Maybe the next logical step is to put the CPU board from Firepower (currently out of the machine with Tri Zone roms installed) into Tri Zone .. along with the driver board from Tri Zone (currently out of the machine)

That will at least prove if there is a fault (eg PIA causing display issues) on the CPU board or not.

Then, if that CPU board checks out OK put both those boards into Firepower and see what happens ?