View Full Version : OT Sewing Machine Speed Controller

David S Newman
01-29-2012, 02:45 PM
My wifes sewing machine is playing up, it will not turn off, the foot pedal has no control of it at all, it just runs at full speed, the only way to stop it is to turn it off from the socket. It even runs when the foot pedal is disconnected once again at full speed. Any help please ? By the way this is not a computerised machine just an old Bernina. David

01-29-2012, 03:18 PM
The older controllers were just a variable resistance pedal into a universal motor, open it and inspect the foot operated lever
If this is a later type it may have a triac control then the triac could be shorted.
Alternative is to feed the material in faster:)
I just noticed you mentioned runs with the foot pedal disconnected!! Then it most likely is a short circuit in the FP outlet, this is in series with the motor, so it should be easy to trace.

01-29-2012, 06:01 PM
I don't know those machines, but it's certainly possible that the speed control circuitry, if electronic, is inside the machine. In that case there may not be a wiring short, but could be a triac or scr short, or it could be an open in a circuit. You wouldn't think the manufacturer would make it so the motor runs at speed with the pedal disconnected, but it still is possible for that to be the case. Is there any option with the sewing machine to not use the pedal? That would mean some kind of built-in motor controls would have to be there.

01-29-2012, 08:04 PM
Had that happen a few times on our "Treadle".

(That woman had huge leg muscles!!!):D