TP-6391 9/08 49Section 5 Component Testing and Adjustment
5. Check the rotor for continuity and resistance.
Raise the brushes from the slip rings while
performing ohmmeter tests. Measure the rotor
resistance (ohms) between the two slip rings; see
Figure 5-7. See Section 1.4, Alternator
Specifications, for rotor resistance readings. If the
resistance readings are low, perform a
megohmmeter test on rotor as described in the
next step.
Note: Because ohmmeter accuracy varies,
resistance readings are approximate. Take
readings at room temperature.
2-221
R13929-7
Figure 5-7 Rotor Resistance Check
6. Perform a megohmmeter test to determine
whether the rotor is shorted to ground.
a. Raise and secure the brushes away from the
slip rings by inserting a retaining wire in the
brush holder hole.
b. Using a megohmmeter, apply 500 volts DC to
one rotor slip ring and the rotor poles or shaft.
Follow the instructions of the megohmmeter
manufacturer when performing this test.
Note: A reading of approximately 500 kOhms
(1/2 megohm) or higher indicates a
good rotor.
c. Repair or replace the rotor if the reading is less
than approximately 500 kOhms. A reading of
less than 500 kOhms indicates deterioration of
the winding insulation and possible current flow
to ground.
d. Following the test, remove the retainer wire
from the brush holder and check the brush
positions on the slip rings. See Section 5.6,
Brushes.
e. Reinstall the brush cover on the end bracket.
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