HOSE AS 3894073 - Caterpillar

Varistor Test
External Varistor
The following procedure tests the normal state capability of the internal varistor, CR7, that is used within a full wave rectifier diode module. If any meter reading does not fall within the given range, replace the heat sink assembly. Refer to the "Removal/Installation" instructions.
Illustration 1 g01342087
Varistor module
Remove the positive and negative leads connected to the varistor. Disconnect the resistor that is wired from ground to one of the varistor terminals.
Place the megohmmeter test leads on the varistor terminals as follows. Note: The varistor is not polarity sensitive.
Place the black test lead on one terminal of the varistor.
Place the red test lead on the other terminal of the varistor.
If the megohmmeter is not capable of reading DC voltage, then connect a DC voltmeter to each terminal of the varistor.
Select 1000 VDC on the megohmmeter. Apply the test voltage across the varistor. Note: Do not apply voltage for more than three (3) seconds.
The megohmmeter should read between 735 VDC and 910 VDC. Note: If the varistor is failed, a reflected voltage transient was most likely imposed upon the main stator and imposed upon the main rotor. As a component, varistor failure is not likely to occur. If a varistor does fail, the failure is caused typically by one of the following:
Incorrect paralleling or loss of synchronism
Reverse VAR or reverse power event
High ambient temperature (or other application error)
Large, sudden load acceptance or rejection
If the reading is greater than 910 VDC, varistor CR7 is OPEN. CR7 has failed. Replace the heat sink assembly. Refer to the "Removal/Installation" instructions.
If the reading is less than 735 VDC, varistor CR7 is SHORTED or DEGRADED. CR7 has failed or is failing. Replace the heat sink assembly. Refer to the "Removal/Installation" instructions.
Install all leads to the rectifier diode module. Torque the connections to between 2.35 N m (20.8 lb in) and 3.35 N m (29.7 lb in).