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SQUARE WAVE TIG 255
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F-5
TROUBLESHOOTING & REPAIR
TROUBLESHOOTING GUIDE
Observe Safety Guidelines
detailed in the beginning of this manual.
PROBLEMS
(SYMPTOMS)
115VAC Receptacle not working
properly (voltage is below 108VAC).
Machine has welding output - fan is
running.
Machine regularly overheats - ther-
mostat opens, PL1 (yellow light on
front panel) glows. The fan runs
but machine has no output and no
display.
Machine makes a very loud
buzzing noise in DC Stick Mode, or
in DC TIG Mode when the arc start
or amptrol is pressed.
There is no current draw from
machine’s output studs.
(The machine is not externally
loaded).
POSSIBLE AREAS OF
MISADJUSTMENT(S)
1. Check for 115VAC at
receptacle - if low (below
108VAC), then check input
voltage to machine.
1. Welding application may
exceed recommended duty
cycle.
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.
1. Inspect output stud insulators
for cracks or signs of over-
heating.
RECOMMENDED
COURSE OF ACTION
1. If voltage at the receptacle is
zero, then check for open cir-
cuit breaker (CB1)
2. Check leads #230, #231, and
#232 for loose or broken con-
nections. Refer to wiring dia-
gram.
1. Check for proper fan operation.
2. The thermostat may be faulty -
Should be normally closed
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.
3. Check the polarity switch (S2)
for correct connections.
OUTPUT PROBLEMS
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