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Repair Log: CPS1 No Sound

ShootTheCore

ShootTheCore

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Also documented with a demonstration video at https://shootthecore.tech/repair/repair-capcom-cps1/

I didn't take as many pictures of this repair as I should have - sorry about that!

In for repair was a CPS1 main board with no sound.

First, I tested the B + C board on another CPS1 main board. The sound worked fine there, so the sound issue wasn't from a bad ROM or problem with the ROM board.

Next, I probed the OpAmp and final amp with an audio probe. I wasn't able to pick up any audio with the probe, so amplification wasn't the problem.

Next, I probed the Z80 Sound CPU's lines with my oscilloscope. I confirmed that the Z80 was receiving Power, Ground, a Clock signal, and that Reset was getting triggered at power up. All of those signals checked out, but the Z80 seemed to run for a second and then halt.
IMG_7597.jpg

I probed all the Address and Data lines between the Z80 and the edge connector for the ROM board - they all checked out. I suspected that the Z80s RAM was bad - that would cause the Z80 to start program execution but then crash. I desoldered the RAM from the board, but it tested fine out of circuit in my memory tester. I installed a socket and then reinstalled the same RAM chip.
IMG_7598.jpg

Next, I desoldered the Z80 CPU itself from the board, installed a socket, and tried another Z80 CPU. That was the problem - the sound started working properly with the other Z80.
IMG_7605.jpgIMG_7606.jpg
IMG_7608.jpg

An excellent resource for starting out on any CPS1 repair is this writeup by PCBJunkie:
https://pcbjunkie.net/index.php/guides/capcom-cps-cps-1-repair-guide/

His photo of all of the chip functionality labeled is fantastic - hopefully he won't mind me sharing it here.
cps1a-ic-function-smlr.jpg
 
You’ll notice the silkscreen says Z80-A but the part was a regular z80. Z80 runs at 2.5mhz. Z80a is 4mhz. The clock here? 3.5mhz. They cheaped out and run it over-clocked so this is a common failure. Replace with a z80a for longevity!
 
ekorz said:
You’ll notice the silkscreen says Z80-A but the part was a regular z80. Z80 runs at 2.5mhz. Z80a is 4mhz. The clock here? 3.5mhz. They cheaped out and run it over-clocked so this is a common failure. Replace with a z80a for longevity!
Click to expand...

That's actually a Z80A. The A simply means it's tested and will run at 4MHz. The part number is Z0840004PSC that last 4 is the speed rating. You'll see some with 6 and 8 as well for 6MHz and 8MHz speed ratings.

Don't feel bad, I thought the same for a while until I looked up the data sheets. :)
 
channelmaniac said:
That's actually a Z80A. The A simply means it's tested and will run at 4MHz. The part number is Z0840004PSC that last 4 is the speed rating. You'll see some with 6 and 8 as well for 6MHz and 8MHz speed ratings.

Don't feel bad, I thought the same for a while until I looked up the data sheets. :)
Click to expand...

I never feel bad about learning something. Thanks! That does mean that now wonder why they fail so often then - the overclocking made for a great explanation.
 
Good job there!

So even after probing the Z80, the RAM was still suspected to be at fault? It goes to show...

I need to repair a board which plays sound fine on boot but plays random SFX and music. I don't have the skills to probe the board so will change the Z80 for a Z80a.
 
samlieu said:
I need to repair a board which plays sound fine on boot but plays random SFX and music. I don't have the skills to probe the board so will change the Z80 for a Z80a.
Click to expand...
Check connections between the A and B board near the Z80. If it can't connect properly to the sound ROM and the 2 SFX ROMs on the B board you'll have issues. Also check the sockets and those 3 ROMs for corrosion. Clean the legs of the ROMs if needed.
 
Great resource here! Was going to post something similar to the issue I am having but going to do more homework first!

Del
 
Whelp, replaced my sound CPU and no change. Going to try the sound CPU ram next, as I have a donor PCB I can grab it from.

No harm done. I'm pretty adept at socketing iC chips.

My symptoms from the start: Intermittent sound. SF II game will start up just fine and will randomly lose sound. At times turns to screeching and/or silence. Game reset restores the sound. Has nothing to do with overheating or cold solder joints apparently.

Confirmed it's an A board issue. I have a 100% working A board I swapped in from my UN Squadron game and it works great for hours. Swapped this one to another game and audio issue persists. A board issue indeed!

Del
 

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More progress. Replaced the Sound CPU Ram with a known working one. Thought I had it solved after running the game for an hour in attract mode and then playing for another 15 minutes. Left it in attract mode afterwards, and the issue is back. :-/

Tried replacing the HA13001 sound amp. Nope. Same issue.

So I'm back to the drawing board. Intermittent issues are always hard to chase down. Maybe the Op Amps?

Del
 

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When the sound stops working, does it stay dead until you power cycle the board? Or does the sound come and go?
 
ShootTheCore said:
When the sound stops working, does it stay dead until you power cycle the board? Or does the sound come and go?
Click to expand...
Stays dead. Sometimes I hear pop instead of sound or a screech. But mostly silence. Power cycling restores it.

Del
 
Interesting. Well, the problem is either with the digital side (Z80 crashing) or with the analog side (OpAmps or final amp failure, or capacitors).

If you have a multimeter or scope, probe Pin 4 of the YM3012 DAC. When there is no sound being generated, there should be a steady clock pulse. When sound is being generated, additional activity will appear on that pin as well.

If you don't get any activity besides the clock pulses on the DAC when the board stops playing sound then you know your problem is on the digital side.
If you do get activity besides the clock pulses on the DAC when the board stops playing sound then you know your problem is on the analog side.

@channelmaniac made a great video demonstrating this with the Neo Geo hardware here:
View: https://www.youtube.com/watch?v=__qTYNFvl3I
 
I need to give that a shot, but I'm pretty sure it's a digital issue. I tapped into the Z80 Sound CPU at the reset pin 26 and ground at 29. I soldered a wire on each pin. When I lost sound, I was able to jump the two wires together to send a reset to the Sound CPU and the sound came back. If I held the two wires together the sound reproduced what I am experiencing, where it would go completely silent until I let go. I experimented by holding the wires together until gameplay started then removed them. I was able to get silence, then the sound effects only would play (no music). The music trigger is sent at the beginning of the stage but after that it doesn't send it until the next round. Sound effects on the other hand sent triggers throughout the round. Was cool to play with it and learn.

So I let the PCB run and when it lost sound I'd trigger the reset on the Sound CPU. And music/sound effects were back. I was able to consistently reset the sound when I did this back to normal.
Z80A_Pinout.jpg
 
Also forgot to mention that I had a spare Yamaha DAC (YM3012) so I socketed and swapped another one in. Nothing changed.

I then proceeded to the Z80 reset as I mentioned in the post above.

Del
 
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.
 
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