The story so far. Many years ago, when I was young and foolish I picked up a CPS1 32-in-1 board from China. It frankly worked really well for quite some time. But recently it started to have audio issues (thinking it's the z80). I pulled it apart, and found a large number of questionable repairs, but nothing that looked too out of place. It was a 10mhz board that had been upgraded to 12mhz by having the crystal swapped, most of the capacitors had been replaced (poorly and not sure with new capacitors) and there's a weird diode replacement job (see pic). I also had a clean SF2 WW board set, so my thoughts were to use it as a diagnostics platform. When I connect the board, it boots and runs (with audio thus showing the audio issues were on the old A board and not the B+C multiboard). But with heavy graphics corruption. I thought that
MIGHT be related to the 10mhz crystal, but after
swapping those I'm still seeing the same issues. I did confirm that the pin shown here earlier does reset the board. So that's one mystery down.
Really not sure what the deal is. What other than the crystal could have been changed out that would cause graphics issues if it were missing?
(diode weirdness - and note that the crystal shown here has no markings so can't be sure it wasn't replaced)
Edit: Chip is a rebranded
YM2151. Diode is running to pin 22 which is +5v (vdd). So while weird looking, it seems to be right.
Edit: Thinking about it, the sound issues may be because of a faulty crystal on the z80. So that blank one may be the issue. Guess I just need to find a 3.579545mhz full can crystal to test that theory with.
One thing I have now noticed, is that the CPU on the old board (Chinese bodge job with failing audio) has a 12mhz 6800 in addition to the 12mhz crystal.