PINION-PLANETARY 0546549 - Caterpillar

The high voltage that is produced by an operating generator set can cause severe injury or death. Before performing any maintenance or repairs, ensure that the generator will not start.Place the engine control switch in the "OFF" position. Attach "DO NOT OPERATE" tags to all starting controls. Disconnect the batteries or disable the starting system. Lock out all switchgear and automatic transfer switches that are associated with the generator.
Illustration 1 g00992269
(1) Positive DC terminal or Negative DC terminal
(2) AC terminal
(3) AC terminal
(4) AC terminal The following procedure tests all three diodes within a block. Check the positive rectifier block and the negative rectifier block. If any meter reading does not fall within the given ranges, replace the rectifier block.
Set the digital multimeter on the diode range. Remove all leads from the rectifier block.
To test the negative rectifier block, follow these steps:
Place the red test lead on the negative "-" terminal (1). Place the black test lead on the following rectifier terminals: AC terminal (2), AC terminal (3) and AC terminal (4). All readings on the meter should be between 0.4 and 1.0.
Place the black test lead on the negative "-" terminal (1). Place the red test lead on the following rectifier terminals: AC terminal (2), AC terminal (3) and AC terminal (4). In all cases, the meter should read "OL" (overload).
To test the positive rectifier block, follow these steps:
Place the red test lead on the positive "+" rectifier terminal (1). Place the black test lead on the following rectifier terminals: AC terminal (2), AC terminal (3) and AC terminal (4). In all cases, the meter should read "OL" (overload).
Place the black test lead on the positive "+" rectifier terminal (1). Place the red test lead on the following rectifier terminals: AC terminal (2), AC terminal (3) and AC terminal (4). All readings on the meter should be between 0.4 and 1.0. Note: A shorted diode can damage the exciter rotor. If a diode is shorted, check the exciter rotor. Refer to the Testing and Adjusting, "Winding - Test" and Testing and Adjusting, "Insulation - Test". Perform these tests.