This is the cure for several makes of sewing machine if your foot controller has just gone pop with a puff of smoke or the machine runs on full speed all the time.

The suppressor capacitor in the pedal has failed, short circuiting the switch contacts, leaving the machine 'on' all the time.

There are many models of pedal and machine that use this capacitor.

The part supplied may be from a different manufacturer than the original part fitted, although it is an equivalent part.

Rating 150nf 275V Class X2

In most cases, you simply open the pedal and replace the capacitor either by unscrewing the old one and replacing it with a new one or de-soldering it and soldering the new one in place.