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

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OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
October 15, 2013 Chapter 2-4
Page 14
Trouble, Symptom, Condition. Probable Cause. Test, Check, and/or Remedy.
Load Contactor Operating Circuits.
Output 1: Contactor K1, Push-button switch S75.
Output 2: Contactor K201, Push-button switch S275.
1. Load contactor will not close
when the corresponding
Output push-button switch is
held in closed position.
Generator is running at normal
voltage. a. Blown contactor fuse (F3) on
regulator board.
Check the fuse and replace if
blown. If it blows again, check the
contactor.
b. In addition to defective wiring
and connections in AC and DC
load contactor actuating circuits,
load contactor may be
prevented from closing for any
one of following reasons:
Check all wiring and connections
in load contactor circuits.
c. Defective REG board. After making certain that the
output push-button switch is
working, measure the DC output
voltage at contactor coil. If the
voltage measured isn’t
approximately 90 VDC, replace
REG.
Replace REG board with a board
known to be operating properly. If
contactor still doesn’t close,
proceed to step
d .
d. Defective Output 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.
e. Defective coil in load contactor. Disconnect leads at load contactor
terminals V and W. Check coil
resistance between these
terminals. Resistance should be
approximately 600 ohms. If coil is
defective, replace complete load
contactor.