Quoted from DuffysArcade:
Start at the beginning...verify good voltages on the power supply. Check the interconnect cable between the MPU & Driver board. Verify you have sufficient grounds at both boards. I'd bet it's one of these issues.
At the power block in the bottom of the cab I get 4v on the 8v terminal, 20v on the 25v. On the Gulf Power board I’m reading correct values on all the terminals. The interconnect cable reads continuity between the MPU and driver on all pins.