Service manual

troubleshooting trees
T r o u b l e s h o o T i n g T r e e s • C o m b i t h e r m C t e x p r e s s t e C h n i C a l s e r v i C e m a n u a l • D – 22
No Display/No Operation - Simple Control
Is voltage across L1/L2 at
main TB?
Is voltage across terminal
1/F1 and terminal 1/F2
6.3A fuses?
Is voltage across terminal 2/F1
and terminal 2/F2 6.3A fuses?
Check cord/plug/main
circuit breaker – Install/
Repair/Reset as needed
No
Yes
Yes
No
Repair wiring between main TB
and F1/F2 fuses
No
Yes
No replace blown F1/F2
fuses(s)
Repair wiring between F1/F2
and power supply
Is voltage across L1/N at
power supply?
No
Is 12 VDC across terminals V+
and V- at power supply?
Replace power supply
Is the ribbon cable securely
seated at the RBL and the
display board?
Correct cable and retest
Is 12 VDC across RBL
terminals X8-pins 1-2?
Repair wiring between power
supply and RBL
Is there continuity across
all ribbon cable connection
points end-to-end?
No
Yes
Yes
No
No
Yes
Yes
Replace ribbon cable
No
Yes
Is there 12 VDC at pins
31/32 and 33/34 on the
ribbon cable?
Replace relay board
No
Yes
Is there 12 VDC across pin
1-2 on On/Off board?
Test On/Off board cable
for continuity. If cable ok,
replace display board
No
Yes
Test On/Off board -
On = Temporary switch between 1-3
Off = temporary switch between 1-4
Replace On/Off board as needed, if On/Off
board tests ok, replace display board