This was a VERY specific case that might not apply to you. Are your transistors blowing? Do you smell smoke? Or is a pop simply not working?

Always check the simple stuff first - a loose wire to a lug or a switch, a misadjusted switch, a bad coil (jump it with alligator clips to one of the working coils and see if the coil is dead or not). Once you do all this stuff you can start worrying about transistors, or wiring continuity to the boards/connectors themselves.