arnold.exe
New member
I'm not any kind of expert on this, so bear with me if I'm asking something completely bonkers. I have this extra Macintosh Classic logic board, that I managed to raise from the dead after a recap, a couple of washes, some reflowing, reseating, and so on. I should be content with having a spare for if or when the other board I have in my Classic has some sort of fault. But I was thinking about how the SWIM/BBU have this 15.3MHz crystal for driving the peculiar CRTs that were used in these, and reading the documents here https://archive.org/details/SWIMDesignDocs, specifically the SWIM Chip User's Reference, that it's essentially an extended IWM from the Apple II days.
The IWM chip in that machine of course used a 14.318MHz cyrstal, being intended for use with a NTSC display (and I assume a different crystal for our PAL pals). Could I just....swap the crystal for a 14.318MHz one and get something like CGA compatible video signals out of this board? I assume voltage levels would have to be corrected, buffers added, and so on, but the core syncs would at least be correct. I would hazard a guess the floppy drive would function strangely, and probably the sound too, being part of the same chip. And of course, without an analog board, I would have to power the works with a different supply, but I happen to have a Mean Well that can output +12/-12/+5 from a failed venture into building modular synthesizer boards by hand.
This is absolutely too ambitious for me and the projects I do, but I'm genuinely curious if this kind of hack could work and be useful to anyone else if it did. I think it would at least be reversible, being a simple through-hold soldering swap.
The IWM chip in that machine of course used a 14.318MHz cyrstal, being intended for use with a NTSC display (and I assume a different crystal for our PAL pals). Could I just....swap the crystal for a 14.318MHz one and get something like CGA compatible video signals out of this board? I assume voltage levels would have to be corrected, buffers added, and so on, but the core syncs would at least be correct. I would hazard a guess the floppy drive would function strangely, and probably the sound too, being part of the same chip. And of course, without an analog board, I would have to power the works with a different supply, but I happen to have a Mean Well that can output +12/-12/+5 from a failed venture into building modular synthesizer boards by hand.
This is absolutely too ambitious for me and the projects I do, but I'm genuinely curious if this kind of hack could work and be useful to anyone else if it did. I think it would at least be reversible, being a simple through-hold soldering swap.