Hobart 120CU20, Operation And Maintenance Manual With Illustrated Parts List

Page: 118 / 246

OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
October 15, 2013 Chapter 2-4
Page 20
Trouble, Symptom, Condition Probable Cause Test, Check, and/or Remedy
T-R Controls and Components (continued)
2. (continued) e. Interlock signal not being
received from the aircraft.
Be sure the output cable is
properly inserted into the aircraft
receptacle and try again.
Verify 28 VDC is on the DC+
connection of the GPU and/or
being sent from the aircraft.
If aircraft is sending signal but not
being received at the GPU DC+
and the cable is properly inserted
into the aircraft receptacle, verify
the K403 relay is operating.
If K403 relay is operating, replace
output cable.
If all the above appears to be
working, replace the TRB board.
3. “STARTING CURRENT ” push-
button sets the current limit, but
the system is not current limiting.
a. Defective push-button switch. At rated speed, measure the
voltage across the switch. The
voltage should read approximately
5 VDC. Press the switch again
and the voltage should go to 0 V.
If voltage does not go to 0 V, the
switch is defective and needs to
be replaced.
b. Defective TRB PC Board. Replace TRB PC board with a
board known to be operating
properly. If current limiting is still
not operating, contact the factory.
4. “STARTING CURRENT ” push-
button does not increment the
current limiting values.
a. Defective push-button switch. At rated speed, measure the
voltage across the switch. The
voltage should read approximately
5 VDC. Press the switch again
and the voltage should go to 0 V.
If voltage does not go to 0 V, the
switch is defective and needs to
be replaced.
b. Defective TRB PC Board. Replace TRB PC board with a
board known to be operating
properly. If contactor still doesn’t
close, contact the factory.