SCREW 3F0952 - Caterpillar

Testing A Brushless Exciter Rotating Rectifier With An Ohmmeter
Table 1
Tools Needed
Part Number Part Name Quantity
237-5130 Digital Multimeter 1
257-9140 Multimeter 1
146-4080 Digital Multimeter (RS-232) 1
7X-1710 Multimeter Probe Group 1
Illustration 1 g00555106 If the failure of a rectifier is suspected, use the following procedure.
Remove the cover from the exciter.
Remove the nut that secures the rectifier to the heat sink.
Remove the diode lead.
Lift the rectifier from the heat sink.
Refer to Illustration 1. Connect the ohmmeter's leads across the rectifier. Note the meter reading.
Reverse the ohmmeter leads. Note the meter reading. The ohmmeter should indicate a low resistance when the ohmmeter leads are across the rectifier in one direction. The ohmmeter should indicate a high resistance when the leads are reversed.If the ohmmeter indicates a low resistance in both directions, the rectifier is shorted. A high resistance in both directions indicates an open rectifier.Replace any faulty rectifiers with rectifiers that have comparable operating characteristics. Include the following information when a rectifier is being ordered for replacement:
Part Number of the rectifier
Model number of the exciter
Type of the exciter
Serial number of the generatorTesting a Brushless Exciter Rotating Rectifier With A Test Light
Illustration 2 g00555113
Test Light
If an ohmmeter is not available, a rectifier can be tested by using a test light. A test light consists of two standard flashlight batteries and a flashlight bulb. Refer to Illustration 2. If the failure of a rectifier is suspected, use the following procedure.
Remove the cover from the exciter.
Remove the nut that secures the rectifier to the heat sink.
Remove the diode lead.
Lift the rectifier from the heat sink.
Connect the leads of the test light across the rectifier. Notice if the bulb is illuminated.
Reverse the leads of the test light across the rectifier. Notice if the bulb is illuminated. The bulb should be illuminated when the leads of the test light are across the rectifier in one direction. The bulb should not be illuminated when the leads are reversed.If the bulb is illuminated in both directions, the rectifier is shorted. If the bulb is not illuminated in either direction, the rectifier is open.Replace any faulty rectifiers with rectifiers that have comparable operating characteristics. Include the following information when a rectifier is being ordered for replacement:
Part Number of the rectifier
Model number of the exciter
Type of the exciter
Serial number of the generator