I'm having a go at restoring one of the "parts" System 80s I got off Kenneth (old_system_80_user) a while back.
It's proving to be a challenge. For the main board, I thought I'd had it sussed when I identified and replaced a RAM IC which took it to it's proper 32k. Despite passing all RAM checks the machine does weird things, especially when a key is pressed ...but not when at the command level in BASIC?? More when programs are running. This includes feezing, returning to READY?, inserting prompt lines were they shouldn't be and (most weirdly) simply returning to the command level (i.e. the ">" prompt in BASIC) (Very alarming when you are in the middle of playing Seadragon).
That's just the board. The internal cassette is also proving difficult. It shows a signal sometimes and at other times, not at all? Occassionaly it will have a signal on load, only to drop to zero level 1/2 through loading? I've replace EVERY capacitor on the analogue board PLUS the quad op-amp and transitor AND resoldered every connection. What else is there!
Oh it doesn't record either.
Power levels going into the cassette deck seem to be normal and are very similar to a good working unit?
Regarding the computer itself, I do wonder if those issues above might have something to do with power? There is no obvious sign of power problems (screen is steady etc.) but there might be something intermittent lurking. I'll do some checks tonight (including a check for AC ripple), and also swap it with a "known good" power unit.
Why am I posting all this? Probably just to get it off my chest but if anyone has any ideas, I'm receptive.