Stator: Testing and Inspection

Fig. 13 Testing diode trio:

Fig. 14 Alternator w/integral regulator rectifier short or grounded & stator grounded test:

RECTIFIER SHORT OR GROUNDED & STATOR GROUNDED TEST
Using a suitable ohmmeter, connect one probe to the alternator BAT terminal, Figs. 13 and 14, and the other probe to the STA terminal (rear blade terminal). Then, reverse the ohmmeter probes and repeat the test. A reading of about 6.5 ohms should be obtained in one direction and no needle movement with the probes reversed. A reading in both directions indicates a bad positive diode, a grounded positive diode plate or a grounded BAT terminal.
Perform the same test using the STA and GND (ground) terminals of the alternator. A reading in both directions indicates either a bad negative diode, a grounded stator winding, a grounded stator terminal, a grounded positive diode plate, or a grounded BAT terminal.
Infinite readings (no needle movement) in all four probe positions in the preceding tests indicates an open STA terminal lead connection inside the alternator.

Fig. 15 Testing rectifier bridge diodes:

FIELD OPEN OR SHORT CIRCUIT TEST
Exc. Alternators W/Integral Regulators
Using a suitable ohmmeter, connect the alternator field terminal with one probe and the ground terminal with the other probe, Fig. 15. Then, spin the alternator pulley. The ohmmeter reading should be between 2.4 and 25 ohms on 1980 units, 2.4 and 100 ohms on all 1981-85 units and 1986-87 models less IAR system, and should fluctuate while the pulley is turning. An infinite reading (no meter movement) indicates an open brush lead, worn or stuck brushes, or a bad rotor assembly. An ohmmeter reading of less than 2.4 ohms indicates a grounded brush assembly, a grounded field terminal or a bad rotor.

Fig. 16 Alternator w/integral regulator field open or short circuit test:

Alternators W/Integral Regulators
1. Using a suitable ohmmeter, connect regulator A blade terminal with one probe and the regulator ``F'' screw head with the other probe, Fig. 16.
2. Spin the alternator pulley and note meter reading, then reverse probes and repeat step 1. In one probe direction ohmmeter reading should be between 2.2 and 100 ohms and may fluctuate while pulley is turning. In the other direction, reading should fluctuate between 2.2 and approximately 9 ohms.
3. An infinite reading (no meter movement) in one direction and approximately 9 ohms in the other, indicates an open brush lead, worn or stuck brushes, defective rotor or a loose regulator to brush holder attaching screw.
4. An ohmmeter reading less than 2.2 ohms in both directions indicates a shorted or defective regulator.
5. An ohmmeter reading significantly over 9 ohms in both directions indicates a defective regulator or loose ``F'' terminal screw.
6. Connect alternator rear housing with one ohmmeter probe and touch the other probe to the regulator ``F'' terminal. Reverse probes and repeat test. Ohmmeter reading should be infinite in one probe direction and approximately 9 ohms in the other.
7. If ohmmeter reads less than infinite at either point, a grounded brush lead, grounded rotor or defective regulator is indicated.