I have a 400k drive like this, except it will just flat out die when it warms up some (I got it to work for a few minutes, but it became unresponsive and crashed the system). By trial an error swapping parts from a known working drive led me to a somehow faulty motor controller. Not saying that's your problem, but it could be?

Try swapping PCBs around from a known working drive and see what happens.

c