Apple II over-current issue

On 30/08/2011 1:04 p.m., Mr Ian Primus wrote: Well, as it turns out, it's a bit more puzzling than that. After finding that removing the RAM didn't help, I decided to take a closer look at the board. First step - remove the top shell of the case. I'm always careful about this, because it's pretty easy to damage the keyboard cable if you just pull everything off. So, I was surprised to find that the keyboard cable wasn't plugged in at all, just floating loose. Also a bit concerned, because obviously the machine couldn't have been working like that, though the seller said it was working before being put into storage. Oh well. On the upside, the short to ground had now mysteriously vanished, allowing the PSU to start up fine. Don't we all love faults that disappear on their own... well, no, we don't. Anyway, I now had a board that takes power, so I refitted one row of RAM to give it 16k, and powered it up again, hoping for a happy beep and video display. Optimistic. As it turns out, it now goes -click- from the speaker, and I saw a fixed but apparently random (and different each time i switch the machine on) pattern of dots and dashes on the monitor. And, for some reason, three of the four 74S161Ns (at D11, 13, 14, I think they drive the video output) get far hotter than I'd expect. I pulled the RAM again just to see what'd happen, the behaviour stayed exactly the same. So I figured I'd just replace the 161s with known good ones; the pins on all four looked a bit corroded anyway, so probably a reasonable idea. Having done that, I got a recognisable video display, though it's still not running properly - just a bunch of ? characters, even after fitting RAM. As it turned out, it was the cold 161 that was faulty, the ones that became worryingly hot appeared fine (checked by fitting them to another II+ board, just to make sure). So, I guess that's progress. Next thing I'll do is test some RAM for the machine, make sure I give it a good set of 4116s to work with, and go Cheers, Mike