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6.4.6 Technician Troubleshooting Guides
TROUBLESHOOTING THE 24VAC POWER SUPPLY SYSTEM
Is 24VAC
present on the load side of
the transformer?
Transformer has
failed. Replace.
24VAC Power Supply
System is OK.
Causes are broken or loose wiring
or a failed contactor. If wiring and
connections are verified to be intact,
replace contactor.
Place the master ON/
OFF switch in the ON
position.
Was there an
audible snap from the
contactor indicating the
coil energized?
Yes
Is 24VAC present
across Pins 1and 2
of the 15-pin connector
on the front of the
contactor box?
No
No
Yes
Yes
Verify continuity of
master ON/OFF switch in ON position.
Replace switch as required.
If switch is OK, causes are broken
or loose wiring. Check connections and
replace wiring as required.
Yes
The primary indicator of a
problem with the 24VAC
Power Supply System is a
failure of the computer to
activate when the master
ON/OFF switch is placed
in the ON position and the
computer ON/OFF switch
is pressed.
Verify that the power cord is
properly connected to the
electrical service and that
the circuit breaker is not
tripped.
Is line voltage
present on the line side of
the transformer?
No
Check 5-amp transformer
fuse. Replace if blown. If fuse
is OK, cause is loose or broken
wiring, or the electrical service
circuit is dead.
No