A fella has asked me to have a look at his lathe to see if I could fix it:

LeBlond, with a variable speed DC motor drive that uses a motor-generator and some electronics. I don't know the model number, I do know he runs it from a phase converter. He has the schematics, and I do have some electronics experience.

The problem is that the speed "hunts", IE speeds up, then slows down.

I've not actually seen the machine yet, but was hoping that someone here might have experience with it and could point me in the right direction so I'd appear to be brilliant. :-)

Will probably have further questions once I get my hands on it.