[philso]

Either one of the wires in the PWM cable may have a poor connection or the SPIKE is damaged.

Make sure that the PWM cable is seated all the way into the spike with the black wire (- on the Digital Sidecar) next to the "B" on the SPIKE.

Pull the PWM cable out completely. Check each wire end-to-end with an Ohmmeter to make sure there is not a broken wire.

There may be a dirty connection. Unplug and replug the PWM cable 5-10 times at each end. Try rubbing a red pencil eraser on the pins of the PWM cable to clean them.

Set your voltmeter to DC Volts. Hold the black probe on the pin with the black wire of the PWM cable. Hold the red probe on the middle pin and have your software enable forward then reverse. You should see about +4 V in one direction. Move the red probe to the third pin and have your software enable forward then reverse. You should see about +4 V in the other direction. If this is OK, your signals are getting to your SPIKE but it is not responding due to a bad connection between the SPIKE and the PWM cable or damage to the SPIKE.

In the "Braking Mode", both relays in the SPIKE should be energized. Set your voltmeter to DC Volts. Put the black probe on the "-" terminal of the spike (input from the PD Board). Put the red probe on the "M+" and "M-" terminals. You should see +12 V relative to the "-" on both output terminals.

It is possible that the circuitry for one direction is damaged in your SPIKE. The circuitry for forward and reverse are largely independent so it is possible to have a SPIKE where only one direction works. Replace it with another SPIKE.

I just noticed Mark has posted similar advice.