TROUBLESHOOTING AND REPLACING SILICON DIODES
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 pig-tail) end of the diode. (Only
one end of the diode must be disconnected.
2. Clip one lead of the ohmmeter to the nipple (or pig-tail) lead of the diode. Clip the other ohmmeter lead to the
aluminum heat sink. (If a portable multimeter is used, set the switches on ohms, DC and scale RX100
3. Note the ohmmeter reading. Then reverse the leads to the diode. Again, note the ohmmeter reading. If the diode is
good, the meter will indicate a high resistance in one direction, and a low resistance with the leads reversed. If the
diode is shorted, the meter will read full scale, or "0" resistance with the leads in either direction. If the diode is
"open", the ohmmeter needle will indicate or 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, remove the defective diode from the heat sink and replace with a new diode. When
installing a new diode, be sure to note if the old diode was insulated from the heat sink. If the diode should be
insulated from the heat sink, care should be taken so that the mica insulating washer is placed properly on each
side of the heat sink with the insulating bushing between the diode mounting stud and the aluminum heat sink.
WHEN ORDERING REPLACEMENT PARTS, DRAWINGS OR SCHEMATICS, OR
REQUESTING SERVICE INFORMATION, ALWAYS GIVE MODEL NUMBER, SERIAL
NUMBER, AND A. C. INPUT VOLTAGE.