...and, the PinSound board has (or had) an incompatibility with RottenDog MPU boards in WH2O. It would only work with an original WPC MPU. I don't know if this problem has been fixed.

I'd start with the easy stuff....ribbon cables. Reseat the ribbon to the sound board at all 4 points where it connects to the MPU, FlipTronics, Sound, and Dot controller boards.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

OK...You probably have another pre-DCS game.
There are several socketed ICs on that board.
You can swap them, one at a time to see if that fixes anything.
The YM2151 and the 3012 work in conjunction.

The X9C503 digital POT on the board fails fairly often, but usually the failure manifests in a full blast volume jump.
After swapping chips, if that doesn't yield results, you can "listen" to the analog signal at various points with a logic probe. I put quite a bit of info in the PinWiki about this board.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Start by placing your WH2O ROMs in the spare board.
Test.
Next swap the 68B09EP from a known good board to the suspect board.
Test.
Next swap the YM2151 from a known good board to the suspect board.
Test.
Then the YM3012....
That will have exhausted all of the "easy" things to do.

After that, if it's still failing, wait for the failure then put the meat of your index finger on the RAM chip (it has the serial number sticker on it in the picture). Determine if it feels abnormally hot. If it has a sticker, is the sticker burned?

Carry on soldier.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Yep. The replacement from Marco will work fine.
Tantalum caps are polarized. Note positive and negative when installing the new cap or you'll get a quite spectacular explosion.

Those tantalum caps give up the ghost once in a while on the pre-DCS sound board. It's not very unusual. Simply replacing the cap should get you back in business.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Zara to the rescue again!
For future reference, we also have board pics in the PinWiki that can help with part locations and identification.
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Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

Those are electrolytic caps. They are necessarily larger than tantalum caps. They will work. Take note of polarity.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

BigFoot mad....!
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info