I am having an issue where all my sounds and speech are working but the volume is too low. Here is what I have done so far:
Recapped the ps and sound board.
New headers all around.
I eliminated the main pot as the source.
I eliminated the speaker as the issue.
I replaced the transistor that drives the dac

I am not sure what to test next honestly. I did check 2 pins on the dac per an old thread, but that didn't show an issue. Hoping someone can help.

I am thinking it may be a sound ampliphier, but I do not know how to test one.

Touch with my finger? Thanks

Ok, so I get nothing when I do that. I think I see the input pin on the schematics, but how much voltage should I see there? Also, does it always how power or just in gameplay? Thanks for your help!!!

Thank you! Yes, that looks like the same schematic. I will double check though.

Ok, so at pin 5 I am getting 10.75v is this close enough?

I know the caps are correct value and polarity, but there was one listed as "low leaking". I put a ceramic cap in this spot after trying an electrolytic first. It was originally an electrolytic. I ordered a tda2002 and figured I would swap it out and see.
I also tried a second speaker to test that.

Well, I swapped out the tda2002 and still the same issue. I notice that I am not getting much wattage at all if I read the volts at the speaker. I did check all the resistors around that amp and they read good. I am kinda stumped again.
I know the data signal is good since I get all the sounds. I still get no loud hum if I touch the legs of the amp. All test points show proper voltage.

Ok, so by swapping out my sound board from BK, I have full sound and speech. Now I know the issue is on the sound board itself. I am digging through the schematics to the best of my ability, but nothing pops out at me.

I did put the gorgar rom in it. The only other thing I could swap is the 6808. I will do that next and at least eliminate that. I don't think a pia would do that though, would it?

I swapped that out with no change so the pia is good.

I guess I can compare votages at certain components between the 2 boards and see if that shows anything.

Can anyone tell me what this circle is?

20210508_124049 (resized).jpg

Screenshot_20210508-124002_Drive (resized).jpg

Problem is I already replaced the caps and the amp. All those resistors read in spec. Not sure what else to replace.

I am gonna swap out the ceramic caps next but for the 100v ceramic, I only have a film capacitor in that voltage. Hoping that is OK.

Still the same issue. I notice that c12 and c14 have more voltage on the broken board. 1 4v compared to .69v. Not sure what to do next honestly.

Replacing everything on the output, even the resistors that read fine. If I have input voltage and a clean output line, I should at least get a loud hum when touching legs, right?

20210509_162407 (resized).jpg

Yes! It is working now! I did test each resistor, but they are labeled on the paper. Not sure if it was a resistor or one of the new caps were bad, but I replaced them as well.

Thanks for your help, everyone!

16206075623982854360556430652011 (resized).jpg