voltage where I shouldn't have voltage

[kroy1968]

I'm diagnosing a 99 txt series cart and I'm using the diagnostic posted on here by Scottyb.

When I get to this step:
CHECKING CONTROLLER OUTPUT Connect (-) probe to M- terminal.
Connect (+) probe to B+ terminal.
The reading should indicate approx. 0 volts.

I have full voltage during this test. Same as battery pack 37 volts

I've checked and rechecked that the cart is wired correctly.

[JohnnieB]

You may be reading a phantom voltage due to the high impedance input of your DVM, or the MOSFETs in the controller are shorted, or there is some conductive crud between the controller's B- and M- terminals.

I'm not overly fond of measuring the voltage between M- and B+ since bad cables, bad F/R switch and bad motor all produce the same voltage readings, but it is useful when checking if the PWM output of the controller is going to 100% duty cycle.

For initial troubleshooting, measure between B- and M-. Should be full pack voltage when pedal is pushed just far enough to make solenoid click and decrease to near zero as pedal is pushed to floor.

[kroy1968]

So, what if 0 voltage when solinoid clicks between B- and M-?

[JohnnieB]

Originally Posted by kroy1968

So, what if 0 voltage when solinoid clicks between B- and M-?

Then you have an open somewhere in the high current cables, contacts or connections highlighted on the attached schematic.

Leave the black test lead connected to the B- terminal and go looking for battery pack voltage at the various high current cable connections. When you find the voltage, the problem is between the last place there was no voltage and the first place there was voltage.

The F/R switch is shown in F.

----------
When high current circuit is intact and the pedal is pushed just far enough for the solenoid to click, the MODSFETs in the controller don't pass any amps to the motor, so they are effectively an open and the full battery pack voltage will be dropped across them (B- to M-). If not, there is an undesired open in the high current circuit that isn't allowing the battery pack voltage to reach them.

Electrically, the high current circuit is a single piece of wire with some lumps in it. Granted, it meanders all over the place, but it is still simply a series circuit.