Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 76

F-24
ARC START TRIGGER CIRCUIT TEST (continued)
PROCEDURE
1. Remove input power to the machine.
2. With the 5/16" nutdriver, remove the screws and
carefully lower the front control panel.
3. Locate plug J9 on the control PC board.
WARNING
ELECTRIC SHOCK can kill.
• With input power ON, there
are high voltages inside the
machine. Do not reach into
the machine or touch any
internal part of the machine
while power is on.
4. Turn on input power to the machine.
5. Close the Arc Start switch or jumper pins "D" to
"E" at the 6-pin amphenol receptacle.
Figure F.2.
6. With the volt/ohmmeter, check for 24 VAC at
pins 1J9 to 3J9.
TROUBLESHOOTING AND REPAIR
FIGURE F.2 – 6-PIN AMPHENOL RECEPTACLE
A
B
See
SQUARE WAVE TIG 355
F
E
D
C
• If 24 VAC is present, the control PC board may
be faulty.
NOTE: 24 VAC should be present at pins 1J9 to
3J9 only when the Arc Start switch is
closed.
• If 24 VAC is missing or low, check for 24 VAC at
the T5 transformer. See the Wiring Diagram. If
24 VAC is missing or low at the transformer
leads, perform the Control Transformer Test.
• If 24 VAC is present at the transformer leads,
remove input power to the machine and check
the continuity and resistance of the leads and
coils on and between the feed-thru board and
the protection board. See Figure F.3.
7. Also check the continuity of the leads from the
protection board to the 14-pin amphenol recep-
tacle. It should be zero ohms. See the Wiring
Diagram.
8. After the tests are complete, install the front
control panel, using the 5/16" nutdriver.
F-24