Testing Rotor For Shorts - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
3658
365A
RHEOSTAT
Figure 11-22.
Testing Rotor
For Ground
Figure 11-23.
Testing Rotor
For Shorts
11-31. INSPECTION AND TESTING OF COMPONENTS.
Upon completion of the
disassembly, all parts should be cleaned and visually inspected
for cracks, wear, or distortion
and any signs of overheating or mechanical interference.
a. Rotor: The rotor should be tested for grounded or shorted
windings. The ground
test can be made with test probes, connected in series
with a 110-volt test lamp, an
ohmmeter or any type of continuity tester. (Refer to Figure
11-2.) There must not be any
continuity between the slip rings and the rotor shaft or poles.
To test for shorted turns in
the rotor winding, connect a voltmeter, ammeter and rheostat
as shown in Figure I 1-23. or
use an ohmmeter. Rotor current draw and resistance are listed
in the Alternator Service Test
Specifications paragraph. Excessive current draw or a
low ohmmeter reading indicates
shorted windings. No current draw or an infinite ohmmeter
reading would indicate an open
winding.
b. Rectifiers: A diode rectifier tester will detect and
pinpoint open or shorted
rectifiers without going through the operation of disconnecting
the stator leads. However, if
a tester is not available, test probes and a No. 57 bulb, connected
in series with a 12-volt
battery, can be used in the following manner. Touch one
test probe to a rectifier heat sink
and the other test probe to a lead from one of the rectifiers
in that heat sink. Then reverse
the position of the leads. The test bulb should light in one
direction and not light in the
other direction. If the test bulb lights in both directions, one
or more of the rectifiers in that
heat sink is shorted. To pinpoint
the defective rectifier, the stator leads must be
disconnected and the above test repeated on each rectifier.
Open rectifiers can only be
detected, when using the test bulb, by disconnecting the stator
leads. The test bulb will fail
to light in either direction if the rectifier is open.
Reissued: 10/12/79
Effectivity
PRESTOLITE
4B20
ELECTRICAL
SYSTEM