I recently picked up an Apple II+ clone, the type with the built in language card and Z80 softcard, and it wouldn't boot at all, only displaying rubbish characters. I replaced some 74161 counters that were dead and installed a modern power supply, and the computer still wouldn't boot. After scrubbing the ROM card contacts and unplugging the keyboard, I heard a beep and saw the BASIC prompt on my television! However plugging the keyboard back in caused the speaker to beep rapidly and a different rubbish pattern appeared on the screen. Rebooting the computer and unplugging the keyboard returned me to the BASIC prompt. I tried spraying deoxit into the sockets for the keyboard and character ROM but it didn't help. The prior owner of the computer installed the shift-mod, but unplugging that didn't do anything either.To sum up, the symptoms when the keyboard is plugged in are:
- Rubbish graphics on screen (continuously scrolling)
- Speaker continually beeps
- ctrl+reset causes the beeps and scrolling to stop, but trying to type doesn't seem to do anything
- Keyboard and character ROM sockets treated with deoxit
- Shift-mod unplugged
- Holding ctrl+reset while booting
If it weren't for the numpad I would have bought the Cherry MX compatible replacement, since the SMK switches in it genuinely feel awful. Looking for some advice on how to diagnose the issue, thanks!