Bench Tests

Fig. 14 Side terminal alternator rectifier short or grounded & stator grounded test:

Fig. 15 Rear terminal alternator rectifier short or grounded & stator grounded test:

Fig. 16 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 or B+ terminal, Figs. 14, 15 and 16, the other probe to the STA terminal (rear blade terminal). Then, reverse the ohmmeter probes and repeat the test. A reading of about 6---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, grounded BAT or B+ terminal or a shorted radio suppression capacitor, if equipped. 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 shorted radio capacitor, if equipped. Infinite readings (no needle movement) in all four probe positions in the proceeding tests indicates an open terminal lead connection inside the alternator.

Fig. 17 Side terminal alternator field open or short circuit test:

Fig. 18 Rear terminal alternator field open or short circuit test:

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, Figs. 17 and 18. Then, spin the alternator pulley. The ohmmeter reading should be 2.4 and 100 ohms, 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 less than 2.4 ohms indicates a grounded brush assembly, a grounded field terminal or a bad rotor.

Fig. 19 Alternator w/integral regulator field open or short circuit test:

Regulators W/Integral Regulator
1. Using a suitable ohmmeter, connect regulator A blade terminal with one probe and the regulator ``F'' screw head with the other probe, Fig. 19.
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 first to regulator ``A'' blade terminal and then to the regulator ``F'' screw head.
7. If ohmmeter reads less than infinite at either point, a grounded brush lead, grounded rotor or defective regulator is indicated.