I have a Dremel Multi (model 395) which until now has had only very
light use. I recently had a 'proper' use for it - cutting a square
hole in a steel plate (1mm think or so). I bought some diamond cutting
wheels for the dremel off eBay and set to work. I wasn't going 'hell
for leather' and was paying some attention to allowing the thing to
stay cool-ish.

Don'tcha know it - in the middle of this job the Dremel has packed up.
Or partly ... it stops after a few seconds, seemingly losing power. It
might start up again after a few seconds, or if I wiggle the cable as
it goes into the drill, or if I use the built in switch/speed control
to cut the power, then try powering it up again. But then it stops
again after a few seconds.

I've opened the thing up and all seems well - the brushes seem OK, the
cable connections are tight, the commutator seems OK, etc.. I've seen
that Dremel do a load of spares and I wonder if anyone has experience
of what might have gone wrong. My current thoughts are maybe the speed
control unit, but given my recent poor experience of Bench Grinder
fault diagnosis (and that I guess this is the most expensive part to
replace) I'm happy to learn of common problems with these units.

Thanks
Jon N