
Section 4 • Repair Procedures
August 2016
Part No. 218567
AL4 • AL4000
4 - 11
How to Check a Generator Diode
DANGER
High voltage. Exposure to
electrical wires or electrical
current will result in death or
serious injury. Remove all rings,
watches and other jewelry. Turn
off all power when not needed
for testing. Use extreme caution
when working with high voltage
electrical components.
DANGER
Electrocution/burn hazard.
Attempting to service the machine
before the capacitor is fully
discharged will result in death or
serious injury.
Note: Be sure the engine has been turned off for
at least 15 minutes before servicing the machine.
Use a voltmeter to confi rm there is no residual
voltage in the capacitor.
1 Remove the fasteners securing the end
cover/bearing housing to the generator.
Remove the cover.
2 Locate the diode at the end of the generator.
3 Tag and disconnect the positive wire lead from
the diode.
4 With a multimeter set to test diodes, connect
one multimeter lead to the diode terminal
and the other multimeter lead to the 'Q' lead
terminal of the generator. Note the results.
Note: Refer to the instructions which are provided
for your multimeter to ensure the diode is
accurately tested.
5 Reverse the multimeter lead connections. Note
the results.
Result: The two readings are at a ratio of
3000:1 or higher. The diode is good.
Result: The two readings are at a ratio of less
than 3000:1. The diode is faulty and should be
replaced.
Note: Before installing a new diode, clean the
surface of the exciter rotor core, and run a bead of
a thermal-electrical compound around the base of
the diode (the threads of the diode should not be
coated). Torque to 20 to 30 in-lbs / 2.2 to 3.4 Nm.
GENERATOR
Discount-Equipment.com