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 18
Trouble, Symptom,
Condition. Probable Cause. Test, Check, and/or Remedy.
Generator.
1. No (or low) voltage output
. a. Shorted diode in exciter
rectifier (CR2).
Check diodes in accordance with Section
2-3. If diodes are good, proceed to step B.
b. Open or shorted exciter
rotor winding (G2). Use ohmmeter to check for open or
shorted condition diodes in accordance
with Section 2-3. If exciter rotor windings
are good, proceed to step C.
c. Open or shorted exciter field
windings (L2).
Check field resistance. See Section 2-3
for normal values.
d. Open or shorted generator
rotor windings (L1). Check resistance with ohmmeter to
determine if open or short circuited diodes
in accordance with Section 2-3
2. Generator operates
single phase. a. Open or short circuited
winding in generator stator
(G1).
Check stator-winding resistances. See
Section 2-3 for normal values.
3. Generator overheats. a. Loose connection causing
high resistance.
Check all output connections. Look for
discoloration caused by heat. Tighten or
replace as required.
b. Improper or blocked
ventilation. Check for foreign material (rags, etc.)
blocking airflow. Provide adequate
ventilation.
c. Generator stator windings
short circuited.
Check stator windings. See Section 2-3.
4. Unbalanced output a. Loose connection in output
circuit.
Check all output connections. Discolored
connectors indicate a loose connection.
Tighten or replace as required.
b. Open or short circuited
phase. Check stator windings in accordance with
Section 2-3. Repair or replace as required.
c. Defective connection in
output circuit.
Check plug and receptacle connectors at
aircraft. Tighten, repair, or replace as
required.
b. Break or cut in output cable
assembly. Inspect. Repair or replace as required.
c. Unbalanced load. Check aircraft 400-Hz components.