A friend of mine has asked me, in desperation, if the list
has any comments about his circuit.

http://home.clear.net.nz/pages/joecolquitt/12vmotor.html

The problem he's got is that this circuit tested OK on the bench,
and 2/3rds of the finished units seem to be alright in use, but
the others fry all 3 FETs short circuit, causing the motors to run
full tilt, causing a scramble to disconnect the battery. It even
happened twice this week, on separate occasions, with units
that were seemingly turned off, then spontaneously burst into
life a few minutes after being used. I've suggested a varistor
across the FETs, but that doesn't explain why the units start
on their own. Any clues ? (personally I'd have made the circuit
more fail-safe, but he's very cost-conscious. Perhaps to the
extent of false economy it seems)

TIA

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