Lincoln Electric SQUARE WAVE TIG 255 SVM100-A Service Manual page 65

TROUBLESHOOTING & REPAIR
ARC START TRIGGER CIRCUIT TEST (continued)
CONTROL BOX
CONTROL BOARD LOCATED INSIDE
PROTECTION/SNUBBER BOARD
LOCATED ON BACK OF CONTROL BOX
FIGURE F.7 - LOCATION OF PROTECTION/SNUBBER BOARD.
TEST PROCEDURE
1. Remove main supply power to machine
2. Remove plug J6 from the control 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.
J2
J3
J1
G2150
SQUARE WAVE 255 CONTROL
FIGURE F.8 - CONTROL BOARD TEST POINTS.
SUPORT CASE BACK
AND CENTER BAFFLE
WITH WOOD 2 X 4
Note: If arc start switch is opened or
jumper removed from pins "D" and "E"
the measured resistance in Step 4
should be infinite.
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.
A. If zero ohms resistance is indicated,
B. If a resistance of any value is
PLUG J6 REMOVED
J4 J5 J7
J6
J8
test is okay. Go to Step 6.
shown, check wires and connec-
tions.
10J6
3J6
SQUARE WAVE TIG 255
F-24