Lang GCCO-T Service Manual page 51

NO DISPLAY
PROBABLE CAUSE
Defective Power Switch (-PP
only)
Defective Power Switch
output on circuit board
(JP37)
Defective Control
Transformer
Defective Display
TROUBLESHOOTING GCCO-PP / -PT CONT'D
CORRECTIVE ACTION
Confirm that toggle switch is getting correct voltage.
Check power switch for normal operation.
Confirm that JP37 has 5VDC in the off position and nominal voltage
in the on position.
If JP37 has a constant 5VDC check toggle switch for normal
operation.
Confirm that 208/240VAC is feeding primary coil.
Confirm that 24VAC and 12VAC is at JP40 (24VAC across solid
yellow wires and 12VAC from one solid yellow wire to yellow with
red stripe).
Check ribbon cable connections.
Confirm that voltage is present at JP40.
If no voltage is present:
Replace control transformer.
If voltage is present:
Confirm that CPU has 5VDC at TP1 (this means that the CPU is
getting correct voltage).
Confirm that CPU has 12VDC at TP2 (this means that the CPU is
sending out the correct voltage).
If no voltage is present:
Replace CPU.
If voltage is present:
Replace display.
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