The DSP on the board is responsible for volume. The MPU will command a volume setting to the DSP. I’d be surprised if there wasn’t a feedback message to the MPU; a closed loop control system.

The DSP does all of the “digital” work on the board as DumbAss was saying above.

The DSP accepts sound commands from the MPU. It then pulls the sound data from the ROMs and pipes it through the digital to analog pipeline.

Sound ROMs are checksumed by the DSP.

But S2 can be the wrong S2 and the DSP would never know.

I’d verify S2 as the next step.
—
Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

Your soundboard is like every other DCS soundboard. There was no variation in that board over the run of DCS games.

There are two ceramic capacitors adjacent to the heat sinks, which are sometimes removed. Yours have already been cut and are out of circuit.

Is the volume excessively loud when you set it below eight?
—
Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
Thank you for checking out the PinWiki - http://www.PinWiki.com/

PBlank
With some sounding board and additional information help from @dumbass, this board is now working 100%.

Short Story...
As is becoming quite typical, the 100uf/25V power input filter cap had leaked it's caustic contents onto the board.
The "acid-like" goo severed a trace that connected the 74HCT374 input buffer to the ADSP-2105.

This had two ramifications and one puzzlement:
1. Even though the MPU comms with the sound board were less than 100%, no "sound board interface error" was indicated.
2. Although volume control from the MPU was commanded, and the DMD volume indicator "thermometer" was behaving normally, setting the volume to anything between min and max had no impact at all on actual audio volume. Volume remained at what I'd estimate as a normal "12".
3. During sound test, at least some of the commanded sounds were replaced by other sounds.

Video later.
Thanks again DumbAss for the nudges.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Video showing damage, repair, and test...

--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info