Message: 3 Date: Sun, 26 Apr 2009 23:38:28 +1200 From: Mike van Bokhoven <mike at fenz.net> Subject: More broken Apples... To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org> Message-ID: <49F447B4.1000708 at fenz.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Well, I dragged those Apple IIs out of storage, and spent this evening poking at them, with some success. Thought I'd post my results here, and hope that someone has some suggestions for me. There are three machines in total; one an Apple II Europlus, the other two generic II+ clones. The first thing I did was run them up - all dead, garbage on the screen. Same as last time I looked at them. Step 2 - pull all the cards and try again. After that, one of the clones ran up fine; turns out that the 'language card' (16k memory expansion) was killing it. Good stuff - one running Apple II, even if it's not an original. Unfortunately, the other two weren't quite so cooperative. I decided to look at the other clone first, as its behaviour was pretty interesting. The screen was entirely full of apostrophes to begin with, but randomly, blocks of them would change to lower case 'p's, and back, flickering very quickly. It responded to a reset by changing the pattern of ps, though they tended to appear in the same place. I found the ASCII values interesting: ' = 0x60 = 0110 0000 p = 0x70 = 0111 0000 So, on reset, perhaps it's clearing half the bits per byte, and the other four have a problem. Reseting the machine tended to lead to random behaviour for a bit, such as random display changes, and speaker clicks. At one point, the display switched to high-res mode, and I could see that a large amount of memory had the same sort of pattern through it, and was flickering the same way text was; I guess the entire memory space is like that. Perhaps bits 5 and 6 are permanently stuck. I checked the CPU's behaviour; on reset, the address and data lines would run for at least a short time, so I'm guessing the CPU is likely to be OK. Often they would continue to run, at which time I'd see the flickering. Other times, activity would stop, and the flickering would also stop, usually leaving a screen full of 's. So, my next step is to track down a schematic for the machine, and see what I can figure out. I'm guessing I should look first at anything that deals with the high four bits of memory. Thoughts, suggestions and intuitive guesses welcome!