Quark fried, blown capacitor...

[BrianG]

Those Trancil diodes seem like they might help to clamp the back-emf pulses from getting to a really high value, especially with high-inductance motors. I just wonder how much power they can absorb. It's hard to see the underside of the board, but I don't think either Quark or the MM use them...

Personally, the only thing I'd want to do is add a little more capacitance on the input so the existing caps don't have to work as hard.

It's too bad these controllers pull so much current in a way, because I think a low turn coil on the battery lead would also help supply a bit of current boost as well as filter the ripple from the batteries. That in conjunction with the input caps would create an LC filter. Unfortunately, the wire would have to be quite thick (or even use Litz wound coil) and may even need a ferrite core to concentrate the flux, but then the controller would start getting kinda heavy.