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Repair Log: CPS1 No Sound

Agreed that it seems to be a digital issue. Something is making the Z80 crash although it’s intermittent. Have you tried different sound EPROMs? Maybe one of them is flaky.
I doubt it's the sound roms, although I could re-burn to test. Reason being: When I swap to a 100% known working A board with this game, zero issues. If I swap this faulty A board onto another CPS1 (converted SFII to Ghouls and Ghosts) I can re-produce these intermittent sound issues. This is why I'm focusing on the A board as the culprit.

I did just get in 4 extension cables for the connectors so that I can get underneath to probe the A board while it's on. I couldn't before from underneath and some of the chips are surface mounted.

Any suggestions on what to probe first?

Del
 
You're in a tough spot for diagnosis where your sound cutout is intermittent - you'd have be probing the right spot exactly when the sound cuts out.

Just curious - when you tested the 100% working A board, did you leave it running for an hour? If you did and the sound didn't cut out then I agree that we can narrow our focus to just the A Board.

This diagram is pulled from the PCB Junkie website:
https://pcbjunkie.net/index.php/guides/capcom-cps-cps-1-repair-guide/
cps1a-ic-function-smlr.jpg

Rather than logic probing, I suggest getting some freeze spray and hitting each chip that's involved with sound in the lower middle of the A Board with the spray one at a time. If you're lucky, the blast of cold will cause the faulty chip to glitch and you'll know your culprit.

One more thing - make sure your board is getting a steady 5.0V . Some boards are more tolerant of low voltage than others.
 
Had the same issue on 2 mobos in the past, and solved it by replacing the sound oscillator.
Ah, the sound clock crystal. Gotcha. Don't think I have that on hand. I need to order a few.

Edit: Wondering if this is a suitable replacement or not: https://www.digikey.com/en/products/detail/ecs-inc/ECS-100AX-035/827253

Edit 2: Going to link this here too with a similar issue where the clock/oscillator part fixed it: https://www.aussiearcade.com/topic/75949-cps-1-audio-randomly-disappears-fixedsolved/

Del
 
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Whelp. I fixed it! It was indeed the sound oscillator/crystal. I used a known working one from a donor board.

Check out how rusted/corroded it was underneath:
1000015393.jpg


I also got those extender cables in and work great:
1000015395.jpg


Now I'm going to move on and start a thread on another CPS 1 PCB that has graphical glitches. I've also narrowed that one down to the A board. Go figure...

Thanks again for everyone's input!

Del
 

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I'll also write about the sound, maybe you can help. I bought a Street Fighter 2 CE kit on aliexpress. Upon arrival, it turned out that it was CPS 1.5 with the audio part transplanted from the donor cps 1.0. The sound worked fine at first, but disappeared after 10 minutes. If you let the board rest for 30 minutes, the sound appeared. Then it stopped helping - now, when the power is turned on, random sound or music is played and then the game is silent. That is, there is a problem with the digital part. I soldered all the legs of the chips, tried to change the power sources, another B + C board, checked the quartz frequency - 3.57mhz and it comes to the right leg of the z80. The only problem is with the sound, there are no artifacts in the games and the controls are working.
 
Sound cutting out after 10 minutes and coming back after the board rests sounds like the amplifier overheating. It should have a heatsink on it - if not, add one.

Now that you’re not getting anything but random sounds … that could be a code issue with the Z80. Dump the EPROMs for sound and make sure the checksum matches MAME. It should be the ROMs label 9, 18 and 19.

IMG_4397.jpeg
 
I connect the board to the TV, the volume is not high and the amplifier does not heat up at all. The original radiator is on it. It's not a B board- I have 87 in 1, and I ran the same SF2 CE from it in different regions, as well as other games - the behavior is the same. There is a random sound or music at the start and then silence. In this topic, I read about shorting the 26 and 29 pins of the Z80 to reboot it - if you do this, the same sound is played as when the board is turned on.
As I understand it, the problem is either in the z80, 68000, or sound ram. I hope it's not Motorola. I'll be looking for a 4mhz z80, but what can I replace the sound ram with?
 
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I connect the board to the TV, the volume is not high and the amplifier does not heat up at all. The original radiator is on it. It's not a B board- I have 87 in 1, and I ran the same SF2 CE from it in different regions, as well as other games - the behavior is the same. There is a random sound or music at the start and then silence. In this topic, I read about shorting the 26 and 29 pins of the Z80 to reboot it - if you do this, the same sound is played as when the board is turned on.
As I understand it, the problem is either in the z80, 68000, or sound ram. I hope it's not Motorola. I'll be looking for a 4mhz z80, but what can I replace the sound ram with?
I'm not quite understanding what hardware you have. Can you post pics to better describe it?
 
CPS1.5 with poppulated audio part from donor board. But not all parts -Z80 has a 6 Mhz model installed.
 

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Only one capacitor is missing, and it's in the analog part of the amplifier harness, but the problem is with the digital part.
 
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