(Topic ID: 280582)

Distorted Sound (WPC/DCS)

By RonaldRayGun

2 years ago


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There are 81 posts in this topic. You are on page 1 of 2.
#1 2 years ago

The sound on my WCS suddenly become very distorted (after moving the pin). There is only noise when a sound is played and not in between sounds (see link). Anyone knows what the problem is?

https://drive.google.com/file/d/1zxC2LYf4oH1b-SvcAAos_-sMOZa3j_lq/view?usp=sharing

#2 2 years ago

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

#3 2 years ago
Quoted from willowpuss:

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

Do you know which capacitors in particular that I should replace?

#4 2 years ago

Anyone have any idea what’s wrong?

#5 2 years ago
Quoted from RonaldRayGun:

Anyone have any idea what’s wrong?

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!

1 month later
#6 2 years ago

Is there an electrolyte leakage from C53? What is the role of this capacitor?

85A0936D-4BD5-4C46-AC28-231182BEFD49 (resized).jpeg
#7 2 years ago

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

#8 2 years ago
Quoted from zaza:

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

Thanks zaza. Yes you are right, it’s C52. Do you know what the purpose of this capacitor is?

#9 2 years ago

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

3 months later
#10 1 year ago

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

#11 1 year ago

ravve
So far I have only replaced C52. It didn’t solve the problem but needed to be done since it was leaking electrolyte.

Next I will reseat/replace socket at U16. If this doesn’t work then I will check aux out at J6 to see if it is distorted. This will determine if the problem is in the power amp circuit downstream or upstream in the pre-amp.

Please let me know what you find on your end and hopefully we can crack this together.

#12 1 year ago

Change all the Electro Caps

#13 1 year ago
Quoted from WH20_Buzz:

Change all the Electro Caps

Thanks. Which caps do you mean by electro caps?

#14 1 year ago

C36 & C37 .....C28 & C42....C35....C48 & C52 & C73....C18,C67,C68 and you are all done
Takes about 3 hours. I can do it a lot quicker..ha..ha

#15 1 year ago
Quoted from WH20_Buzz:

C36 & C37 .....C28 & C42....C35....C48 & C52 & C73....C18,C67,C68 and you are all done
Takes about 3 hours. I can do it a lot quicker..ha..ha

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..

#16 1 year ago
Quoted from RonaldRayGun:

ravve
Next I will reseat/replace socket at U16. If this doesn’t work then I will check aux out at J6 to see if it is distorted. This will determine if the problem is in the power amp circuit downstream or upstream in the pre-amp.

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?

#17 1 year ago
Quoted from ravve:

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?

J6 is before the power amp so I don’t think it can drive speakers. Just connect it with a 10uF cap, to block DC, to line/aux-in at your stereo, amplified pc speakers, or possibly small earphones and you should get sound.

#18 1 year ago

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.

#19 1 year ago

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?

#20 1 year ago
Quoted from ravve:

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?

If C20/C21 are bad then I guess that you would get a 50Hz hum in the speakers. Their purpose is to filter that out. Yes, you would see that as an AC voltage after the caps.

Did you check aux out? That would eliminate part of the circuit.

#21 1 year ago

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).

#22 1 year ago

Did you measure AC on C79?

#23 1 year ago
Quoted from RonaldRayGun:

ravve
So far I have only replaced C52. It didn’t solve the problem but needed to be done since it was leaking electrolyte.

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

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

#24 1 year ago
Quoted from RonaldRayGun:

Did you measure AC on C79?

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

#25 1 year ago

I kinda thought C20 & C21 were a no brainer to be the first Cabs off the Rank so to speak, so yeah they are the very first ones to change.
Replace C18 & C29 Tants and upscale those bad Boys to 50 Volts.

You will find all will be well after you change out the Big Boys C20 & C21.

The fact that the board is getting better the more Caps you replace is proof I what I keep going on about.
ALL the Electro Caps on ALL the Boards are now Farked after 30 years and they are now causing a lot of faults great & small

#26 1 year ago
Quoted from ravve:

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?
[quoted image][quoted image]

The purpose of all those caps is to filter out AC. So if any of the caps is bad you would get AC on the DC line. That’s why I asked if you have measured AC.

#27 1 year ago
Quoted from G-P-E:

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

What’s the best way to clean up electrolyte?

Quoted from G-P-E:

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

Sweet.

#28 1 year ago
Quoted from WH20_Buzz:

I kinda thought C20 & C21 were a no brainer to be the first Cabs off the Rank so to speak, so yeah they are the very first ones to change.
Replace C18 & C29 Tants and upscale those bad Boys to 50 Volts.
You will find all will be well after you change out the Big Boys C20 & C21.
The fact that the board is getting better the more Caps you replace is proof I what I keep going on about.
ALL the Electro Caps on ALL the Boards are now Farked after 30 years and they are now causing a lot of faults great & small

Thanks mate. I dread pulling C20/C21. One can easily rip the traces doing it. But I guess I have no choice.

#29 1 year ago

Melt the solder on one leg and gently pull the cap so it pulls the legs by about 1 mm..Then do the same for the other leg.
Do that 3 times and it will come out without damage. Dont keep iron on site for more than 5 seconds at a time and monitor the board heat

#30 1 year ago
Quoted from WH20_Buzz:

Replace C18 & C29 Tants and upscale those bad Boys to 50 Volts.
You will find all will be well after you change out the Big Boys C20 & C21.
The fact that the board is getting better the more Caps you replace is proof I what I keep going on about.

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?

#31 1 year ago
Quoted from ravve:

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 4.915.0VDC 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).

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

#32 1 year ago
Quoted from ravve:

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?

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.

#33 1 year ago
Quoted from Pinball_Postal:

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.

#34 1 year ago

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.

#35 1 year ago
Quoted from ravve:

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.

For AC it doesn't matter which way you put black and red leads, there's no polarity.

Quoted from Pinball_Postal:

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.

You're correct regarding C79.
Measuring over C18 and C19 would measure the +V/-V DC lines which feeds the regulators U25 and U26 which produces +5/-5 DC lines. These lines are used e.g. by the DAC U20. The +5 can be measured over C11 and the -5 can be measured over C10.

#36 1 year ago

This is a Push Pull Audio Amplifier and the output of the Bridge will be in the order of plus and minus 20 VDC with respect to Earth or Ground.
Any AC on these 20 Volt DC Rails WILL be amplified

The first Picture is the Audio Visual Board or WPC 95 the other 2 Pictures relate to the WPC 89 Audio Only Board

C20 & C21 10K uf 35 Volts on the WPC 95 Audio Visual Board
C24 & C25 4.7 uf 35 Volts on the WPC 89 Audio only Board

WPC 95 (resized).jpg

WPC89 Sound (resized).jpg
Whats WOT (resized).jpg

#37 1 year ago
Quoted from WH20_Buzz:

This is a Push Pull Audio Amplifier and the output of the Bridge will be in the order of plus and minus 20 VDC with respect to Earth or Ground.
Any AC on these 20 Volt DC Rails WILL be amplified
The first Picture is the Audio Visual Board or WPC 95 the other 2 Pictures relate to the WPC 89 Audio Only Board
C20 & C21 10K uf 35 Volts on the WPC 95 Audio Visual Board
C24 & C25 4.7 uf 35 Volts on the WPC 89 Audio only Board

Thanks mate. This is very helpful.

#38 1 year ago

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

3 weeks later
#39 1 year ago

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

#40 1 year ago

Time to change the 5 volt regulator and check and or replace any Caps hanging off it

#41 1 year ago

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
#42 1 year ago

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.

#43 1 year ago
Quoted from Pwedge:

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.

No I only reseated U16 but didn’t improve. I will replace the socket.

#44 1 year ago

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.

2 months later
#45 1 year ago

This is what I have done so far:

- Replaced 100uF cap C52
- Replaced 0.1uF caps C10, C11, C51, C53
- Replaced 1uF caps C15, C18, C19, C32, C41
- Replaced 10,000uF caps C20, C21
- Reseated IC U16 (I hesitate to replace the socket since de-soldering 24 pins simultanously is a pain)

This did not imporve the issue.

I connected a speaker to J6 Aux Out and the sound is distorted there as well. This means the problem is not in the power amp but further upstream.

Anoyone have any suggestions?

2 months later
#46 1 year ago

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?

#47 1 year ago
Quoted from arolden:

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?

Yes that sounds exactly like the same problem. No I didn’t resolve this. I would be very interested in hearing what you find out.

#48 1 year ago

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.

#49 1 year ago

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.

#50 1 year ago
Quoted from Robotworkshop:

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 have replaced the big caps. No ripple AC on the line. Did not fix the problem.

As arolden mentioned the distortion is only when a sound is playing. Between sounds their is no static.

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