This is the progress report on the Apple 1 we are restoring. I'm wondering if anyone has any insights as to what our problem is. We think the 6820 PIA may be bad. But finding an original looks hard right now so we are going to try the 6821. Will this work? The following is from Larry Brown the engineer doing the restore.
I’ve been working on the board for a few days but have not had much success. The processor appears to be running and the video display also appear to be working but the data from the character data 6820 PIA to the video display doesn’t seem to work. Also the keyboard data doesn’t seem to reach the processor but it appears to be polled so there in no interrupt to confirm for sure. The PIA IC also has several wires running to the IC socket in the breadboard area so static damage is a possibility.
At this point, all I can come up with is to replace the 6820 PIA. Apparently they were long ago out of production, replaced with 6821 and the newer 68C21. Next thing to do is order a test 6821 IC. If it fixes the problem, we can search for a vintage part. Just in case, a spare 6502 would be good to have. This is turning into quite a project.
Supposedly pin compatible 6502