Adrian Brentnall wrote :
Anyway - last week, said motor gave a gasp and died. Now all it will
do is buzz weakly - and won't turn - mains lights in the workshop dim
while it's buzzing (not a good sign, I think).

If there is no sign of damage/ burnt windings on the motor, then I
would guess that it is the starting capacitor which has failed.

The grinder motor which you bought to try to replace it, doesn't have
anything like as much torque as the capacitor start motor you had -
hence its difficulty at startup.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk