Checking Rotor; Slip Ring End Frame - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
(CHECK FOR GROUNDS)
C452
C452 BRUSH HOLDER
OHMMETER
ASSEMBLY
HEAT
SINK
DIODES
LEAD ATTACHING NUTS
OHMMETER (CHECK FOR SHORTS AND OPENS)
Figure 11-5. Checking Rotor
Figure 11-6. Slip Ring End Frame
ground which may have existed between stator windings
and either end frame
before disassembly.
Visually inspect very carefully for this possibility.
DIODE CHECKS: Each diode may be checked electrically for a shorted or open
condition.
Any one of the following methods may be used.
Ohmmeter
Method:
One method of checking diodes is to use an ordinary ohm-
meter.
The lowest range scale on the ohmmeter should be used, and the ohm-
meter
should have a 1-1/2-volt cell. To determine the cell voltage, turn the
selector to the lowest scale,
and then connect the ohmmeter leads to a volt-
meter. The voltmeter
will indicate the cell voltage.
With the stator disconnected,
check a diode in the heat sink by connecting
one of the ohmmeter leads to the heat sink, and the other ohmmeter
lead to the
diode lead, and note the reading. (Refer to Figure
11-8.) Then reverse the
ohmmeter lead connections, and note the reading.
If both readings are very low,
or if both readings
are very high, the diode is defective. A good diode will give
one low reading and one high reading.
Check the other two diodes in the heat
sink in the same manner.
To check a diode mounted in the end frame, connect one of the ohmmeter
leads to the end frame, and the other ohmmeter
lead to the diode lead (Refer to
Figure 11-7), and note the reading.
Then reverse the ohmmeter lead connec-
tions, and note the reading. If both readings
are very low, or if both readings
are very high, the diode is defective.
A good diode will give one low reading and
one high reading. Check the other two diodes in the endframe in the same manner.
Test Lamp Method: An alternate
method of checking the diodes is to use a test
lamp of not more than 28-volts in place of the ohmmeter.
Reissued: 10/12/79 ELECTRICAL SYSTEM
Effectivity
DELCO AR3