PMG3516 Power Module Caterpillar

Three-Diode Rectifier Block

Illustration 1	g00610240

Illustration 2	g00613971
Three-Diode Rectifier Block (two pieces)

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.

1. Set the digital multimeter on the diode range. Remove all leads from the rectifier block.

2. To test the negative rectifier block, follow these steps:

   1. Place the red test lead on the negative "-" terminal. Place the black test lead on the following rectifier terminals: "AC1" (3), "AC2" (4) and "AC3" (5). All readings on the meter should be between 0.4 and 1.0.

   2. Place the black test lead on the negative "-" terminal. Place the red test lead on the following rectifier terminals: "AC1" (3), "AC2" (4) and "AC3" (5). In all cases, the meter should read "OL" (overload).

3. To test the positive rectifier block, follow these steps:

   1. Place the red test lead on the positive "+" rectifier terminal. Place the black test lead on the following rectifier terminals: "AC1" (3), "AC2" (4) and "AC3" (5). In all cases, the meter should read "OL" (overload).

   2. Place the black test lead on the positive "+" rectifier terminal. Place the red test lead on the following rectifier terminals: "AC1" (3), "AC2" (4) and "AC3" (5). All readings on the meter should be between 0.4 and 1.0.

Note: A shorted diode can cause damage to 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.

Note: This rectifier block also contains varistor "CR7". "CR7" can be checked by measuring the resistance between the positive "+" rectifier terminal and the negative "-" rectifier terminal. The resistance should be a minimum of 15000.