The chances are that your foot-pedal is at fault and could need replacing.
Or if you are confident about delving into the internal workings of something electrical, you could well find what is going wrong with your machine in there.
FIRST OF ALL. BE SAFE. Unplug it from the mains first.
There is one small screw to the rear of the pedal on these machines.
Undoing that will allow you to separate the top and the bottom casings of the pedal. lifting the back first then the front.
Though the power lead will not allow them to part completely, it will be enough to allow you to see clearly what is inside.
You will see a very simple mechanism in your top casing with the sprung pedal on the outside there is a small tang (or lever) that comes through from the pedal to the inside of the case.
Move your pedal up and down to see this tang move inside the case.
When upper and lower case are together, this tang connects with, and moves a longer pivoted arm in the lower case. This arm is the contact, which slides along the top surface of the wire coil (wound around a flat white ceramic block,) and also contacts with a curved copper strip assembled just above it.
When viewed from the side you will see the pivoting arm has two thin sprung contacts at the end. One contacting the wire coil, and one to the curved copper strip.
The point at which the sliding arm contacts the coil at any one time is what dictates the voltage, and therefore the speed of your motor.
It is possible that this sliding contact arm is not being allowed to return fully to it's correct resting position, where it should no longer be making contact with the coil.
This could be why your machine is running on after your foot has been taken off the pedal.
Ensure the little tang sticking through from the top case is actually slotting into the small 'C' shaped plate at the top (pivot end) of the sliding contact arm.
It may be that your pedal has been dropped or damaged, or has been incorrectly reassembled in the past.
Check the sliding contact arm moves freely the whole way along the width of the coil and that it remains in contact with both the coil itself and the curved copper contact strip above it, and return it to its resting position fully over to the right hand side.
Before reassembly, remove any fluff and dust by lightly brushing with something like an old an toothbrush. (NOT a wire brush) If there is any fluff or grease on the coil or contacts this will interrupt smooth operation of the machine, so lightly clean in between the contacts with a piece of paper being careful not to bend or scratch anything.
Re-assemble top and bottom case ensuring the tang in the top case is locating in the 'C' shaped plate on the sliding arm. This should happen naturally as long as nothing has been bent.
The front of the case should be put together first, pushing the back down ensuring nothing is trapped or misaligned. Before replacing the screw check the pedal is operating smoothly.
There is also a limiting screw in the case underneath the pedal which you can screw out to limit the top speed of your machine if it shakes at full speed like mine does.
I hope this helps.
Allan Edwards, May 2024
