Turn off power and remove the PCB's one at a time starting with the big one. Look for cooked tracks, which is then an indication something went to ground where it shouldn't and that will usually be far removed from where the burnt tracks are. The burnt tracks are a result of the short. The problem is that most parts of the motor control circuitry is at high voltage and ANY PART of the circuitry except the (opto coupled input to the big board) being momentarily shorted to ground destroys something. If you have any burnt tracks, it is very likely that the hall sensors in the motor will be dead too.
The damage will probably be obvious but what caused it may be obscure.
Examine with care not to disturb the evidence.
It is easy to get the smoke out, but hard to get it back in again. (oops sorry) My brain just threw a wobbly.