Anyone know how these work?
The foot control of my wife's 1980's Singer sewing machine started emitting smoke a couple of days ago and, at one stage, the motor ran without having her foot on the pedal.
Mr Google suggests that it contains a capacitor which, if it develops a short circuit, can exhibit these symptoms. I opened it up to have a look and there was was a nasty smell from the vicinity of the capacitor, but nothing obviously burnt out. I've ordered a new capacitor, anyway, and will fit it when it arrives. Meanwhile, I've blown all the dust out of the foot control with an airline, and tested it - and it seems to be working ok.
But speed control isn't very progressive - it tends to be virtually all or nothing, like a car accelerator which only has two positions. [This isn't new - it was like this before it started smoking.]
So I'm trying to understand how the speed control is supposed to work.
When the lid is closed and pressed down, a post on its underside presses down on the centre of the long copper? strip so that it makes contact with another strip below (hidden in the photo) which is connected to the brown wire - swiching on the motor. As the lid is pressed down more, the upturned part at the left hand end of the copper strip moves to the right and presses on the spring-loaded carbon rod. I assume that it is somehow meant to increase the motor speed, but I don't understand what's going on inside the ceramic cylinder.
Can anyone throw any light on this?