E-7
TROUBLESHOOTING
E-7
SQUARE WAVE TIG 275
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact your
Local
Lincoln Authorized Field Service Facility
for technical troubleshooting assistance before you proceed.
CAUTION
PC BOARD TROUBLESHOOTING
PROCEDURE
Before replacing a PC Board which is suspected of being
defective, visually inspect the PC Board in question for any
electrical or mechanical damage to any of the components or
conductors on the board, partially insulated molex pins or
connectors.
a. If there is no visible damage to the PC Board, install a new
one and see if this remedies the problem. If the problem
is remedied, reinstall the old PC Board to see if the prob-
lem still exists. If the problem no longer exists with old PC
Board:
1. Check the PC Board harness connector pins for
corrosion, contamination or looseness.
2. Check leads in the plug harness for loose or
intermittent connections.
b. If PC Board has visible electrical damage, before possibly
subjecting the new PC Board to the same cause of failure,
check for possible shorts, opens or grounds caused by:
1. Frayed or pinched lead insulation.
2. Poor lead termination, such as a poor contact or
a short to adjacent connection or surface.
3. Shorted or open control cable leads, or other
external leads.
4. Foreign matter or interference behind the PC
Boards.
c. If PC Board has visible mechanical damage, inspect for
cause, then remedy before installing a replacement PC
Board.
If there is damage to the PC Board or if replacing PC
Board corrects problem, return it to the local Lincoln
Electric Field Service Shop.
INPUT - BYPASS PC BOARD
(EUROPEAN
MODELS ONLY)
This board is mounted to the case front and connects
to the input power at the line switch. It passes excess
high frequency to ground, protecting the machine and
power line. For proper operation it must be securely
grounded, by means of its ground and mounting
screws to the case front. The quick connect terminals
from the line switch must be fully seated. Failures of
this board should be very rare.
BYPASS / STABILIZER PC BOARD
The board is mounted between the output terminals. It
passes excess high frequency to ground before it can
reach the inside of the machine. For proper operation,
it must be securely grounded, by means of its ground
and mounting screws, to the case front. Failures of this
board should be very rare.
DISPLAY PC BOARD
The board is mounted directly to the front panel. The
Control P.C. Board supplies power and metering infor-
mation to the board.
CONTROL PC BOARD
This board, located on the left divider assembly, is the
heart of the machine. All welding output is controlled
by this board. The Display board receives its informa-
tion from the Control board as well. Very little external
diagnostic work can be performed on this board. If one
control or function of the machine does not appear to
be working, it is best to trace out the wiring associated
with that function all the way back to the Control board
with an ohmmeter. If all checks out there, verify that
the following voltages are present at the output of the
auxiliary leads at the main transformer, T1.
CONTROL PC BOARD
AUXILIARY LEAD VOLTAGES
Main Transformer (T1)
Plug P8
Approximate
Auxiliary Lead Number
Locations
Voltage
209 to 210
1 to 9
18 VAC
201 to 204
4 to 6
18 VAC
231 to 232A
2 to 12
115 VAC
211A to 212
13 to 14
23 VAC
Often, replacement with a known good board is the
best service method. Remove the board that is sus-
pected to be defective. Carefully look over the board,
checking for burnt traces or components. If none are
found, install the known good board. If the trouble goes
away, reinstall the suspected bad board to confirm that
the board was indeed at fault. If the problem is now
gone with the original board installed, the problem is
probably with one of the leads or connectors going to
the board.
Consult the Lincoln Service Department if further trou-
bleshooting assistance is required.
