I've got a Fish Tales with the standard WPC Audio Board (A-12738) that have worked fine until a few days ago when the sound (both music and callouts) have started to behave strangely while playing. The issue is that the sound comes and goes randomly; sometimes it slowly fades out (over a few seconds of time) and I can only hear the sound faintly and then it will fade back in again later. Other times it just vanishes completely and a random time later comes back again with normal volume. Loosing a ball and progressing to the next one doesn't remedy the problem if the sound is weird at that moment.

The problem can appear within a few seconds after turning on the pinball machine (not played at all for a whole day) and then starting a one player session, so probably not directly heat related.

I don't have an instrument to measure the temperature of the large heatsink but holding a finger on it is no problem; the heatsink is warm but won't get hot.

When I put the game in test mode for sound and kept it playing it worked flawlessly for several minutes without any issues. I then let the sound test continue playing while wiggling/pressing on all PCB connectors on the sound card that have cables connected and sound works just fine without any problems.

As a side note, the original CPU card had a problem after leaking batteries when I bought it about a year ago so I replaced it with a brand new card, so my current issues shouldn't be related to the CPU card at all.

I have not replaced the ribbon cable going to the audio card but wiggling it around in music test mode doesn't introduce any audio problem, coupled with the fact that the DMD behaves 100% all the time and is located on the same cable make me think it's ok.

The issue seem to be present only when playing (so far at least), could that indicate it's a problem with failing voltage input to the card when other things are in play like coils, flashers and other PCBs drawing power?

I've never had sound problems on any of my games before so consider me a newbie on this front. I can't find any dedicated test points on the card (like on the power driver board) so I guess I have to measure directly at the incoming connectors. Should I measure for 18 V AC between J501-1 and J501-4/6 and for 5 V DC on J502-1 to any ground?

I'm aware that many replace the old capacitors on this card. My understanding is that is done when sound gets distorted/sound bad but is not related to "volume" problems similar as mine, or am I wrong? Should I just shotgun it and replace all the normally recommended capacitors and see if it helps? Visually all components on the card looks good, nothing burned, no leaking or bulging capacitors.

Any help appreciated.

Thanks for the suggestions, I will check the speaker cables/connectors more thoroughly.

Removed the audio board and checked all connectors soldering with a magnifying glass, no problems there.

Also removed both speaker cables from J505 and J504, cut the ends and pressed them back in.

Inspected the speaker cabling to both speakers in the backbox (not the cabinet one) and all cables are fastened firmly with good solder.

Playtested and within 1 minute the sound faded out and in again. Sigh...

Maybe I need to change that x volume potentiometer chip mentioned in the thread above.

Sorry for being silent here. This issue got interrupted by a complete TOTAN teardown/rebuild which were finished today, so now I will get back to this sound problem again.

I did receive the two recommended ICs to change a while ago, just not sure which one to replace first, any suggestions?
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Short update.

Before I changed the ICs I wanted to verify that the problem were still there, just to see the difference before/after soldering.

I played for about 45 minutes yesterday and to my surprise the sound worked perfectly. Tried to provoke the issue by nudging, banging on the backbox and so on but sound were ok.

Played again today about 30 minutes and still no sound issues?!

If I change the ICs now when everything works then I won't really know if that changed anything or not, so I will wait with the soldering until/if the problem reappears.

If it does I will start with replacing 9503 as suggested and report back here. Until then I will consider this issue temporarily fixed.

It's the original soundboard as far as I know yes.

I haven't removed the board ever. The only things I've done on it is checking the fuses and removing both small speaker connectors (J505, 506?) once but I still had the sound problem after that.

I haven't touched the board since the sound problems about a month ago until now (because of the totan restoration) when it just works again. I have no explanation as to why it changed behavior.

You are correct, I did totally forgot I had done that earlier, sorry.

Anyway, the sound was still problematic after I had inspected the card and put it back into the game and I haven't touched the pin since then because of another game restoration (and waiting for replacement IC parts, that takes a while to get to Sweden) and now I can't seem to reproduce the issue.

Short status update. Have been playing the game quite a lot since last posting here and sound still works fine, no idea how it "fixed itself" but I'm happy as long as it works.

Maybe I've jinxed it now, we'll see

The game just recently began having the same sound volume problems again.

I've just replaced the X9503P IC and hopefully it's fixed now, will have to play the game a lot and listen. Running sound test for about 5 min straight sounded ok anyway but not a realistic test without vibrations and heat from playing. Time will tell.

Edit: sound still change volume while playing so I also swapped the MC3340P IC and played just a minute or two before the sound acted up again. Clearly my problem is something else on the soundcard

I took a magnifying glass and tried to look over the complete backside of the pcb for cold solders or similar but couldn't find any. Checked the used connector header pins especially but all looked fine to me. Resoldered the five legs on the transistor mounted to the large heatink just in case but still sound problems.

All music and callouts sound fine while running through the sound test mode so I doubt it's a sound ROM issue.

After playing a while the heatsink gets rather hot. I can hold a finger against it about 7-8 seconds then it hurts a lot. Normal behavior?

Soundcard looks to be in good overall condition to me, no old fixes that I can see.

What to do next, any suggestions?
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Was googling and found this snippet of info(from Clay's repair guide?):
"...
Main amplifier is bad: On pre WPC-DCS games, the sound board uses a LM1875 as the main amplifier. This device has a large heat sink attached to it. Often, this component has heat failure. The sound works fine until the game warms up for five minutes or so. Then the sound starts cutting in and out. You can use a logic probe on the leads of the LM1875. If the probe's beeps correspond to the cut in sound on one of the leads, the LM1875 is probably bad. The LM1875 is at U1 on the WPC audio board (not used on WPC-DCS or WPC-95).
..."

My heatsink that U1 is fastened to gets really hot after a short while. I currently don't own a logic probe so can't test it as described above. Should I order and replace the LM1875 or any better suggestions?

Also found this @ pinwiki:

"6.31.5.6 Popping, Scratchy Sound, Very Hot LM1875 Heat Sink, or Shorted Speakers
...
Normally, the positive side of the tantalum cap at C26 will measure about 50mv of AC referenced to game ground. Anything more indicates a problem with these tantalum caps. You will also be able to measure DC voltage across the speaker outputs. There should normally be no DC voltage across the speaker outputs.

The LM1875 may also run very hot. Normally, you can grasp the heat sink without burning your hand. It will be hot, but not so hot that you can not squeeze it or grasp it very long. Note: this assumes that the volume is set to about 8. Setting the volume to 18 will require the heat sink to dissipate more heat. The heat sink will be too hot to grasp (for very long). If at "normal" volume levels and the heat sink is so hot that you can not grip it, failing tantalum caps should be suspected. If after replacing the tantalum caps the popping and scratchiness persist, the LM1875 amp may have been damaged. "

So I started continuous sound test and let it run for a couple of minutes (at sound lvl 7), then measured AC between C26+side to ground and "only" got 0.10V, so far from being above the 50mv in the pinwiki test. Did a visual inspection of the tantalum caps and they looks ok, nothing burned or discolored.

Also did measure DC voltage between the two speaker lugs on the left small speaker and reading were 0V so seems ok.

Then I realized that when the sound volume changed to lower/silent I could then bang on the cabinet and the volume got back to normal again. Tried it several times and worked the first hit almost every time. Tried hitting both the cabinet and the backbox but couldn't really see any difference in behavior, guess the vibrations always goes through the whole machine. Also tried "wiggling" the big heatsink by hand when sound were gone but that did not bring the volume back up.

Lastly I checked the large speaker in the cabinet bottom and verified the lugs were seated properly, no visible cracks in the solder. Removed one speaker spade connector on the large speaker and measured it to 3.5 Ohm (marked to 4) so about normal resistance and no short there.

If feels like I'm just shotgunning all over the place and don't have a proper plan troubleshooting this.

Problem is probably fixed, time will tell.

After more googling I found info about a HS2 with distorted sound. Owner replaced the usual capacitors and the amplifier on the large heatsink but problem were still there. His heatsink got very hot after a few minutes and my game had that behavior too. He fixed his problem by resoldering all soundcard connector pins.

I had already looked at my solder points using a magnifying glass earlier and couldn't see any cracks or similar but decided to just reflow them all (J501-502, J504-506) just in case. After doing that the sound problem seem to have vanished. I played more than 40 minutes consecutively (while occasionally also banging hard on the cabinet to induce vibrations) without any sound error. The heatsink that I could barely touch more than 6-7 seconds is now considerably cooler and there is no problem touching it for 20+ seconds. This makes me believe it's actually fixed now.

Don't have equipment to measure temperature but it's noticable cooler so reflowing did help somehow. My guess is the amplifier worked with wrong voltage or bad grounding due to some crappy solder connection and got too hot.