Alternator: Testing and Inspection

1. INSPECT ROTOR FOR OPEN CIRCUIT
Using an ohmmeter, check that there is continuity between the slip rings.

Standard resistance: 2.1 - 2.5 Ohms at 20 °C (68 °F)

If there is no continuity, replace the rotor.

2. INSPECT ROTOR FOR GROUND
Using an ohmmeter, check that there is no continuity between the slip ring and rotor.
If there is continuity, replace the rotor.

3. INSPECT SLIP RINGS
a. Check that the slip rings are not rough or scored.
If rough or scored, replace the rotor.
b. Using vernier calipers, measure the slip ring diameters.

Diameter:

If the diameter is less than minimum, replace the rotor.

4. INSPECT STATOR FOR OPEN CIRCUIT
Using an ohmmeter, check that there is continuity between the coil leads.
If there is no continuity, replace the drive end frame assembly.

5. INSPECT STATOR FOR GROUND
Using an ohmmeter, check that there is no continuity between the coil leads and drive end frame.
If there is continuity, replace the drive end frame assembly.

6. INSPECT EXPOSED BRUSH LENGTH
Using vernier calipers, measure the exposed brush length.

Exposed length:

If the exposed length is less than minimum, replace the brushes (70 A type) or brush holder assembly (100 A type).

7. INSPECT POSITIVE RECTIFIER

a. Using an ohmmeter, connect one tester probe to the positive (+) terminal and the other to each rectifier terminal.
b. Reverse the polarity of the tester probes and repeat step (a).
c. Check that one shows continuity and the other shows no continuity.
If continuity is not as specified, replace the rectifier holder.

8. INSPECT NEGATIVE RECTIFIER

a. Using an ohmmeter, connect one tester probe to each negative (-) terminal and the other to each rectifier terminal.
b. Reverse the polarity of the tester probes and repeat step (a).
c. Check that one shows continuity and the other shows no continuity.
If continuity is not as specified, replace the rectifier holder.

9. INSPECT BEARING
Check that the bearing is not rough or worn.
If necessary, replace the bearing.