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CPS 1 audio randomly disappears (FIXED/SOLVED)

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Hi guys. :)

In the same week I received two pcbs, Street Fighter II CE and Captain Commando, both originals and with the same bizarre issue.

The games work normally but suddenly ALL the audio disappears, but if I turn them off then on again the audio comes back until it disappears again. I left the SFIICE turned on for a fair amount of time and the issue mysteriously stopped happening, but it still happens with Captain Commando and I'm left with the question: WHAT COULD BE HAPPENING TO CAUSE SUCH AN ISSUE???????????? 6116 ram, Z80, ym synth, 3014B??? The audio PRG is ok so what's happening???

Any help would be appreciated and I know others do have these kinds of issues. :(

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Is the amp chip getting very hot? Sounds like thermal protection may be kicking in. Cause can be bad caps, or a very noisy 12v supply.


Also check for bad connections at the Jamma connector, it's unlikely both boards would have the same fault? Something common to both is more likely, cab wiring, PSU, interference.

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Yes, I've been thinking about it with Captain Commando but the SFIICE makes strange noises after the audio goes out. It's not a noise of something trying to make contact again when the audio would be still playing but interrupted of reaching the amp, but sounds more like quick pieces of garbled audio, as if the........ YM synthesizer(?) didn't know exactly what to play.
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Hiiiii, Womble.

I'll reproduce the fault again (I know this will happen again :x) and will check if it gets really hot.

Very noisy PS? Would I need an oscilloscope to check it?

The JAMMA connector is pretty clean and shiny.

I use all my PCBs with my super gun and to generate the audio line level signal I use audio transformers with the right calculations not to stress or damage power amps.

It only happens with these two last boards I've just bought. The audio of all my other pcbs just work flawlessly, including 9 other CPS1 pcbs, between dash and 10Mhz versions.

But, how can I check my PSU without an oscilloscope? I use an arcade PSU Eago, 15A in the 5 volts line, 2,5A on the 12V and 1A on the -5V. Power is regulated on 5.05V.

interference? Would be some sort of signal flowing through the 12V in case of any issue with the amp, or in the 5V line if it's a logic issue?

What worries me is that these kinds of issues are becoming more common. It's the first time it happens to me, in my case in a double dose, but I heard the exact story from others.

Thanks a lot...


- - - Updated - - -

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I took the time to analyze logic states around the audio section and at the moment I got the following:

When audio is on, there are lots of activity in every pin possible, with good healthy pulses.

But when audio goes out, all address lines and I/O pins become floating. No activity at all. Same happens with the YM2151 and audio ram (2015, 2018, 6116...).

I started by removing the Z80 and installing a socket in place. I seated other Z80, this time the correct one, a Z80A, but no success. After a while the issue happened the same way.

Later, I decided to replace the audio ram don't believing this could make any difference, but I tried. installed a 6116 in place of the original 2015 and ...... no change.

Analyzed the pins of eprom 9 (audio PRG) and found that when the audio goes out, address inputs get stuck high for the most part. A5, A4 and A3 get stuck low (pins 5,6 and 7). All outputs get FLOATING and the control pins, CE(-) and OE(-) get stuck high. This explains why we have no outputs.

According to the schematics, the eprom 9 CE pin comes from the pin 12 from SOU1 PAL through CN1, pin B4. So I programmed a GAL16V8 with the corresponding .JED, but no change.

Z80 reset line is OK. Clock line is OK.

The biggest hassle is that I'm working on the smaller pcb that's full of unreachable smds:x

I would really like to replace one 74ls138 as it does the CS(-) functions for both OKI and YM2151 chips.......... And I have no sound at all...

And a pair of 74ls374 also controlled by the above mentioned 74ls138, that seem to receive pulses from the 68k and then sends them to the sound eprom's address inputs. They are fed by a clock pulse that comes from another PAL, the IOA1 that passes through a 74ls32 at region 5B, with outputs at pins 6 (sound 1B) and 8(sound 0B). I imagine that without this clock pulse, no audio at all!

Also a 74sl74 that seems to control the SOU1 pal and the select pin from the OKI, but it seems a bit out of question...

These are the suspects at the time. The reason I didn't probe them yet is due to the fact they aren't accessible when the b board is connected since they are smds.

Comment people!

Our beloved hardware, marvelous piece of past is getting older and older. I'm tired of seeing dead or partially working A boards with almost no hope of fixing. I ask it with passion. Let's try to fix them!





In case someone is interested, I have the schematics for the CPS1 A and B boards.

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Problem solved!

Last Sunday I've fixed both boards.

The first suspect for me it was the audio circuit clock, but I analyzed it in two situations only: When the audio was ON and when the audio was already OFF.

This small mistake led me to replace the Z80, the audio ram and to program new GALS as substitutes for the SOU1 and IOA1 PALS unnecessarily. Despite the fact they could be related to the fault, nothing changed after replacements. I tried to fix first the Captain Commando, since the SFIICE had the same issue.

So I imagined a third situation: The possibility of a clock signal random inconsistency...

I placed the logic probe's tip on the 3,579545 MHz oscillator's clock pin and then powered up the board. I kept holding the tip on that pin for about 7 long minutes watching healthy pulsing lights and listening to the game's normal sounds until...... All sounds gone away and the clock pin got stuck LOW for about one second long and started pulsing again, but it was too late. Everyone involved in the sound system got lost and didn't know what to do next...

Replaced the 3,57MHz oscillator and the sound issue was gone.

I did the same with the Street Fighter IICE A board that came with the same issue without even testing and ...... Problem solved too.

Double victory!

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CPS 1 audio randomly disappears (FIXED/SOLVED)


How weird, crystals usually die completely if at all and for 2 to have exactly that same issue is crazy unusual


I have a Final Fight board that did something similar - sound would work normally for a while but then it would just freeze, the game would run normally and the sound would make a single tone consistently (which gets very annoying very quickly)


I restarted it and usually it fixed it, then one night it froze and didn't come back on a restart. I socketed and replaced the Z80 (with the proper Z80A like you did) and that seems to have solved it



Sent from my iPhone using Tapatalk

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Do you know one thing? I started trying to repair one of them, since they had the same problem. I replaced too the original Z80 for a new Z80A on the Captain Commando pcb, but on the SFIICE I left the original Z80 there and replaced only the oscillator. Only the oscillator replacement fixed both boards. Friend, when I say it was bizarre to get two boards the same day with the saaaaame problem, and from different sellers, you don't believe me.... Take a look at the xtal you removed from your Final Fight, if you still have it. I'm now looking at both faulty ones I've removed and they have the following writing on them: VX-8111 / 3.579545 MHz(obvious) / JVC / 1E (one), 1F (the other one). The two bad osc are of the same brand. 1E and 1F sounds like date of manufacturing or something the like.

Pay attention if you are having sound problems with CPS1 A boards. Before replacing Z80, rams or something with more legs, look at the osc. If it's exactly the same part I described, take the time to analyse if its pulses fail. In fact, an active osc is nothing more than a reduced version of a real size osc composed of a Xtal + 2 gates of an inverter + 2 or 3 small ceramic caps + 2 or 3 resistors inside a shielded cage. An intermittent fail in one of the gates of the inverter is probably the cause of the pulse getting stuck sometimes. It is sufficient to crash the audio subsystem.

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  • 1 year later...

A few years ago, I had the same issues (sound works at power on, then vanish at a random time, and came back only on turning it off/on) with 2 a-board (both from different seller, one from willow and the other captain commando) and I fixed it by changing the osc.

Both A boards are the short ones.

Not an uncommon issue after all

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  • 3 years later...

I have a cps1 (a+b+c) street fighter champion edition that has sound problems on board A (cps1 with sound problem, effects, kicks, punches and missing voices). I've already done the replacement of the 6295 oki as shown in the figure. and the problem remains. can someone help me solve the audio problem?  the soundtracks are working.  help please

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On the A-P forums you said the sounds come back when you touch the capacitor in the sound section. If that is the case, simply reflow or replace the cap and you should be fixed. 

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  • 3 weeks later...

Theres a few simple things to check.

Check what the 12volts is doing at the board, bad connections at the edge connector may make the 12v come and go, the only thing that uses the 12V is the audio amplifier, so a 12v feed that is intermittent will make the audio vanish, and it will be very sensitive to touch.

Check the solder joints under the large amplifier chip on the heatsink, cracked joints there can make things come and go.

Also does the heatsink get very hot? 

Edited by Womble
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finally after a lot of work i discovered the defect in the audio that was causing problems in the sound of kicks, voices etc. after changing oki chip, z80, all capacitors, 4 ci 5218a, ci yamaha ym2151, chip ym3012 among others, I found that the defect was simply resistor R47 (2.2k). problem solved and sound working perfectly.

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