Lincoln Electric Precision TIG 375, Service Manual, Page: 59 / 143

F-13 F-13
PRECISION TIG 375
TROUBLESHOOTING & REPAIR
TROUBLESHOOTING GUIDE
Observe Safety Guidelines
detailed in the beginning of this manual.
PROBLEMS
(SYMPTOMS) POSSIBLE AREAS OF
MISADJUSTMENT(S) RECOMMENDED
COURSE OF ACTION
TIG WELDING PROBLEMS
The high frequency “spark” is pre-
sent at the tungsten electrode, but
the operator is unable to establish
a welding arc. The machine has a
normal open circuit voltage. Refer
to Technical Specifications in the
Installation section.
1. The torch may be faulty. Check
or replace.
2. The current control may be set
too low.
3. The tungsten electrode may be
contaminated. Replace or
sharpen.
4. The electrode may be too large
for the process.
5. If a helium blend is being used
as a shielding gas, reduce the
percentage of helium.
6. Check the welding cables for
loose or faulty connections.
1. Check spark gap adjustment.
See the Maintenance Section.
2. This may be a welding proce-
dure problem.
When AC TIG welding, the arc is
erratic and there is a loss of “clean-
ing” of the work piece.
1. The tungsten electrode may be
small for the process. Use a larg-
er diameter tungsten or a pure
tungsten.
2. If a helium blend is used as a
shielding gas, reduce the per-
centage of helium.
3. Check the balance control set-
ting.
1. Check components R5 and C7 in
the high voltage transformer pri-
mary circuit.
2. Perform the SCR Bridge Test .
Arc “pulsates” in AC polarity. DC
TIG is OK.
1. Check that the machine controls
are set correctly for the process.
1. Micro switch S2A may be faulty.
It should “open” in the AC mode.
See the Wiring Diagram.
Retur
n
to
Section
T
OC
Retur
n
to
Section
T
OC
Retur
n
to
Section
T
OC
Retur
n
to
Section
T
OC
Retur
n
to
Master
T
OC
Retur
n
to
Master
T
OC
Retur
n
to
Master
T
OC
Retur
n
to
Master
T
OC
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely, con-
tact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed.
Call 1-888-935-3877.