Alternator: Testing and Inspection

ROTOR




1. Check the rotor coil for continuity. Check to make sure that there is continuity between the slip rings. If resistance is extremely low, it means that there is a short. If there is no continuity or if there is a short circuit, replace the rotor assembly.

Resistance value : Approx. 3.1 ohms




2. Check the rotor coil for ground. Check to make sure that there is no continuity between the slip ring and the core.
If there is continuity, replace the rotor assembly.

STATOR




1. Make a continuity check on the stator coil. Check to make sure that there is continuity between the coil leads.
If there is no continuity, replace the stator assembly.




2. Check the coil for grounding. Check to make sure that there is no continuity between the coil and the core.
If there is continuity, replace the stator assembly.

RECTIFIERS




POSITIVE RECTIFIER TEST
Check for continuity between the positive rectifier and stator coil lead connection terminal with an ohmmeter. The ohmmeter should read continuity in only one direction. If there is continuity in both directions, a diode is shorted.
Replace the rectifier assembly.




NEGATIVE RECTIFIER TEST
Check for continuity between the negative rectifier and the stator coil lead connection terminal. The ohmmeter should read continuity in only one direction. If there is continuity in both directions, a diode is shorted, and the rectifier assembly must be replaced.




DIODE TRIO TEST
Check the three diodes for continuity by connecting an ohmmeter to both ends of each diode. Each diode should have continuity in only one direction.

If continuity is present in both directions, a diode is defective and the heatsink assembly must be replaced.




BRUSH REPLACEMENT
Replace the brushes if they are worn to the limit line.




1. de-solder the pigtail and remove the old brush and spring.
2. Install the brush spring and a new brush in the brush holder.
3. Insert the brush so that there is a space of 2 to 3 mm (0.079 to 0.118 in.) between the limit line and the end of the brush holder.




4. Solder the pigtail to the brush holder.