Lang GCCO-T Service Manual page 45

PROBABLE CAUSE
Defective control transformer
(12 VAC).
Defective rectifier
Note: Display should now be operating.
TROUBLESHOOTING GCCO-C CONT'D
CORRECTIVE ACTION
Check transformer for normal operation.
Check primary coil for 120 VAC and 154.1 Ω. Check secondary coil
for no less than 10.5 VAC and 1 Ω.
If voltage is measured on primary:
Check for voltage on secondary.
Replace transformer.
If voltage is not measured on primary:
Check wires for any shorts.
Check for no less than 10.5 VAC on TP1 and 5 VDC on TP2.
If correct voltage is present at TP1 and present, but low at TP2
unplug both ribbon connections from CPU and re-measure at TP2.
If voltage remains low at TP2 replace CPU (40102-311).
If voltage at TP2 increased to 5 VDC when ribbon was unplugged,
plug ribbon back in to CPU and disconnect from Interface board.
Re-measure at TP2.
If voltage dropped to below 5 VDC replace ribbon cable (31110-01).
If voltage remains at 5 VDC, plug ribbon back into Interface board
and measure for 5 VDC at TP3.
If voltage is present at TP3 and display is still not on, press and hold
the R/C button on board if LED's come on replace Interface board.
If LED segment does not illuminate or the LED is blank, replace
LED.
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