You really should find some boards that you don’t need or don’t mind if anything happens to them and practice heating and pulling various components off from it and eventually you will get a very good idea of exactly how much heat you need to remove components without causing damage to the board. Keep practicing until you can remove them without scarring or burning the board and practice cleaning areas with solder removal rope.
I was about to answer this with almost the same advice accept I was going to say if you replace the I/O board (power) board and it still continues to do the same thing it has to be grounding someplace else from the logic board. If you don’t have the equipment to test for this you could remove the logic board and make sure that there is something between any point where the logic board sits on a mounting point and is not metal to metal.
