Trying to get a System 4 CPU to boot. Anyone have a spare System 3 or 4 CPU board that boots that they would be willing to part with? Thinking it will be easier to analyze side by side and/or part swap.
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Trying to get a System 4 CPU to boot. Anyone have a spare System 3 or 4 CPU board that boots that they would be willing to part with? Thinking it will be easier to analyze side by side and/or part swap.
Quoted from pincoder:Have you tried these test ROMs?
https://pincoder.ca
You should be able to get things running there without the need of another board..
I'm running test ROMs and the CPU isn't starting. Reset circuit is only hitting 4V and clock generator wave looks a bit saw-toothy. Processor tested good (popped it into another game). Want to scope out a working board to get a better idea of how everything should measure out. In any case, have a couple of components I'm waiting on from digikey that I hope improves the situation.
Quoted from pincoder:Interesting. Sounds safe to assume you've already tested the obvious.. 5V and 12V power. Keep us posted
Yep, bench testing with switcher--5.2VDC at 6800 Vcc. Reset starts low and snaps up to and stays at 4VDC. I found a 2N4403 that looks to be bad in reset circuit but didn't have any on hand. On my scope while inspecting address lines it seems to bounce very rapidly eg from fixed high to momentary waveforms so my theory is it's randomly resetting as reset isn't quite high enough. That said, I tried forcing pin 40 to +5VDC and it still seemed to be noisy on address lines...So wondering if clock isn't clean enough? I pulled RAM and PIA chips just in case but no change.
I grabbed a battery damaged System 3 CPU board off of eBay for cheap--figured worst case can harvest clock generator ic if necessary. But hoping CPU will come up so I can cross compare the two boards.
Quoted from pincoder:Ive seen the clock waveforms on a good board and I have to say they don't look very clean. If I get some time this weekend I'll send you a pic.
Thanks! Here's what I measured:
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