Can't really add much over John's useful suggestions. It seems clear now that there is a fault beyond the chip - this second failure suggests the first chip didn't just expire for no reason. So checking for decent connectivity to each physical pin using a multimeter could be worthwhile. Ideally right to the motor connections, and to the other connected components on the board. Maybe an intermittent fault though, like a cracked PCB track, which may measure fine most of the time, but open up as things get warm.

Maybe it is time to get new electronics as you say? Particularly if the risk of failure is costly to you. I hate to waste perfectly serviceable kit, but sometimes pragmatism has to take over!

Cheers
Graeme