Hi Ronald that also sounds like a sound rom error, could be capacitors breaking down

I had pretty much the same issue on a STTNG board (also DCS). Ironically, during debug I put my WCS sound ROMs in it and it sounded identical to your recording.

I chased many ghosts, including replacing the DSP and associated RAM. Ultimately, I found that the issue was a flaky contact on the socket for PAL used for decoding. I think the PAL was at U16 on the DCS board. There must have been flaky chip enables causing bus contention, leading to the static. I never saw it on my scope, but replacing the socket ultimately cured the issue.

The weird thing is that all of the built in tests would pass. This was a pain to debug. High-ish clock frequencies, bidirectional floating bus, and different bus widths depending on access type. I wish you luck!

That must be C52, 100uF 16V. Looks like it has been spitting electrolyte for quite some while, seen by the legs of L1

C52 DCS (resized).jpg

It is a filter capacitor for the 5Volt.
With C52 removed, the board would most likely work but maybe with a little hum or noise.
If so, replace it with a 100uF 25V

RonaldRayGun did u manage to solve this? I'm having a very similar issue.
Thanks!

U sure that these are on the DCS board, not the pre-DCS? Still, i suppose the message is the same: change all the caps.. hmmm
Well I am still testing continueties etc, but I have soon checked pretty much every trace and all seems fine.
Next step would be to change the caps I suppose..

Please tell me more on how to test J6 (Aux out)? Is it simply a matter of tapping in speaker cables and connecting a speaker on the other end? Should something go between, like a capacitor or resistor?

So an update: i checked ALL caps with an ESR meter and compared to a working board. I replaced some suspected ones, in total I have replaced:
C32, C41, C50, C52, C15, C22.
And I cut C37, C45 without replacing these, because pinwiki says so.

I also checked continuty on most places, all resistors, all diodes, and diode tested the roms - didnt find anything.

So I plugged it in - still same problem!

Removed audio board again and resoldered some joints that visually looked like cold solder joints, but they where measuring fine.
Also noticed that one leg on C52 (that was replaced) was a little loose (but continuty was tested fine anyway), resoldered that as well.

Now, sound is still disorted but only at the first 2-3 minutes when firing up machine from cold state, after that the sound becomes perfect!!!!

If powering off and then on, sound will still be working fine.

Actually, that is how the problem was noticed from the beginning, it was showing the same symptoms as now (sound disorted when board is cold), then it went to always be disorted, regardless if warmed up.

Now I am left with the following options:
- live with it
- change C20/C21 (the 2 big caps), eventhough they are measuring fine with the ESR meter
- troubleshoot further by measuring voltages on different places on the board and comparing to the working board. I would need some hints on what to measure.

I am thinking of mesuring voltage direct after the c20/c21 big caps, and see if the voltage is increasing by time. That would indicate bad caps (c20/c21) and also explain what I am experiencing that the sound gets better after a while.

Am I thinking correct in my troubleshooting? Is it AC voltage I should be measuring after the caps?

I did not check aux out since it seems too complicated/time consuming to me, but will do it when I have no ideas left

Today I measured some voltages and noticed that the +5v line that comes from J3 seems to be where I should dig into. I measured it at C79.
It measures 4.84 VDC when started from cold state, and slowy increase until it reaches 4.91 VDC within a minute or two, and 4.93 VDC if waiting longer.

Compared with another working machine, I got 4.91 VDC at C79 right away!

This must mean that a cap is making this? C50-C79 are the ones involved according to schematics, i think.

Another increasing voltage is at C11, there I got 4.88 VDC at cold start, but it increases to 5.0VDC within 30 seconds, which makes me beleive that my issue isn't there (since it takes more than 30 seconds for the audio to become good).

Did you clean up the electrolyte? That can eat away at pins/traces.

BTW, regarding your avatar -- that episode was on Futurama last night.

I measured DC on C79. That should be correct, right?
Just tried to measure AC, with one lead at each end of C79, but showed 0. I am pretty sure it should be DC.

Actually, here is images showing 2 things that I am measuring:
1. The +5 VDC line, as stated above (2nd image)
2. The voltage after the C20/C21 caps (1st image). Easiest to measure at C18/C19 or at C10/C11. Really I think even this is DC and not AC, because the AC signal is tranfered to DC at the rectifier diodes D1-D4 = before the caps. Am I right?

20210417_192605 (resized).jpg20210417_192644 (resized).jpg

Well thank u, I suppose u mean C18 & C19, not C29?
I also am a bit afraid to remove the big caps, to not damage traces.
Do/could C20/C21 has any effect on the voltage on C79?
If yes, then I def.wiill change them as next step. If no, I think my issue lies somewhere else?

4.84 volts is fine. 5.00 vdc is even better. TTL is spec. to work between 4.75 & 5.25 vdc.

You can measure the AC component or ripple before the regulators. It should be small, less than 40 or 50 mv. You will always have a tiny bit of ripple or noise from a full wave bridge. It may not be the source of your distorted audio.

Thanks, I'll measure that right away!
If I understand u right, I should measure AC voltage on C79 (red lead on positive, black on the other end ie ground) and that should not exceed 40-50 mv?
I did not measure that accurate before, will do it again.

Remember C79 is just 5v, if you want to check -5vdc you need to check it on a different location. I'm not sure if your sound board uses - 5vdc.

U guys are great, thos forum is great!
So just a quick update on some measurements I made. Regarding the ripple voltages, these should be considered unreliable since even when the DMM probes weren´t touching anything, it showed 20-60 mVAC on the DMM.

C10: -4.92 VDC
C11: 4.99 VDC
C18: 16.15 VDC, ripple: 70 mVAC
C19: -16.30 VDC, ripple: 70 mVAC
C79: 4.83 VDC (increasing with time), ripple: 80 mVAC (how is it possible that AC is present on this line?)

Compared to a working board, ripple voltages on C18/C19 are the same. Only diffrence is that C18 is 16.30 VDC on the working board, and C79 is stable and not increasing with time. I don´t know if this made me any smarter, because the measurements seems OK?

From here I think I give up on further measurements and just go ahead and replace the remaining caps C18, C19, C20, C21.

Stay tuned

So, replaced the remaining caps (including the 2 large ones) but problem is the same.
Time to throw in the towel?

I don't think your problem only comes from the capacitors.. Did you properly clean the board and all the affected ICs of the corrosion ? Changing the 10k resistor at too, cleaning the board to make sure the corrosion wont cause more damage in the long run? Even the ribbon connector's header has good chances of having corrosion. It only takes 1 of these connections to be bad to cause the data to be garbage and the ADC at u20 to output noise. I have circled in red all the pins that I could easily identify has having corrosion on them. Not sure how much of all this you cleaned, but I boxed a zone in yellow where for the best long term solution all these parts should be removed, the board cleaned , cleaning the IC's pins as well, installing sockets. Corrosion can and will slowly creep up and pins and make their way inside the part breaking it. The good news all the ICs , seem to be good, u16 probably being the hardest part to find and also the likely culprit here, but since after a while it starts working because the bad connection(s) finally manage to carry over the signal so that the whole logic system can work. As the 5v rises in your machine because slowly more power is allowed to pass by by the thermistor, feeding the transformer , feeding the regulators, it also means the voltage at which those pins are also increased a bit, allowing it to work even with the corrosion. Then if you turn off the machine and turn it back on , the thermistor hasn't cooled yet so it still allows full power to go through the machine , hence the 5v is already near 5 volts. You compared voltage with another working machine , was it another WCS ? A lot of things could explain why the other machine starts at 4.91v from cold start, and not yours. The initial temperature of the thermistor, the model , is there one or was it removed, the transformer winding , the AC voltage in the wall . The goal is to minimize the initial current rush from turning on the machine. It could also mean in your case that the sound board , or any other board is pulling a bit more current than that one you compared with, which also goes along the lines of corrosion. Corrosion changes resistance of things , which changes the current that goes through. It's indirectly related , but how does your CPU board look like ? Is there any battery acid damage on it ? You should also change the ribbon cable since you can't tell if corrosion went up the pins and inside the connector.

I know it sounds like a lot , but in parts the cost isn't really big. In time a little more, but if you plan on keeping this machine alive for another 20-30 years, you'll spend what it deserves.

1c72172430019cdf43258d653488462578ae5ca5.jpg

Did you ever replace the socket on U16 like I mentioned in post #5 in this thread? Looks like there is clear evidence of electrolyte under the socket, so there is a good chance that it has seeped into the contacts there.

It seems you have tried most of the common things. Why not just send the board out for repair?

$100~150 starts to sound pretty cheap for a repair when you have probably spent half that already in parts and certainly FAR more than that in time.

I think I have a very similar issue to you. Just moved my games and have lots of static and distortion from the speakers but only when playing a sound. I confirmed the sound board was the issue as the problem also occurs in Demolition Man when I swap the board and ROMs.

Did you ever resolve this?

Were the large capacitors recently replaced? I’ve seen a lot of boards where the through hole plating was ripped out causing an open. Ran into another board missing one of the voltages causing audio issues.

I've only replaced the 1uf electrolytic caps. Solder on the 10k uf caps is intact. In fact all the solder joints look good. No leaking caps on this board either.