d. Remove the nuts, lock washers, flat washers and insulators from the output and auxiliary terminal studs.
Note carefully the correct assembly of the insulator washers and bushing. Using the special tools shown in
Figure 11-5, support the end head and press out the three rectifiers. The end head can now be separated from the
stator assembly.
e. To remove the slip ring end bearing and grease seal, it will be necessary to have a hook type or impact type
bearing puller as shown in Figure 11-6. Do not remove the bearing unless replacement is necessary.
—NOTE—
The inner race of the slip ring end bearing is pressed onto the rotor
shaft. When bearing replacement is necessary, always replace the
complete bearing assembly including the inner race.
f. To remove the drive end head from the rotor shaft, use a puller that grips on the bearing retainer plate as
shown in Figure 11-7. Do not attempt to remove by supporting the end head and pressing on the shaft, as this
may result in distortion of the end head or stripping of the retainer plate screws. Remove the three retainer plate
screws and press the bearing out of the end head. (Refer to Figure 11-7.)
11-11. INSPECTION AND TESTING OF COMPONENTS. Upon completion of 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 11-8). 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 11-9, or use an
ohmmeter. Rotor current draw and resistance are listed in Paragraph 11-16 and Table XI-II. 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 defect he
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.
c. Stator: The stator can be tested for open or grounded windings with a 12 volt test bulb, described in the
rectifier section, or an ohmmeter in the following manner. Separate the stator from the slip ring end head just far
enough to insert a fold of rags or blocks of wood. In other words, insulate the stator from the end head. To test
for grounded windings, touch one test bulb or ohmmeter probe to the auxiliary terminal or any other stator lead,
and the other test bulb or ohmmeter probe to the stator frame. If the test bulb lights, or ohmmeter indicates
continuity, the stator is grounded. To test for open windings, connect one test probe to the auxiliary terminal or
the stator winding center connection and touch each of the three stator leads. The test bulb must light, or the
ohmmeter must show continuity. Due to the low resistance in the stator windings, shorted windings are almost
impossible to locate. However, shorted stator windings will usually cause the alternator to "growl" or be noisy
during operation and will usually show some signs of overheating. If all other electrical checks are normal and
alternator fails to supply its rated output, the stator should be replaced to determine whether or not it is the faulty
component.
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
ELECTRICAL SYSTEM
2D2