TECH: Red Baron Troubleshooting Question

First a short run down:
Game played but the display was expanded off the screen, could not
read the scores etc.
Placed game in test and found bad RAM at C1.
Replaced with AM91L24BPC
In test, no RAM errors but display still off screen.
Now no display in play mode.
Tested voltages on AVG section, found bad 7815 (putting out +22vdc)
Replaced VR1,VR2,VR3 and all electrolytic caps on AVG PCB (a 100uf25v
cap was tested at 2.86uf)
Now display in test is normal, no longer expanded off screen but now I
can see that PROM E1 shows bad.
Another thing is that the start button is lit and the stick does not
change the output on the screen in test, (it did for a moment then
went back to 255/255)
When pressed, the fire and start buttons produce tones
I also noticed the X-istor on the heatsink of the A/RII got really hot
while I had the game in test, it cooled down quick after the game was
powered down
Finally the question:
Could the bad PROM cause the screen not to display as well as keep the
start button lit and prevent the stick from changing the output on the
display in test OR did the bad VR and cap cause more damage somewhere
else?
Any ideas would be helpful.
Thanks in advance.
Jeff

Since the software is in the PROM, a failure can cause all
kinds of problems. Do a checksum on the bad PROM, and
replace it if needed. Go from there.

When dealing with these boards its best to fix all of the
obvious problems first.

Steve