PLATE 4865117 - Caterpillar

Illustration 1 g03792564
Typical example of diode connections (1) Positive diodes (2) Negative diodes
Disconnect of all the diode leads from the exciter rotor. Refer to Illustration 1.
Illustration 2 g03791400
Use an ohmmeter to measure the resistance of each diode in both directions. Note: When testing diodes, observe the polarity of the test terminals in regard to polarity of the diode. The polarity of the diode is indicated by an arrow on the diode. Refer to Illustration 1.Current flow is only from the anode to the cathode. The diode is considered good when:
The diode has low resistance, up to approximately 100 ohms, in the forward direction
The diode has high resistance, approximately 1 M ohm, in opposite directionDiodes that have a resistance of zero ohms or greater than 1 M ohm that is measured in both directions is defective.In most cases, the ohmmeter test of the diodes is sufficient to identify faults in the diodes. In some extreme cases there may be a need to apply the rated voltage to ensure that the voltage is blocked. And there may be a need to apply the rated voltage to detect current flow for detecting fault in the diodes. If there is any doubt about the status of the diode, call your technical communicator.