 volts
This is the typical DC (+) output voltage
waveform generated from a properly operat-
ing machine. Note that each vertical divi-
sion represents 50 volts and that each hori-
zontal division represents 2 milliseconds in
time.
SCOPE SETTINGS
Volts/Div................................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-34
TROUBLESHOOTING & REPAIR
NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM
AC TIG MODE
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
50 volts
This is the typical AC output voltage wave-
form generated from a properly operating
machine. Note that each vertical division
represents 50 volts and that each horizontal
division represents 2 milliseconds in time.
SCOPE SETTINGS
Volts/Div................................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-35
TROUBLESHOOTING & REPAIR
TYPICAL OUTPUT VOLTAGE WAVEFORM - MACHINE LOADED
DC TIG MODE
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
20 volts
MACHINE LOADED TO 200 AMPS AT 50 VDC
This is a typical DC (+) output voltage wave-
SCOPE SETTINGS
form generated from a properly operating
machine. Note that each vertical division
represents 20 volts and that each horizontal
division represents 2 milliseconds in time.
The machine was loaded with a resistance
grid bank. The TIG 255 display read 200
amps at 50VDC.
Volts/Div................................20 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-36
TROUBLESHOOTING & REPAIR
AC TIG MODE (AUTO - BALANCE ON)
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
CH1
0 volts
0 volts
2ms
20 volts
2ms
20 volts
MACHINE LOADED TO 50 AMPS AT 26VAC
MACHINE LOADED TO 200 AMPS AT 46 VAC
These are typical AC output voltage wave-
forms generated from a properly operating
machine. Note each vertical division repre-
sents 20 volts and each horizontal division
represents 2 milliseconds in time. The
machine was loaded with a resistance grid
bank. As the load is increased the output
waveform becomes more “square”.
SCOPE SETTINGS
Volts/Div................................20 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-37
TROUBLESHOOTING & REPAIR
TYPICAL SCR GATE VOLTAGE WAVEFORM
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
5ms
2 volts
This is the typical SCR gate pulse voltage
waveform. The machine was in an open
circuit condition (no load) and operating
properly. Note that each vertical division
represents 2 volts and that each horizontal
division represents 5 milliseconds in time.
SCOPE SETTINGS
Volts/Div..................................2 V/Div.
Horizontal Sweep .................5 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at SCR
gate and cathode: (+) probe to gate, (–)
probe to cathode.
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F-38
TROUBLESHOOTING & REPAIR
ABNORMAL OPEN CIRCUIT VOLTAGE - DC STICK MODE
ONE OUTPUT SCR NOT FUNCTIONING
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
50 volts
This is NOT the typical DC (+) output volt-
age waveform. One output SCR is not
functioning. Note the “gap” in the wave-
form. One SCR gate was disconnected to
simulate an open or non-functioning output
SCR. Each vertical division represents 50
volts and each horizontal division repre-
sents 2 milliseconds in time.
SCOPE SETTINGS
Volts/Div................................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) prove to electrode, (–)
probe to work.
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F-39
TROUBLESHOOTING & REPAIR
ABNORMAL OPEN CIRCUIT VOLTAGE - AC STICK MODE
ONE OUTPUT SCR NOT FUNCTIONING
CAUTION
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
_____________________________________________________________________
CH1
0 volts
2ms
50 volts
SCOPE SETTINGS
This is NOT the typical AC output voltage
waveform. One output SCR is not function-
ing. Note the “gap” in the waveform. One
SCR gate was disconnected to simulate an
open or non-functioning output SCR. Each
vertical division represents 50 volts and
each horizontal division represents 2 mil-
liseconds in time.
Volts/Div................................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling.........................................DC
Trigger.....................................Internal
Note: Scope probes connected at machine
output studs: (+) probe to electrode, (–)
probe to work.
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F-40
TROUBLESHOOTING & REPAIR
FAN MOTOR AND BLADE REMOVAL
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
The following procedure will aid the technician in gaining access to the fan blade and
fan motor, for maintainence or replacement
TOOLS REQUIRED
3/8” socket wrench or nutdriver
10” long screwdriver (slot head)
5/16” open end or box wrench
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F-41
TROUBLESHOOTING & REPAIR
FAN MOTOR AND BLADE REMOVAL (continued)
Fan Baffle
Fan
Mounting
Hardware
Vertical
Bracket
6. The fan blade can be removed by loos-
ening the clamp on the fan blade and
carefully sliding the fan blade off of the
motor shaft. Note: When reinstalling the
fan blade make certain the blade is on
the motor shaft in the correct location.
Approximately .25” past end of shaft.
TEST PROCEDURE
1. Remove main supply power to machine.
2. Remove case sides and top.
3. Locate and SUPPORT rectifier and fan
baffle assembly.
7. If the fan motor is to be removed the
leads to the motor must be disconnect-
ed. The fan motor may be removed by
removing the two #8-32 hex nuts and
associated plain and lock washers that
mount the motor to the vertical bracket.
4. Remove the two self-tapping screws
from the input access door.
5. Remove the five thread-forming screws
holding the fan baffle and rectifier
assembly to the case back. AT THIS
POINT THE RECTIFIER AND FAN
BAFFLE ASSEMBLY WILL DROP
UNLESS SUPPORTED.
Once the baffle assembly and case
back are separated there is sufficient
working space for fan blade and fan
motor removal and replacement.
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F-42
TROUBLESHOOTING & REPAIR
SCR HEAT SINK ASSEMBLY REMOVAL
WARNING
Service and repair should only be performed by Lincoln Electric factory trained person-
nel. Unauthorized repairs performed on this equipment may result in danger to the
technician or machine operator and will invalidate your factory warranty. For your safe-
ty and to avoid electrical shock please observe all safety notes and precautions
detailed throughout this manual.
If for any reason you do not understand the test procedures or are unable to perform
the tests/repairs safely, contact the Lincoln Electric service department for technical
troubleshooting assistance before you proceed call 216-383-2531 or 1-800-833-9353
(WELD).
_____________________________________________________________________
CAUTION
If machine case sides and top are removed the case back and front must be support-
ed. Failure to do this could result in mechanical or electrical damage to the TIG 255.
_____________________________________________________________________
TEST DESCRIPTION
The following procedure will aid the technician in the removal and replacement of
either or both of the two SCR heat sink assemblies.
MATERIALS REQUIRED
7/16” socket and box wrench
1/2" socket and box wrench
9/16” socket and box wrench
ohmmeter (multimeter)
Dow 340 heat sink compound
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F-43
TROUBLESHOOTING & REPAIR
SCR HEAT SINK ASSEMBLY REMOVAL (continued)
SCR Heat
Sink Assemblies
7. Test with an ohmmeter to make certain
TEST PROCEDURE
that the heat sink assembly is electrical-
ly isolated from chassis ground by at
least 500,000 ohms of resistance.
1. Remove main power supply to machine.
2. Remove case sides and top.
3. Locate SCR heat sink assemblies.
8. Reconnect the gate leads.
9. Reconnect the snubber and cable leads
using a thin coating of Dow 340 heat
sink compound on the connection sur-
faces. Be sure that the connection sur-
faces are clean and free from any dirt or
paint.
4. Remove all gate, snubber and cable
leads from the SCR heat sink assembly
that is to be serviced.
5. Remove the four 1/4”-20 hex nuts and
associated plain and lock washers from
the four 1/4”-20x1.75” hex head cap
screws. Remove the heat sink assem-
bly trying not to disturb the insulating
washers and bushings. See figure
above.
6. Reinstall the heat sink assembly in the
same manner being certain that the
insulating washers and bushings are
installed correctly. See figure above.
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F-44
TROUBLESHOOTING & REPAIR
RETEST AFTER REPAIR
Should a machine under test be rejected for
NOTE: 50 Hz machines may be tested
using 60 Hz power.
any reason requiring the removal of any
mechanical part that could affect the
machine’s electrical characteristics, or if any
electrical components are repaired or
replaced, the machine must be retested.
INPUT IDLE AMPS
Input Volts/Hertz
208/60
Maximum Idle Amps
44.0
40.0
47.0
43.0
25.0
230/60
200/50
220/50
380/50
Power Factor
Voltage Across
447-473 VAC
Capacitors
OPEN CIRCUIT VOLTAGES
AC
DC
AC
DC
69 – 73 VAC
69 – 73 VDC
46 – 54 VAC
46 – 54 VDC
Stick Mode OCV
TIG Mode OCV
MAXIMUM ACCEPTABLE OUTPUT VOLTAGE –
AT MINIMUM OUTPUT SETTINGS
TIG Modes
5 Amps @ 12 Volts
MINIMUM ACCEPTABLE OUTPUT VOLTAGE –
AT MAXIMUM OUTPUT SETTINGS
TIG Modes
255 Amps @ 29 Volts
RECOMMENDED METERS FOR MACHINE OUTPUT TESTS
VOLTMETER: AC and DC True RMS Meter – Fluke 8922A or equivalent
AMMETER:
Columbia Type AX AC or DC Tong Ammeter
IMPORTANT: IF OTHER TYPE METERS ARE USED RESULTS MAY NOT BE ACCURATE.
11 / 94
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F-45
TROUBLESHOOTING & REPAIR
RETEST AFTER REPAIR (cont’d)
FIGURE F.16 - TRANSFORMER LEAD TEST POINTS.
MAIN TRANSFORMER SECONDARY VOLTAGES (See Figure F.16)
Test Points
X1 – X2
Voltages
73 – 78 VAC
116 – 122 VAC
217 – 228 VAC
X3 – X4 (230 – 232)
X3 – X5 (230 – 52A)
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Section G
TABLE OF CONTENTS
- ELECTRICAL DIAGRAMS -
Electrical Diagrams .........................................................................................Section G
Control PC Board (G2150) Components...............................................................G-2
Protection Snubber PC Board (L9255) Components.............................................G-6
Wiring Diagram......................................................................................................G-9
Machine Schematic .............................................................................................G-10
Control Board Schematic (G2150).......................................................................G-11
Control Board Schematic(cont’d).........................................................................G-12
Protection/Snubber Board Schematic (l9255) .....................................................G-13
Keypad LED Board (L9212).................................................................................G-14
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G-2
ELECTRICAL DIAGRAMS
CONTROL BOARD (G2150)
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. Individual Printed Circuit Board Components are not avail-
able from Lincoln Electric. This information is provided for reference only. Lincoln Electric discourages
board level troubleshooting and repair since it may compromise the quality of the design and may result in
danger to the Machine Operator or Technician. Improper PC board repairs could result in damage to the
machine.
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G-3
ELECTRICAL DIAGRAMS
CONTROL BOARD (G2150)
Item
Identification
Item
Identification
X12
C22,C32
IC-VOLT REG,FIXED,3-T,(+),1A,5V
CAPACITOR-CEMO,22P,100V,5%
C42
CAPACITOR-ALEL,1000,35V,+30/-20%
R14,R17,R18,R21,R24, RESISTOR-MF,1/4W,100,1%
R26,R109,R154,R155,
C51,C52,C53,C54,
C55,C56,C57,C58,
C59,C60,C82,C83,
C84,C85,C86
CAPACITOR-CEMO,100P,100V,5%
R156,R157,R158,R159,
R160,R162,R163,R168,
R169,R170,R171,R182,
R183*
C5,C20,C25,C34,C41, CAPACITOR-CEMO,.022,50V,20%
C73,C74,C76,C77
R20,R25,R41,R56,R57, RESISTOR-MF,1/4W,1.00K,1%
R68,R69,R74,R77,R84,
R87,R91,R92,R93,R94,
C19,C21
J7
J4
J1
CAPACITOR-CEMO,150P,100V,5%
CONNECTOR,MOLEX,MINI,PCB,4-PIN
CONNECTOR,MOLEX,MINI,PCB,6-PIN
CONNECTOR,MOLEX,MINI,PCB,8-PIN
THERMISTOR-PTC,56 OHMS,90MA
R112,R113,R114,R115,
R118,R120,R123,R124,
R127,R129,R140,R144,
R214,R225,R226,R227,
PTC1,PTC2
R228,R229
R9,R22,R49,R76,R122, RESISTOR-MF,1/4W,10.0K,1%
R125,R128,R172,R187,
R211,R223,R224*
D1,D2,D3,D4,D5,D6,D7, DIODE-AXLDS,1A,400V
D18,D19,D20,D23,D24,
D25,D30,D34,D37,D38,
D39,D40,D41,D43,D44,
D45,D46,D47,D48,D49,
D50,D51,D52,D53,D54,
D55,D56,D57,D58,D59,
D71,D72,D73,D74,D75,
D76,D77,D78,D79,D80,
R39,R44,R67,R199,
R222,R236
R38,R54,R55,R71
R51,R52
R72,R85
R137
RESISTOR-MF,1/4W,100K,1%
RESISTOR-MF,1/4W,1.00M,%
RESISTOR-MF,1/4W,150,1%
RESISTOR-MF,1/4W,1.50K,1%
RESISTOR-MF,1/4W,15.0K,1%
D81,D92,D99,D100,D101
R50,R101,R134,R212 RESISTOR-MF,1/4W,2.21K,1%
R27,R63,R142
RESISTOR-MF,1/4W,221K,1%
L1
CHOKE-330UH,10%,110MA,MOLDED
L2,L3
C16,C35
CHOKE-390UH,5%,225MA,CONFORMAL
CAPACITOR-TAEL,18,15V,10%
R12,R23,R64,R106,
R107,R108,R181,R184,
R185
RESISTOR-MF,1/4W,267,1%
C23,C44,C47,C48,C71 CAPACITOR-TAEL,1.0,35V,10%
C43
CAPACITOR-ALEL,20,50V,+75/-10%
CAPACITOR-TAEL,27,35V,10%
C27,C28,C29,C30
R34
R138,R139
RESISTOR-MF,1/4W,2.67K,1%
RESISTOR-MF,1/4W,26.7,1%
OCI1,OCI2,OCI3,
OCI4,OCI5,OCI6*
OPTOCOUPLER-PHOTO-Q,70V,
CNY17-3
R88,R143,R146,R147, RESISTOR-MF,1/4W,3.32K,1%
R148,R149,R150,R151,
R152,R153,R166,R167
X16
IC-VOLT REG,FIXED,3-T,(-),1A,15V
R141
R73,R75,R82,R83,
R102,R103,R104*
RESISTOR-MF,1/4W,33.2K,1%
RESISTOR-MF,1/4W,475,1%
C3,C7,C10,C11,C12, CAPACITOR-CEMO,0.1,50V,10%
C14,C15,C33,C38,
C45,C62,C69,C70,
C72,C75,C78,C81
R42,R48,R53,R66,
R79,R81,R97,R130,
R131,R132,R201,R202,
R203,R204,R205,R206,
R207,R208,R209,R210,
R213,R215,R216,R217,
R218
RESISTOR-MF,1/4W,4.75K,1%
J5
J8
J6
CONNECTOR,MOLEX,MINI,PCB,10-PIN
CONNECTOR,MOLEX,MINI,PCB,12-PIN
CONNECTOR,MOLEX,MINI,PCB,14-PIN
ZENER DIODE-1W,30V,5%,1N4751A
ZENER DIODE-1W,18V,5%,1N4746A
DZ1,DZ6,DZ7,DZ10
DZ4,DZ5,DZ8,DZ9
Q1,Q3,Q5,Q8,Q10,
Q11,Q13,Q14,Q16,Q17
TRANSISTOR-N,T226,0.5A,40V,2N4401
R28,R29,R30,R31,
R32,R40
R16,R19,R43,R65,
R70,R116,R136,R200
RESISTOR-MF,1/4W,47.5K,1%
RESISTOR-MF,1/4W,475K,1%
Q2,Q4,Q6,Q12
D42
TRANSISTOR-NMF,4PDIP,1A,100V,
RFD110
DIODE-AXLDS,1A,30V,SCHOTTKY
CONT’D ON REVERSE PAGE
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. Individual Printed Circuit Board Components are not avail-
able from Lincoln Electric. This information is provided for reference only. Lincoln Electric discourages
board level troubleshooting and repair since it may compromise the quality of the design and may result in
danger to the Machine Operator or Technician. Improper PC board repairs could result in damage to the
machine.
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G-4
CONTROL BOARD (G2150) (cont’d)
ELECTRICAL DIAGRAMS
Item
Identification
X19
X10
IC-UNDERVOLTAGE-SENSING,RESET,
MCU
IC-CMOS,INVERTER,SCHMITT,
HEX,HC14A
C65,C66
X11,X14
C49,C67,C68
DZ13,DZ14,DZ15,
DZ16,DZ17
J2
CAPACITOR-TAEL,4.7,35V,10%
IC-OP-AMP,QUAD,HIGH-PERF,33074A
CAPACITOR-CD,.0047,3000V,20%
ZENER DIODE-1W,12V,5%,1N4742A
CONNECTOR,PCB,WW,MALE,DIL,1X9
REGULATOR & HEATSINK ASBLY
DIODE-AXLDS,1A,1000V
CAPACITOR-CD,750P,1000V,10%
RESISTOR-MF,1/4W,301,1%
CRYSTAL-QUARTZ,8.000MHZ
OPTOCOUPLER-TRIAC DRIVER,ZVC,
3083
X15
D10,D11,D21,D22
C79,C80
R33
Y1
OCI8,OCI9,OCI10
X20,X21,X22
IC-CMOS,LATCH,3-STATE,OCTAL,
HC573A
TRI1,TRI2,TRI3
R237
X31,X32
R164,R235
R7
R230,R231,R232,
R233,R234
TRIAC-T220,6A,800V
TRIMMER-MT,1/2W,10K,10%,LINEAR
IC-ARRAY,CLAMPING,PERIPHERAL
RESISTOR-WW,5W,150,5%,SQ
RESISTOR-MF,1/4W,133K,1%
RESISTOR-MF,1/4W,26.7K,1%
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. Individual Printed Circuit Board Components are not avail-
able from Lincoln Electric. This information is provided for reference only. Lincoln Electric discourages
board level troubleshooting and repair since it may compromise the quality of the design and may result in
danger to the Machine Operator or Technician. Improper PC board repairs could result in damage to the
machine.
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G-5
NOTES
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G-6
PROTECTION/SNUBBER BOARD (L9255)
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. Individual Printed Circuit Board Components are not avail-
able from Lincoln Electric. This information is provided for reference only. Lincoln Electric discourages
board level troubleshooting and repair since it may compromise the quality of the design and may result in
danger to the Machine Operator or Technician. Improper PC board repairs could result in damage to the
machine.
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G-7
PROTECTION/SNUBBER BOARD (L9255)
Item
Identification
C23,C24,C25,C26
J15
J14
CAPACITOR-CEMO,4700P,50V,10%
CONNECTOR,MOLEX,MINI,PCB,6-PIN
CONNECTOR,MOLEX,MINI,PCB,8-PIN
L1,L2,L3,L4,L5,L6,L7, CHOKE-390UH,5%,225MA,CONFORMAL
L8,L9,L10,L11
R1,R2,R3,R4
RESISTOR-CC,2W,47,10%
J11
J10
J12
J13
CONNECTOR,MOLEX,MINI,PCB,10-PIN
CONNECTOR,MOLEX,MINI,PCB,12-PIN
CONNECTOR,MOLEX,MINI,PCB,14-PIN
CONNECTOR,MOLEX,MINI,PCB,16-PIN
C1,C2,C3,C4,C5,C6,
C7,C8,C9,C10,C11,
C12,C13,C14,C15,
C16,C17,C18,C29
CAPACITOR-CD,.0047,3000V,20%
C19,C20,C21,C22
CAPACITOR-PEF,0.68,400V,10%
L12,L13,L14,L15,L16 CHOKE-RF,390UH,10%,1A,SLEEVED
TP1,TP2,TP3,TP4
TP5
C27,C28
R5,R6
MOV-150VRMS,45J,14MM
MOV-320VRMS,160J,20MM
CAPACITOR-PEF,0.1,400V,10%
RESISTOR-MF,1/4W,26.7,1%
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. Individual Printed Circuit Board Components are not avail-
able from Lincoln Electric. This information is provided for reference only. Lincoln Electric discourages
board level troubleshooting and repair since it may compromise the quality of the design and may result in
danger to the Machine Operator or Technician. Improper PC board repairs could result in damage to the
machine.
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
G-8
NOTES
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
G-9
ELECTRICAL DIAGRAMS
WIRING DIAGRAM - SQUARE WAVE TIG 255
TO GROUND PER NATIONAL ELECTRIC CODE
PIEZO
BUZZER
(+)
(-)
X1
C1
235
236
R3
TO KEYPAD MATRIX
236A
C2
R4
239
238A
(2,2)
(2,1)
(3,1)
238
237
240
(4,2)
(5,2)
(4,1)
(5,1)
230E
(1,2)
(1,1)
50/60 HZ
MACHINES ONLY
(1,3)
230D
231
229
232B
230B
229A
230C
230
232
52A
C-RW
R
G2719
CLEVELAND, OHIO U.S.A.
NOTE: This diagram is for reference only. It may not be accurate for all machines covered by this manual. The specific
diagram for a particular code is pasted inside the machine on one of the enclosure panels.
SQUARE WAVE TIG 255
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G-10
ELECTRICAL DIAGRAMS
MACHINE SCHEMATIC — SQUARE WAVE TIG 255
MAIN
TRANSFORMER
C8
C9
RECONNECT
PANEL
H5
T1
.0047/
3KV
H4
L2
H3
H2
X1
X2
SCR4 CATHODE (MAIN RECTIFIER AC1)
SCR4 GATE
SCR4 CATHODE
10J10
4J10
216A
9J11
9J5
4J5
1J5
SCR4 GATE
G4
4J11
1J11
INPUT
LINES
SCR4
SCR1 GATE
SCR2 GATE
SCR3 GATE
SCR3 CATHODE
SCR1
SCR1 GATE
2J11
3J11
8J11
6J11
1J10
12J10
2J10
2J5
3J5
8J5
6J5
G1
G2
MAIN RECTIFIER
SCR2 GATE
-
L1
MAIN
H1
220A
+
-
RECTIFIER
D1
150
SCR1
&
SCR2 CATHODE
P
R
/400
SCR3
SCR2
SCR3 GATE
SCR3 CATHODE (MAIN RECTIFIER AC2)
3J10
9J10
7J10
G3
H1
217A
304
SCR1
&
SCR2 CATHODE (MAIN RECTIFIER +)
218A
AC/DC MICROSWITCH
AC/DC MICROSWITCH
AC/DC MICROSWITCH
4J13
12J13
C4
50/460
C5
4J12
11J12
5J12
4J6
P
C
O
N
T
OUTPUT
INDUCTOR
AC/DC MICROSWITCH
ELECTRODE SENSE
312
11J6
5J6
L1
O
T
E
C
T
I
ELECTRODE SENSE
WORK SENSE
WORK SENSE
305
5J13
13J13
12J12
2J12
8J12
1J12
3J12
10J12
12J6
2J6
C
SHUNT
REMOTE CONTROL HIGH
REMOTE CONTROL WIPER
REMOTE CONTROL LOW
ARC START SWITCH
313C
400A/200mV
SHUNT (-)
SHUNT (+)
250
8J6
1J6
SEE NOTE
A
REMOTE
RECEPTACLE
3J6
ARC START SWITCH
10J6
U
A
B
2J13
9J13
DC
302
309
301
311
303
REMOTE
B
O
A
R
D
CURRENT
CONTROL
N
10K
T2
3J8
TM
B
R
B
C
D
E
1J13
OPTIONAL AMPTROL REMOTE
24VAC
AC
DC
AC
B
9J8
1J8
CONTROL AND ARC START SWITCH
11J13
R
REMOTE
18VAC
18VAC
ARC START
SWITCH
8J14
4J14
432
433
7J8
W
W
3J13
S2A
AC
AC
115VAC
2J8
6J8
R
-
F
+
-
+
DC
NO CONNECTION
DC
DC
DC
O
16VAC
12J8
5J8
O
POLARITY
SWITCH
S2
U
16VAC
O
N
U
11J8
50/100
R1
R
O
L
CLOSED
IN DC
4J8
Y
16VAC
10J8
Y
3J15
2J15
6J15
1J15
236
237
233
C1
115VAC FOR HI-FREQ
HI-FREQ CONTROL1
3J14
2J14
6J14
3J4
2J4
5J4
1J4
4J4
432B
436
235
229
R2
435
429
4/220
HI-FREQ CONTROL
2
25/25
115VAC FOR SOLENOIDS
115VAC FOR SOLENOIDS
1J14
5J14
5J15
4J15
432A
232A
SHUNT (-)
SHUNT (+)
2J7
1J7
R
222
W
221
SHUNT TOROID L2
(-)
6J6
BYPASS
PC BOARD
PIEZO
BUZZER
HIGH
VOLTAGE
TRANSFORMER
(+)
P
13J6
T3
.0015/
12KV
R4
200/100
R3
200/100
C3
239A
LED(+)
C
1J3
LED(-)
D0
2J3
9J3
L3
L4
S
F
235A
D1
SPARK
GAP
HIGH FREQ.
TRANSFORMER
10J3
11J3
12J3
13J3
14J3
15J3
16J3
4J3
5J3
7J3
3J3
6J3
8J3
D2
D3
D4
D5
15/250
C2
NOTE A:
LEAD #250 FROM POWER FACTOR CAPACITORS
CONNECTS ACCORDING THE THE INPUT VOLTAGE
LCD
T4
D6
D7
233A
240
208/230/460, 200/380/440
DISPLAY
HIGH
VDD
Vo
FREQUENCY
CIRCUIT
LEAD #250 CONNECTS TO "HIGH" TERMINAL ON
RECONNECT PANEL, ALONG WITH CORRECT LEAD
FROM MAIN TRANSFORMER (T1)
B
O
A
R
D
R/W
VSS
RS
PL1
E
200/240/400, 220/380/415. 380/415/500
230E
LEAD #250 CONNECTS TO THE H5 LEAD OF
THE MAIN TRANSFORMER (T1)
WORK
ELECTRODE
ROW
ROW
ROW
1
1J9
2J9
3J9
1J1
2J1
3J1
4J1
5J1
6J1
7J1
8J1
2
3
230/460/575
LEAD #250 CONNECTS TO THE "MID" TERMINAL
ON THE RECONNECT PANEL, ALONG WITH THE
H3 LEAD FROM THE MAIN TRANSFORMER (T1)
KEYPAD LED
PC BOARD
4J9
5J9
229A
COL
COL
COL
COL
4
3
2
1
6J9
7J9
8J9
GAS
SOLENOID
WATER
SOLENOID
SV1
SV2
ELECTRICAL SYMBOLS PER E1537
230B
230C
LEAD COLORING CODE:
COMPONENT VALUE
UNITS:
ROW
1
2
CB1
1J2
B-BLACK
G-GREEN
O-ORANGE
R-RED
115V/15A
ROW
3J2
5J2
7J2
CAPACITORS:
MFD/VOLTS
231
230
ROW
ROW
3
4
X3
230D
U-BLUE
RESISTORS:
FAN
ROW
5
W-WHITE
OHMS/WATTS
9J2
115 VAC
232B
Y-YELLOW
X4
X5
RECEPTACLE
232
C8
KEYPAD
COL
COL
1
2J2
4J2
CONNECTOR PIN NUMBERS:
EXAMPLE: THIS PIN IN
CONNECTOR J10 IS "6J10"
C7
.22/400V
220V
RECEPTACLE
CB2
220V/2A
2
.22/400V
COL
COL
3
4
6J2
8J2
1
2
3
8
51
52
52A
230E
9
16
LATCH
1 2
3
16
50/60HZ MACHINES ONLY
VIEW OF CONNECTOR ON PC BOARD
SQUARE WAVE TIG 255
A
SCHEMATIC
-
MACHINE
3-10-94
2736
G
NOTE: This machine schematic is provided for reference only and may not be totally applicable to every code covered in this manual.
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
G-11
ELECTRICAL DIAGRAMS
CONTROL BOARD SCHEMATIC — SQUARE WAVE TIG 255
(G2150)
TO A482.2
R136
475K
R137
15.0K
R67
100K
D30
ELECTRODE
-15V
J6
13
12
5
R55
14
D22
D11
D21
D10
1.00M
X11
R39
LEGEND
C49
.0047
3000V
100K
NGND
(GROUND AND +5V NETS)
C79
750p
1000V
Voltage FB
WORK
IOGND
PROCESSOR IO COMMON
D76
R40
47.5K
NGND
LGND
NGND
LOGIC COMMON
NOISY COMMON
NGND
2
VOLT_FB
12
R38
1.00M
J6
1
X11
R69
C80
750p
1000V
J8
3
6
AUX SCR1,2
16VAC
5
LCDGND
X31GND
DISPLAY COMMON
X31 COMMON
1.00K
D54
D49
D51
C81
0.1
50V
+15V
1
+15V
1
DZ16
12V
1W
DZ14
12V
1W
D77
X31
47.5K
NGND
X32GND
X32 COMMON
(
1
of
5
XFMR
secondary
100
100
100
100
100
100
5
5
4
C28
27
35V
windings
)
D53
C29
27
35V
IOGND
NGND
IO+5V
PROCESSOR IO+5V SUPPLY
LOGIC +5V SUPPLY
NOISY+5V SUPPLY
DISPLAY +5V SUPPLY
X31 +5V SUPPLY
IO+5V
J8
DZ17
12V
1W
DZ15
12V
1W
AUX SCR1,2
12
OCI4
CNY17-3
L+5V
OCI5
2
6
4
2
6
CNY17-3
N+5V
DZ7
30V
1W
DZ10
30V
1W
NGND
NGND
4.75K
LCD+5V
X31_+5V
X32_+5V
Q4
1A
100V
Q2
1A
100V
9
8
ZERO CROSS
Q1
600mA
40V
X10
J5
J5
J5
1.00K
1.00K
SCR
SCR
2
2
GATE
DZ4
18V
1W
1
DZ8
18V
1W
2
7
SCR
SCR
1
GATE
X32 +5V SUPPLY
1.00K
R214
1.00K
D52
D59
R199
100K
D58
D50
1.00K
D99
C65
4.7
35V
C41
D100
N+5V
L+5V
IO+5V
LCD+5V
X31_+5V
X32_+5V
475K
J5
J8
CATHODE
6
1
CATHODE
C66
IO+5V
4.7
35V
D101
IOGND
J8
+15V
5
C38
.1
50V
AUX SCR3
16VAC
4
AUX SCR4
16VAC
D48
D45
D47
1.00K
D55
D1
+15V
1
+15V
1
D25
D23
Q5
600mA
40V
3
4
(
1
of
5
XFMR
(
1
of
5
XFMR
X10
R184
267
secondary
100
100
100
5
secondary
100
100
100
windings
)
5
D46
windings
)
C27
27
35V
D6
Q17
600mA
40V
D56
IN
OUT
C30
S18647-2
R27
R22
10K
D5
D4
27
35V
X12
7805
J8
AUX SCR3
X15
J8
11
IN
OUT
221K
AUX SCR4
10
7815
OCI3
2
6
4
OCI6
4
J8
IOGND
2
6
CNY17-3
1
CNY17-3
GND
GND
2.21K
D72
C44
1.0
35V
DZ6
C67
.0047
3000V
C42
35V
1000
C47
30V
1W
DZ1
30V
1W
1.0
D71
IOGND
Q6
1A
100V
Q12
1A
100V
35V
IOGND
J8
CT
J5
7
J5
3
36VAC CT
SCR
3
GATE
1.00K
SCR
SCR
4
4
GATE
DZ5
18V
1W
4
C43
C68
.0047
3000V
D44
DZ9
18V
1W
(
1
of
5
XFMR
20
50V
C48
1.0
35V
D7
secondary
GND
D43
1.00K
windings
)
D57
D73
1.00K
J8
IO+5V
2
J5
X16
7915
SCR
3CATHODE
J5
8
IN
OUT
9
D3
D2
CATHODE
C45
.1
50V
1.00K
D92
D24
Q3
600mA
40V
1
2
X10
R185
267
NGND LGND
-15V
VB
LCDGND
X31GND
X32GND
Q16
600mA
40V
R63
R9
IOGND
221K
10K
IOGND
IOGND
16VAC
16VAC
L+5V
11
10
6
X10
GENERAL INFORMATION
+15V
IOGND
X31_+5V
X32_+5V
6
CAPACITORS
RESISTORS
DIODES
=
MFD
(
.022/50V
1/4W UNLESS OTHERWISE SPECIFIED)
(UNLESS OTHERWISE SPECIFIED)
UNLESS OTHERWISE SPECIFIED)
5
X10
X10
=
Ohms
(
X31
=
1A, 400V
16VAC
24VAC
10K
26
20
14
20
Vdd
20
120VAC
4
4
8
8
C11
0.1
50V
C14
0.1
50V
13
12
7
10K
C3
0.1
50V
X3
X10
C10
0.1
50V
C7
0.1
50V
C70
0.1
50V
C69
0.1
50V
X20
X21
X22
74HC14
X11
X14
SQUARE WAVE TIG 255 CONTROL BOARD
01/03/94
X31
X32
X31
MC68HC11
74HC573
10
74HC573
10
74HC573
10
10K
C12
0.1
50V
C15
0.1
50V
TCF6000
TCF6000
33074A
11
33074A
11
Vss
1
A482.1
7
1
1
7
A
IOGND
36VAC C.T.
IOGND
X32
X31GND
X32GND
LGND
LGND LGND LGND
-15V
CONTROL TRANSFORMER
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. This Printed Circuit Board schematic is provided for reference only. It may not
be totally applicable to your machine's specific PC board version. This diagram is intended to provide general information
regarding PC board function. Lincoln Electric discourages board level troubleshooting and repair since it may compromise
the quality of the design and may result in Danger to the Machine Operator or Technician. Improper PC board repairs
could result in damage to the machine.
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
G-12
ELECTRICAL DIAGRAMS
CONTROL BOARD SCHEMATIC — SQUARE WAVE TIG 255 (cont’d)
(G2150)
IO+5V
N+5V
J4
J4
J4
5
2
3
R106
267
R102
475
1
6
4
MT2
MT1
J6
4
OCI8
TRI1
J2
J2
J2
J2
10K
COL
COL
COL
COL
1
2
4
6
8
G
1.50K
D37
D20
475
2
Q13
600mA
40V
KEYPAD
R122
10K
2
R227
J2
J2
J2
J2
J2
ROW
ROW
ROW
ROW
ROW
1
1
1
5
1.00K
Q14
600mA
40V
AC/DC
MICROSWITCH
2
IOGND
1
3
5
7
9
R125
10K
C34
OCI1
CNY17-3
3
4
3
4
5
1K
Q8
600mA
40V
R107
267
HIGH
FREQ
R103
475
2
6
4
R128
10K
6
4
MT2
MT1
C35
18
15V
OCI9
TRI2
Q11
600mA
40V
C21
150p
50V
D19
D18
G
R172
10K
115V
2
475
L+5V
R228
J8
IO+5V
1.00K
C82
C83
C84
C85
C86
3
IOGND
1
100p
100V
100p
100V
100p
100V
100p
100V
100p
100V
24VAC
J4
IOGND
NGND
NGND
NGND
NGND
NGND
IOGND
(
1
of
5
XFMR
1
R108
267
475
secondary
R104
475
1.50K
D38
D40
6
4
WATER
windings
)
GAS
J8
MT2
MT1
9
OCI10
TRI3
CRYSTAL
L+5V
G
D0-D7
J6
J6
1
5
4
115V
1
1
2
C22
22p
100V
C25
OCI2
CNY17-3
X32
X32
X32
X32
X32
RESET
J4
2
3
4
5
6
4
R229
1K
8.0MHz
130
Y1
1.00M
1K
1.00K
2
6
10
2
3
4
5
6
7
8
9
19
18
17
16
15
14
13
12
D0
D1
D0
D1
Q0
Q1
IOGND
C32
C16
18
15V
A/D
REF
74HC573
X21
22p
C19
150p
50V
100V
ARC START
SWITCH
IN
D39
D34
475
D2
D3
D4
D5
D6
D7
D2
D3
Q2
Q3
Q4
Q5
Q6
Q7
C33
0.1
50V
RES
X19
GND
D75
J6
C23
1.0
35V
3
C20
LGND
D4
D5
D6
D7
PIEZO
BUZZER
J6
J6
C5
1
_
52
13
+
6
+15V
Vss
VRH
VRL
7
8
2
51
17
14
EXTAL
XTAL
LGND
N+5V
L2
RESET
PC5
PC2
PC0
PC1
J3
LATCH OUTPUT ENABLE
MISC. LATCH ENABLE
DISPLAY LATCH ENABLE
LED LATCH ENABLE
NOT USED
LED(-)
+15V
VB
2
+15V
IOGND
MODB
XIRQ
2.21K
R101
.39mH
Q10
600mA
40V
18
1
1
1
1
1
LE
D74
OE
19
X3
9
150
5W
IRQ
1.00K
D80
R235
ROW
ROW
5
4
24
10
44
46
48
30
3
LCD+5V
PD4
PD3
PD2
PD1
PD0
PA7
PD5
PE2
PE1
L3
J3
23
PTC2
PE4
R164
150
1
IOGND
LED(+)
J6
2
ROW
ROW
ROW
3
2
NOT USED
.39mH
22
21
PE5
5W
NGND
+
t
D79
NOT USED
D78
IOGND
L1
PE6
56
D81
1.00K
1
NOT USED
20
OC4
AC/DC MICROSWITCH
ARC START SWITCH
NOT USED
.33mH
27
25
47
45
43
49
32
29
28
16
MODA
NOT USED
4
REMOTE
CONTROL
POT
STRA/AS
NGND
REMOTE CURRENT
NOT USED
5
ECLOCK
STRB/R/W
PC3
LOW CURRENT FEEDBACK
HIGH CURRENT FEEDBACK
VOLTAGE FEEDBACK
ZERO CROSS
NOT USED
NGND
6
10K
12 NOT USED
13 NOT USED
2
3
4
5
6
7
8
9
19
100
100
100
100
J3
J3
J3
J3
J3
J3
J3
J3
D0
D1
D0
Q0
Q1
J6
J6
3
2
PE0
PE3
IC1
R154
R156
R158
R160
9
D0
D1
8
74HC573
X22
R53
R66
18
17
16
15
14
13
12
100
100
100
100
D1
D2
D3
REM CUR
1
PC4
R155
10
4.75K
4.75K
R41
X14
NOT USED
31
LCD
D2
D3
D4
D5
D6
D7
Q2
Q3
Q4
Q5
Q6
Q7
1.00M
2
OC5
1
1
D2
D3
D4
D5
D6
D7
C71
1.00K
DZ13
12V
1W
SCR 2,4
SCR 1,3
42
C72
0.1
50V
D0
13.05V
DISPLAY
OC3
OC2
PC7
PC6
PE7
PA1
PBO
R157
R159
R109
12
13
14
15
16
D0-D7
PTC1
+
41
X31
D1
D4
D5
D6
D7
PB1
1
DISPLAY
E
40
D2
PB2
t
DISPLAY RS
15
39
D3
56
IOGND
PB3
NOT USED 50
NOT USED 33
38
D4
NGND
NGND
PB4
37
36
35
D5
D6
D7
PB5
100p
C51
100V
100p
C52
100V
100p
C53
100V
100p
C54
100V
100p
C55
100V
100p
C56
100V
100p
C57
100V
100p
C58
100V
NOT USED 34
26
PA0
Vdd
PB6
1
1
1
LE
5
6
LGND
R138
OE
LO_ CUR_FB
PB7
LCD CONTRAST TEMPERATURE COMPENSATION CIRCUIT
7
MC68HC11
J3
J3
J3
26.7
R144
1.00K
X11
3
7
5
VSS
R/W
Vo
-15V
R88
3
D0-D7
R139
26.7
R34
3.32K
C75
0.1
50V
LGND
2.67K
C73
LCDGND
X31
6
5
R33
301
R143
3.32K
J1
J1
J1
J1
33.2K
2
3
4
5
6
7
8
9
19
18
17
16
15
14
13
12
D0
D1
D0
D1
Q0
Q1
8
7
6
5
7
74HC573
X20
TP3
X14
TP1
N+5V
IOGND
R97
4.75K
C74
D2
D3
D4
D5
D6
D7
D2
D3
Q2
Q3
Q4
Q5
Q6
Q7
LCDGND
LCD+5V
9
D4
D5
D6
D7
R130
NGND
J3
8
4.75K
X14
4
VDD
221K
10K
TP2
10
30V
R131
C62
D0-D7
1.0A
4.75K
D42
0.1
J1
J1
J1
J1
LGND
133K
+
-
4
3
2
1
J7
R91
50V
10
9
LCDGND
1
R52
150
R7
HI_ CUR_FB
1
1
1
LE
1.00K
8
R68
X11
OE
CW
R92
4
1.00K
J7
13
12
1.00K
LCD CONTRAST CIRCUIT
10K
MT
LCDGND
R236
100K
C78
0.1
50V
1.00K
14
X14
X31
R93
2
R51
150
R50
1.00K
2.21K
SHUNT
400A/200mV
LCDGND
R94
C76
C77
NGND
IOGND
1.00K
LCDGND
100
J3
J3
R162
6
RS
E
R166
3.32K
100
NGND
R163
8
R167
100p
C59
100p
C60
3.32K
100V
100V
LEGEND
(GROUND AND +5V NETS)
LCDGND
TO A482.1
IOGND
PROCESSOR IO COMMON
LGND
NGND
LOGIC COMMON
NOISY COMMON
GENERAL INFORMATION
LCDGND
X31GND
DISPLAY COMMON
X31 COMMON
CAPACITORS
RESISTORS
DIODES
=
MFD
(
.022/50V
UNLESS OTHERWISE SPECIFIED)
UNLESS OTHERWISE SPECIFIED)
=
Ohms
(
1/4W
=
1A, 400V
(UNLESS OTHERWISE SPECIFIED)
X32GND
X32 COMMON
IO+5V
PROCESSOR IO+5V SUPPLY
LOGIC +5V SUPPLY
NOISY+5V SUPPLY
DISPLAY +5V SUPPLY
X31 +5V SUPPLY
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
SQUARE WAVE TIG 255 CONTROL BOARD
L+5V
01/03/94
A
N+5V
repairs will invalidate your factory warranty. This Printed Circuit Board schematic is provided for reference only. It may not
be totally applicable to your machine's specific PC board version. This diagram is intended to provide general information
regarding PC board function. Lincoln Electric discourages board level troubleshooting and repair since it may compromise
the quality of the design and may result in Danger to the Machine Operator or Technician. Improper PC board repairs
could result in damage to the machine.
A482.2
LCD+5V
X31_+5V
X32_+5V
X32 +5V SUPPLY
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
G-13
ELECTRICAL DIAGRAMS
PROTECTION/SNUBBER BOARD SCHEMATIC — SQUARE WAVE TIG 255
(L9255)
A
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. This Printed Circuit Board schematic is provided for reference only. It may not
be totally applicable to your machine's specific PC board version. This diagram is intended to provide general information
regarding PC board function. Lincoln Electric discourages board level troubleshooting and repair since it may compromise
the quality of the design and may result in Danger to the Machine Operator or Technician. Improper PC board repairs
could result in damage to the machine.
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
G-14
ELECTRICAL DIAGRAMS
KEYPAD LED BOARD — SQUARE WAVE TIG 255
(L9212)
NOTE: Lincoln Electric assumes no responsibility for liabilities resulting from board level troubleshooting. PC Board
repairs will invalidate your factory warranty. This Printed Circuit Board schematic is provided for reference only. It may not
be totally applicable to your machine's specific PC board version. This diagram is intended to provide general information
regarding PC board function. Lincoln Electric discourages board level troubleshooting and repair since it may compromise
the quality of the design and may result in Danger to the Machine Operator or Technician. Improper PC board repairs
could result in damage to the machine.
SQUARE WAVE TIG 255
Download from Www.Somanuals.com. All Manuals Search And Download.
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