I got a hacked up Pool Sharks that I'm having trouble troubleshooting. It's the first non-EM I have worked on. When I turn on the power, it beeps three times. The left display doesn't work, but the right display says "is stuck on." Sometimes the right display only puts up a few of those letters, then over time shows all of them. When I press the test button on the MPU, it beeps 11 times, runs through lights, and solenoids, then stops and say "is stuck on." Both displays look fine physically. I would like to get the left display working so I can figure out what exactly "is stuck on." The diagnostic LED on the MPU flickers but doesn't give any discernable flashes.

Any suggestions and/or assistance is appreciated.

With the hacks and board corrosion I have found, I was hoping to diagnose whether it was the MPU or the display. If there is a problem at the MPU, LED displays aren't going to fix anything. So far I have replaced the PIA at U41 and the 4.7k ohm bussed resistor networks. That cleared up the issue with the intermittent right display but still nothing on the left display. The left display gets -89 V at the display. I'm getting -90 V at pin 1, +90 V at pin 3 and +4.99 V at pin 6 of J7 at the display.