Not really, I just did a re-cap, (de-cap/clean pads/re-cap) and swapped out the sound chip.
Acutely I didn't even wash it… maybe you should give it a good wash?
From my experience, the sound came from the Headphone jack just fine.
But no sound from the internal speaker,
and SCSI wasn't responding,
Floppy drive was not responding.
I have a hunch you could plug in some speakers.
Slap a Nubus scsi card in there
and a Nubus Video card,
It should be good to go.
Or just do what you have been doing, look for a replacement q840av mobo.