SR4 Generator with VR3 or VR4 Voltage Regulator Caterpillar

Six-Diode Rectifier Block

Illustration 1	g00613957
Six-Diode Rectifier Block (one piece) (1) Positive Rectifier Block (2) Negative Rectifier Block (3) Rectifier Terminal "AC1" (4) Rectifier Terminal "AC2" (5) Rectifier Terminal "AC3"

The following procedure tests all six diodes within the 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. 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 ohms.

3. Place the red test lead on the negative "-" rectifier 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 ohms.

4. 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).

5. Place the black test lead on the negative "-" rectifier 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).

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 ohms.

Two-Diode Rectifier Block

Illustration 2	g00610186

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

2. Place the black test lead on the AC rectifier terminal.

   1. Place the red test lead on the negative "-" rectifier terminal. The reading on the meter should be between 0.4 and 1.0 ohms.

   2. Place the red test lead on the positive "+" rectifier terminal. The reading on the meter should be "OL" (overload).

3. Place the red test lead on the AC rectifier terminal.

   1. Place the black test lead on the negative "-" rectifier terminal. The reading on the meter should be "OL" (overload).

   2. Place the black test lead on the positive "+" rectifier terminal. The reading on the meter should be between 0.4 and 1.0 ohms.

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.