31
Troubleshooting and Replacing Power Silicon Diodes/Modules
1.
On the ohmmeter, set the switches on “ohms”, “DC”, and “Rx100” scale and 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). On a diode module, both of the outside leads must be disconnected.
2.
Clip one lead of the ohmmeter to the anode lead of the diode. Clip the
other ohmmeter lead to the cathode. Refer to figure on right.
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 zero
resistance with the leads in either direction. If the diode is “open”, the
ohmmeter needle will not indicate or it will show infinite resistance in
either direction, indicating an open circuit.
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 heatsink
and replace with a new diode.
4.3.4 Checking
Capacitors
1.
When checking capacitors, assure all AC power is turned off and battery is disconnected from charger.
Check capacitors with DC voltmeter to see that DC voltage is at near 0VDC.
2.
Momentarily short circuit the capacitor leads to assure complete discharge.
3.
Connect the meter test leads to the capacitor leads or terminals and observe indicated resistance.
4.
A good capacitor will indicate an initial low resistance and gradually increase as the capacitor charges. The
final resistance of a good capacitor is usually several hundred thousand ohms approaching a megaohm.
5.
Initial high resistance approaching infinity indicates an open capacitor. Initial and continued low resistance
readings indicate a shorted capacitor.
NOTE: When ordering replacement parts, drawings, or schematics, always give model number, serial number
and AC input voltage.
Summary of Contents for A36D
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