Lincoln Electric 11519 Service Manual page 72

F-26
ACTIVE SCR RECTIFIER ASSEMBLY TEST (continued)
9. Connect the tester to the SCR 1 as shown in
Figure F.8.
a. Connect tester lead (A) to the anode.
b. Connect tester lead (C) to the cathode.
c. Connect tester lead (G) to the gate.
10. Close switch SW-1.
NOTE: Switch SW-2 should be open.
11. Read meter for zero voltage.
a. If the voltage reading is higher than zero,
the SCR is shorted.
12. Close or keep closed switch SW-1.
13. Close switch SW-2 for 2 seconds and release
and read meter.
a. If the voltage is 3 to 6 volts while the switch
is closed and after the switch is open, the
SCR is functioning.
b. If the voltage is 3 to 6 volts only when the
switch is closed or there is no voltage
when the switch is closed, the SCR is
defective.
NOTE: Be sure battery is functioning properly. A
low battery can affect the results of the
test. Repeat Battery Test Procedure in
Step 6 if needed.
14. Open switch SW-1.
TROUBLESHOOTING AND REPAIR
Power MIG® 255XT
15. Reconnect the tester leads. See Figure F.8.
a. Connect tester lead (A) to the cathode.
b. Connect tester lead (C) to the anode.
c. Disconnect test lead (G) from the gate.
16. Close switch SW-1.
17. Read meter for zero voltage.
a. If the voltage is zero, the SCR is function-
ing.
b. If the voltage is higher than zero, the SCR
is shorted.
18. Perform the Active Test Procedure outlined in
Steps 6-15 for SCR 2.
19. Replace all SCR assemblies that do not pass
the above tests.
20. Reconnect plug J6 onto the control PC board
and J9 to the snubber PC board.
21. Reconnect leads X2 and X3 to the negative
capacitor bank bus bar.
22. Replace the tool tray and case sides.
F-26