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 TM 55-1905-220-14-10
5-44. 24 VOLT RECTIFIER-MAINTENANCE INSTRUCTIONS.
LOCATION
ITEM
ACTION
REMARKS
REPAIR (Cont)
TROUBLE SHOOTING 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 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 the other direction, and a high resistance to current flow
in the other direction. Therefore, a simple ohmmeter may be used to te6st 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 "O"
resistance with the leads in either direction. If the diode is "open", the ohmmeter needle will not
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.
5-646
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