Piper COMANCHE PA-24-180 Service Manual page 540

the armature core). The steel strip will vibrate above the area of the armature core in which short circuit
armature coils are located. If the short circuit is obvious. it can often be repaired so that the armature can be
saved.
9-1 1. Unsteady Or Low Output. If the generator produces a low or unsteady output. the following factors
should be considered
a. A loose drive belt will slip and cause a low or unsteady output.
b. Brushes which stick in their holders, or low brush spring tension will prevent good contact between
the bl ashes and commutator so that output will be low and unsteady. This will also cause arcing and burning
of the brushes and commutator.
c.
If the commutator is dirty, out of round. or has high mica. generator output is apt to be low and
unsteady. The remedy here is to turn the commutator down in a lathe and undercut the mica. Burned
commutator bars may indicate an open circuit condition in the armature as already stated above. (Refer to
Paragraph 9-10 )
9-12 Excessive Output.
a.
When a generator produces excessive output on an application. the procedure for determining
whether the trouble is in the generator. regulator. or elsewhere is outlined in Paragraph 9-5. If the generator
output remains high. even with the "F" terminal lead disconnected, then the trouble is in the generator itself.
and it must be further analyzed to locate the source of trouble.
b.
In the system which has the generator field circuit grounded externally. accidental internal
grounding of the field circuit would prevent normal regulation so that excessive output might be produced
by the generator. On this type of unit. an internally grounded field which would cause excessive output ma\
be located by use of test points connected between the "F" terminal and the generator frame. Leads should
disconnected from the "F" terminal and the brush to which the field lead is connected inside the generat
should be raised from the commutator before this test is made. If the lamp lights. the field is internal
grounded If the field has become grounded because the insulation on a field lead has worn away. repair can be
made by reinsulating the lead. It is also possible to make repair where the ground has occurred at the pole shoes
by removing the field coils and reinsulating and reinstalling them. A ground at the "F" terminal stud can be
repaired by installing new insulating washers or bushings.
NOTE
If battery temperature is excessive. battery overcharge is apt to
occur, even though regulator settings are normal. Under this condi-
tion. it is permissible to reduce the voltage regulator setting as
explained in the applicable bulletin pertaining to the regulator used
on the application.
9-13 Noisy Generator. Noise emanating from a generator may be caused bya loose mounting. drive pulley.
or gear: worn or dirty bearings: or improperly seated brushes. Dirty bearings may sometimes be saved by
cleaning and relubrication. but worn bearings should be re-laced Brushes can be seated as explained in
Paragraph 9-7 If the brush holder is bent. it may be difficult to reseat the brush so that it will function
properly without excessive noise. Such a brush holder will require replacement.
ISSUED: 8/18/72
ELECTRICAL SYSTE
PIPER COMANCHE SERVICE MANUAL
3A15