The wiring for Macs is so small and fiddly being systematic and cutting the problem in half is important. My normal troubleshooting steps for something like this were:
- Unplug the cable from the motor in question and plug in into a known working motor. Plug the known working motor's cable into the motor in question. This may require the use of some jumper cables to reach, but if possible use the existing cable to drive the known working motor so you are testing all of the components of the effect you're trying to troubleshoot. Run both effects in manual mode and see where the problem goes.
- If the problem goes to the previously known working motor then it's a control problem. I always suspect cables first so bypass the existing cables with jumpers, then work down the line to driver boards.
- If the same motor doesn't work the issue is there. Disconnect everything from the motor and try to run it. If it spins normally with nothing attached look for a physical issue preventing motion (did a tab get left bent up when the hardness was replaced for example). Look closely there might be something increasing friction, but not completely blocking travel. If the motor doesn't spin with no load attached it's either the motor or the cable has chosen that exact moment to fail (did I mention I hate the wiring harnesses in Macs?).
Failing all of that I have a video for you showing how to properly maintain a
Mac fixture.... from a high
point... off a
loading dock.... using gravity.