When this happens, the pic usually just hangs up. It will not do anything until it is powered down and back up again. It happens so fast that I have not been able to catch it on the scope. It has blown up the 15V power supply before, which is even more strange. The 15 V supply is isolated via an opto to drive an IGBT only. Like I said this all works fine on line power, but when they use a generator things go bad. If they are using the pot instead of the external 0-10V control everything seems to be fine on line power or the generator.

Thanks for the input.

Terry