[dtengineering]

Wow. What a weird situation. We're in our third year now, and, over the years have hooked up many Victors many times. We've only "toasted" one. (Usually my students are much more efficient at breaking stuff!) I keep it on my desk to show the students how quickly a hundred dollar bill (and change) can go up in smoke.

It happened late one evening in our rookie year... we had pulled the electrical board apart, re-wired it, and put it back in the robot. It was late, we were tired... I didn't check, and the students didn't notice that all three Victors on the board were backwards.... the motor connections were attached to the power supply side and vice-versa.

Amazingly they ran (very little load, the robot was up on blocks) for a little while, but slowly... when one stopped responding we realized we had a problem. Again, to IFI's credit, only one of the three was blown... a good thing, as we only had one spare, and no money to buy more.

The blown Victor had cracked FETs, just as you describe. I haven't tried replacing them... in some ways it has more value as a warning than it would as a functional speed control.

So if your motors were under load when you hooked them up, and the Victors were backwards, that might have caused them to fail instantaneously.

As for the sparking after you disconnected all the wires... totally weird. The only thing I can think of is that when you mount them to a board using #8 machine screws that the machine screws come very close to the power hook ups on one corner. Last year we switched to nylon screws to save weight and reduce the chances of shorting.

Our condolences on the loss of your Victors. Hopefully you have the time and resources to replace them.

Jason