Images show both casing halves with the motor and cam and oscillator partially removed. It's easier to undo the two screws holding in the mains cable, so everything comes away from the casing in one go.

With full access, its now possible to do continuity tests with a multimeter to find and locate a break in the circuit. In my case there was a break between one of the graphite bush assemblies (both arrowed) and one the big stator coils.

There was an in-line component hidden under the black shrink-fit insulator in the suspect connecting wire where there was no electrical continuity as found above. The shrink-fit was removed with a scalpel.

The hidden component was a small inductor coil (to filter out high frequencies?). Its connection lead had come out of the crimp with some blackening caused by arcing. The old crimp was cut off replaced after some cleaning.

I didn't have any replacement 4mm brass crimps but used what I had (15mm 4mm dia stainless tubes) and used old blunt snips for crimping. There was enough space for my larger crimp. New insulation was applied.

With the jigsaw in pieces, you could consider cleaning and re-greasing if required. Or even replacing the bushes, though mine extended 7mm and considered OK.