HELP-Donkey Kong 3 - No audio

SCUBA King

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Donor 6 years: 2020-2025
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I have a very nice DK3 stack I would like to get finished up.

Both RP2A03 test good
Poking around the board with @philmurr audio probe I get different game sounds but nothing feeding the amp so out of the speaker I get zip.

I am using a jamma adapter with an amp built in. Yes that amp works.

I have tried finding schematics so I can track it further but the best version I can find is illegible.

Any help on where to poke if you know, or if there is a clean version of schematics, please send them over.

Am excited to button this one up. My one buddy is a huge fan and he's offered to play test it for me once the sounds work.

Thanks in advance.
 
Dang. Those schematics are hard to read. I'm not 100% sure. But here is my take on it. Starting from amp and heading backwards, it looks like the audio signal goes through R48, C20 and then pins 1 & 2 on the two RP2A03's.
Maybe start at the RP2A03's with the audio probe on those pins and see if you get audio. It might be that C20 has blown. But I don't think I've ever heard of one those going bad.


2025-04-16.jpg
 
Audio off both p1 and p2 of RP2A03 at 4M
Audio comes though both legs of c20 and can still be heard on resistor leg tied to c20. No audio on other side of r38.

R38 ohms out to exactly 100k in circuit. And 98k out of circuit

P1 nothing p2 static on RP2A03 at 5J
 
New LM3900 installed. Thx to @mhcapps at arcadechips.com, got majority of sounds back but constant static on the channel now also.

Will compare to mame to see what sounds may or may not be missing.


I know I round one when I pump the spray there is no sound effect which I think is incorrect.

Progress! More to report tomorrow.
 
I was gonna say, off the top of my head pin 5 on your LM3900 is probably dead! Yank it and put it in a Chip Tester Pro to confirm it fails all tests.

You beat me to it.
 
Removed RP2A03 at 5J. Static is gone. So problem has to be on that side now.

I played musical chairs with both, problem stays the same and CTpro tested both out of circuit to pass also so am ruling them out.
 
when you asked me I was going to say it's probably a bad op amp

I made you too good though, Scuba King
 
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