5-66. APU GENERATOR-Continued
Testing of Generator consists of continuity checks using wiring
diagram (Appendix F).
Most of the following tests can be performed without
disassembling the generator. Clearly mark all leads dis-
connected, together with the point taken from.
(1) Armature. Remove all brushes from their holders.
(2) Using ohmmeter, check for continuity in the ac winding for an open circuit between the slip rings. If
an open circuit is found, replace the armature.
(3) Test both the slip rings and commutator for short or grounding to he shaft.
(4) To test the armature for an open circuit in the dc windings 'O" reading indicates open circuit. Check
continuity between all adjacent bars of the commutator. Visually inspect for bar burring, arcing and
(5) Touch the probes to two adjacent bars and check for continuity. Move each probe over one bar and
check again. Continue around the commutator. Any adjacent bars that don't show continuity
indicate an open armature winding.
(6) This test can only be performed with the g nerator disassembled and requires a growler. To test for
shorts in the dc winding, place the armature in the growler. Operate the growler and pass a steel
strip back and forth over and above the armature windings. If the strip is magnetically attracted to
the armature at any point, a short is indicated. After testing in one position, rotate the armature
slightly and repeat the test. Do this for one complete revolution.
(7) If the test indicates a short circuit in the
dc windings, be sure the commutator is
Carbon dust, dirt or grease
between the bars or slip rings can cause
(8) If the tests show that the armature is
defective, replace it.
Field Winding Tests: The following
tests can be performed without
disassembling the generator, but the
field coil leads must all be
disconnected from their terminal points;
brush rig, control box, and external
connections. If a defective coil is
found, disassemble the generator and
replace the defective coil.
(10) With an ohmmeter or continuity lamp, check for grounding to the generator frame. Touch one prod
to the coil terminals and the other to a clean, paint-free part of the frame. If grounding is indicated,
separate the windings and check each one.