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Appendix D: Diode Troubleshooting and Replacement
The silicon diode may be a source of trouble. The function of the diode is to allow the flow of current through it
in one direction only. If the polarity of the conducting current is reversed, the diode will block the current flow.
Thus, the diode has a low resistance to current flow in one direction and a high resistance to current flow in the
other direction. Therefore, a simple ohmmeter may be used to test the diode. The procedure for checking the
silicon diode is as follows:
1. Isolate one end of the diode by disconnecting the wires attached to the nipple (or pigtail) end of the diode
(only one end of the diode must be disconnected).
2. Clip one lead of the ohmmeter to the nipple (or pigtail) lead of the diode. Clip the other ohmmeter lead to the
aluminum heat sink.
3. Note the ohmmeter reading. Then reverse the leads between the diode and heat sink assembly. Again, note
the ohmmeter reading. If the diode is good, the ohmmeter will indicate a high resistance in one direction and a
low resistance with the leads reversed. If the diode is shorted, the ohmmeter will read near (0) resistance with
the leads in either direction. If the diode is open, the ohmmeter will show infinite resistance, indicating an open
circuit with the ohmmeter leads in either direction.
4. All diodes must be checked in the event that more than one diode is defective.
5. If the diode is defective, contact La Marche for complete heat sink replacement.
