Piper Navajo PA-31 Service Manual page 723

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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 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.
d. 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.
PIPER NAVAJO SERVICE MANUAL
367
Figure
11-24. Installation
of
Bearing
Figure
11-25. Installation
of
Rectifier
Reissued: 10/12/79
Effectivity
PRESTOLITE
ELECTRICAL SYSTEM
4B21