If you haven't cleared the machine it should be a simple matter of inserting the new MPU and clearing a couple errors with the jackpot reset key. When the error comes up after booting, open the main door and an alarm will sound, then turn jackpot reset key 3 times at which point an instruction to hold the reset button for 3 seconds will show up on the VFD display. Follow the those instructions and if the machine shows up with a second error, repeat the process. After 2 cycles the machine should be fine with whatever settings were on it before the board went bad