Curtis PMC 1204X/1205X/1209/1221 Manual
31
TROUBLESHOOTING & BENCH TESTING
TEST
4 Check for controller output
4-A The first step is to measure the output drive voltage to the motor at the
controller’s M- terminal.
4-B Connect the voltmeter (+) lead to the controller’s B+ terminal. Connect the
voltmeter (-) lead to the controller’s M- terminal.
4-C Turn on the keyswitch with the forward/reverse switch in neutral, and then
select a direction and watch the voltmeter as you depress the pedal. The
voltmeter should read zero (or close to zero) before you apply the pedal, and
should read full battery voltage with the pedal fully depressed. If it does not,
the controller is defective and must be replaced.
4-D The next step is to measure the current in the controller’s M- lead. If you have
a means of measuring this high dc current, such as a shunt/meter setup or
a clamp-on dc ammeter, use it. If not, we recommend that you buy an
inexpensive ammeter of the type that is simply held against the wire being
tested. These are readily available at auto parts stores, and their accuracy is
adequate for this test.
4-E Turn on the keyswitch with the forward/reverse switch in neutral, and then
select a direction and watch the ammeter while depressing the pedal.
4-F If you see no current flowing in the M- lead, the problem is an open circuit
in the motor or the wiring between the motor and the controller. Check the
forward/reverse switch. If your vehicle uses contactors for reversing, check
to see that they are operating and that their contacts are closing. If these are
okay, check the motor armature and field for opens.
4-G If you do see a high current flowing in the M- lead, but the motor does not
turn, the problem is a short in the motor circuit, a miswired motor, or a short
in the controller’s internal plug diode. Test the plug diode as follows:
1. Remove power by opening the battery circuit. Take the
cable off the controller’s A2 terminal.
2. Use an ohmmeter to check the resistance between the
controller’s A2 and B+ terminals. You are testing for the
presence of a diode inside the controller, so swap the two
leads of the ohmmeter and look for a low resistance one way
and a much higher one the other way. If your meter has a
diode test function, use it.
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