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Macintosh IIsi bank A RAM issues
Posted by: 8bitbubsy on 2023-07-03 07:09:01
I have a Macintosh IIsi that would give the sad mac chime since it had severe issues with onboard RAM (bank A), so I desoldered the RAM chips and their bus transceivers (74ALS245AD) as they were corroded anyway. The board now chimes and boots from floppy or HDD, but I get a black screen. It syncs, but the picture is all black. I didn't have the right VGA adapter before, so I couldn't test if it gave a video output before I desoldered all the stuff.

This makes me wonder, is the video framebuffer fixed to bank A, even if bank A is empty (desoldered)? Would this also mean that a IIci can boot with RAM in bank B only, but would show a black picture? If anyone could test that, that would be great.

Also, would it be possible to force bank B to be bank A (if that didn't happen already), or does that require a ton of rewiring? There's a lot of lifted pads for the onboard RAM + bus transceivers, so I'm not going to bother trying to refit that stuff.
Posted by: Phipli on 2023-07-03 07:21:28
This makes me wonder, is the video framebuffer fixed to bank A, even if bank A is empty (desoldered)? Would this also mean that a IIci can boot with RAM in bank B only, but would show a black picture? If anyone could test that, that would be great.
Video is physically wired into bank A, it won't give built in video without bank A.
Posted by: 8bitbubsy on 2023-07-03 07:23:37
Oh well, scrap board then I guess.
Posted by: Phipli on 2023-07-03 07:36:36
Oh well, scrap board then I guess.
How come? Are the ram pads also mangled?

You could use a video card?
Posted by: 8bitbubsy on 2023-07-03 07:42:44
Yes, a lot of broken pads. Anyway, I already went ahead and forcefully scrapped components from the board.
Took the SWIM out, in case it's possible to manually re-wire it to a DIP28 socket so that I can use it in my Macintosh SE (together with FDHD ROMs).

I'm not sure if it would be compatible, would have to ask someone that knows.
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