I'm working on a Diner now and had almost the exact same problem. Perfect lower display, but spotty upper. My voltages checked out, 39k resistors were perfect and zener diodes right on. I switch out my Earthshaker display after checking all those things as a last resort. Worked like a charm, so I just ordered a new Pinscore display from Marco's yesterday. Sucks not being the $1 fix, but probably the original display in these games, so I guess $200 for another 20 years of service isn't too bad.