Traded my working Flash CPU to someone a few weeks back, and pulled a old broken one from the pile. Put in some new memory, changed out a couple sockets, and it was passing leon's tests. I stuck it in the machine. The LEDs flashed once, and the audits stuff came up. It was acting like I was holding down the black button, with the numbers continually climbing in the bottom display. I turned it off, and checked the diagnostic switch plug lines. They were fine. I then turned the machine back on again. Nothing on the displays. Tried resocketing the PROM to no avail. I thought maybe the machine was booting fully, but I wasn't turning it on and off fast enough for it to go into attract mode. As part of testing this theory, I held down the black button again. Miracle of miracles, the audits screen appeared. I let go of the button. The audits screen vanished. A little further testing revealed that holding down the button also turned a few feature lamps on at the same time as the audits screen.

I'm a little baffled as to what would cause this. I can read the schematics. But what line controls displays being on and off? How would that line be related to the diagnostic switch?