Piper Arrow IV Turbo Maintenance Manual page 219

2. 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.
3. 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 stator
lead, and the other test bulb or ohmmeter probe to the stator frame. If the test bulb lights, or the 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.
4. Bearings and Seals: Whenever the alternator is overhauled, new bearings and oil or grease seals are
recommended, even though the bearings and seals appear to be in good condition. A faulty seal can cause an
alternator to fail within a very short period of time.
ASSEMBLY OF ALTERNATOR.
1. Press the ball bearing into the drive end head using a flat block approximately two inch square so that
the pressure is exerted on the outer race of the bearing. Install the retainer plate. With the snap ring and retainer
cup in place on the rotor shaft, use a tool that fits over the shaft and against the inner bearing race, and press
until the inner bearing race is against the snap ring retainer cup. (Refer to Figure 24-35.)
2. Carefully install the rectifiers in the slip ring end head or rectifier mounting plate by supporting the
unit and using the special tools illustrated in Figure 24-36.
Use an arbor press, do not hammer. Reconnect the stator leads to
the rectifiers. When soldering these connections, use pliers as a
heat dam on the lead between the solder point and the rectifier.
Too much heat will damage the rectifiers.
3. Reassemble the rectifier mounting plate studs and insulators, making sure they are in the correct order.
(Refer to Figure 24-37.)
4. After the slip ring end head is completely assembled, the stator and rectifier leads must be secured to
the rectifier mounting plate with epoxy. Make sure the stator leads are positioned so that they do not interfere
with the rotor.
EFFECTIVITY:
PRESTOLITE ALTERNATOR
PIPER AIRCRAFT
PA-28RT-201 / 201T
MAINTENANCE MANUAL
—CAUTION—
1J3
24-33-07
Page 24-32
Revised: July 13, 1983