Lincoln Electric SVM175-A WELD CONTROL FEEDBACK TEST (continued)

TROUBLESHOOTING & REPAIR
F-73 F-73
RANGER 305D
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WELD CONTROL FEEDBACK TEST (continued)
16. If the voltage readings are different, check
the wiring and connections between the
welding terminals and the control PC board.
See the wiring diagram.
17. Connect the millivolt meter probes between
lead #206S+ (P6-2) and lead 204S- (P6-1).
See Wiring Diagram. If the machine is cur-
rently producing 200 amps the millivolt
meter should read about 25 millivolts.
18. If the machine cannot produce 200 amps of
weld current, the correct millivolt signal will
need to be calculated by dividing the read-
ing displayed on the external ammeter by 8.
See the following explanation.
19. The shunt used in this machine will produce
50 millivolts at a load of 400 amps, or 8
amps per millivolt.
20. To calculate the correct millivolt signal for a
given load, you divide the number of amps
displayed on the ammeter by 8.
Example: If your ammeter reads 75, (75/8 =
9.4) If the shunt is working correctly,and th
wiring between the shunt and the control PC
board is in good condition, the meter con-
nected at the control PC board should be
reading about 9.4 millivolts.
21. If the millivolt reading is incorrect, check the
wiring between the shunt and the control PC
board for damage, grounds, and faulty con-
nections. If the wiring is good, the shunt
and lead assembly is faulty and should be
replaced.
22. Perform the Case Cover Replacement
Procedure.