On Mon, 10 Jan 2005 20:26:21 GMT, golf wrote:

I bought a surplus GE motor with a PWM (Pulse Width Modulation)
printed board. The board now causes the motor to vibrate and run
rough, particularly noticable at low speed on my lathe.

Try getting it repaired (probably not by GE). The usual failure mode
is one of the output MOSFETs in the bridge circuit, which keeps the
motor "running" but gives the vibration you describe. It's not a hard
fault to detect, nor to repair - any reasonable electronics person
should be able to sort it.