General Category > LisaList2
Lisa Video, ProFile power issue, NiCad Leak fixes, etc.
AlexTheCat123:
I see what you're saying now. I just checked A1-A10 at the inputs to the muxes and five of them (A5, A7, A8, A9, and A10) are stuck either high or low, which doesn't seem normal, so you were probably right about the problem being on the CPU board after all. Now it's just a matter of figuring out what exactly the problem is.
Edit: It actually looks like those five address lines have activity up until the Lisa starts testing the I/O board. They only get stuck after the I/O board test begins.
rayarachelian:
--- Quote from: AlexTheCat123 on May 29, 2021, 12:56:28 pm ---Edit: It actually looks like those five address lines have activity up until the Lisa starts testing the I/O board. They only get stuck after the I/O board test begins.
--- End quote ---
:( that is truly bizarre, is there something on the I/O board doing that? I don't see how anything other than the CPU should be able to set the address lines, and why would they lock?
Do you have a spare CPU (not board) to swap out with?
I can understand the CPU hitting addresses 00fcxxxx as it touches I/O space, but it should also go back and forth with the ROM which is at 00fexxxx and lower RAM - at least where the video display page is, which should be the highest 32K of the physical RAM, so those lines should be bouncing around, not fixed.
AlexTheCat123:
I have two spare known-good CPUs and they both do the exact same thing as this one. I also have a spare CPU board, but something's wrong with it and there isn't any activity on the CPU's address or data buses. This is a really weird problem! Maybe the CPU's getting stuck in some sort of a loop as a result of not being able to read the contents of the shared floppy RAM?
rayarachelian:
There is a STOP opcode, but it's unlikely to be invoked. Generally it's used to sit in an idle state until an interrupt happens.
Even if things so south, generally in the Lisa Boot ROM, you should still be able to use the mouse and keyboard, and so the CPU should still function and the address lines shouldn't be locked down, even then, it should switch between reading from the boot ROM, accessing RAM, COPS, VIA, etc.
AlexTheCat123:
Both the mouse and keyboard are inoperative for me. I don't know if it's a COPS error (unlikely, since it has been replaced with a brand new and freshly assembled X/COPS) or if it's something related to the strange address line behavior. I hope that the replacement 6504 and I/O board ROM that I ordered will free up that stuck MA8 line and maybe get everything working again, but I'm not too confident about that. The 6504 does get pretty hot, so maybe something is wrong with it.
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