Sounds like something is shorting out you can try to continuity check between GND and vcc when no power is applied but my guess is difficult or not worth repairing most likely. Hard to guess without hands on debugging and even then toss up on if I'd be able to find and/or fix the short. I've heard F7 boards run pretty hot but haven't really checked mine out in terms of temp (have a kakute f7 on a couple copters)