10EE round dial electrical issue

Yesterday my lathe failed to start normally. It's a 1962 round dial with the original MG. Pressing the start button results in a loud persistent humm without the motor starting. The humm persists until the stop button is pressed. The motor starter's normal click is heard. I made a short video in case the tone of the humm is indicative of something.


I removed the motor starter cover and measured the input line voltages, and they are identical to those measured during my previous unrelated reported problem back in May. So the rotary phase converter can be ruled out. I didn't measure any voltages on the output side of the starter not knowing how safe it is to leave it connected for longer than a few seconds at this point.

One other clue. Earlier in the day I was using the lathe and the motor slowed down without my moving the switch. I turned off the spindle and then it came up to speed.

Rotor could be stuck on the MG check that.

That sounds like you dropped a phase into the MG motor.

Started by checking all the screws in the motor starter compartment (none seemed loose) and then measuring the voltages past the start block as advised. I had to interrupt that work, and when I came back and pressed the start button, everything started up normally. Maybe the gremlin decided he'd had enough fun for one weekend.