It would help if you could be a bit more specific as to what the problems are and why you think it is beyond help. It could for example simply be that it needs a new speed control potentiometer if it is "temperamental" – that implies that sometimes it works and sometimes it doesn't. Yes that controller might do the job, looks the right sort of rating. Note that it has provision to drive a field winding which you might or might not need on the machine motor.

Symptoms plus a couple of photos of the inside would help, it looks like a nice machine and well worth preserving.

OK, sounds sensible then. Probably the existing controller is a thyristor or triac type, similar to the eBay one. The eBay controller is probably floating so you need to take care when installing it, and check that the original design does not assume the controller is grounded. On that controller, you'll see that one end of the potentiometer is labelled GND but I suspect that this should NOT be connected to mains ground, it just means the common end of the pot. As I said, some photos of the current device showing the wiring, terminal blocks etc would be useful. Given your professed competence in electrical matters, it would be well to get someone who knows more about electrics to have a look!

Thanks. The German words "metallteile der electronik führen spannung" mean "metal parts of the electronik carry voltage" – as I suspected the controller floats at mains voltage. It also looks like there are a few ICs on it so quite complex, it probably has a speed regulation function as well as control, to keep the speed constant under load. I'm not sure if the eBay controller will have this – on my little CNC mill I use a KB Electronics controller which does.

**LINK**.

That's the U.K. Stockist and the version that on a quick look seems best for your motor. I've sent you a PM.