Donkey Kong 3 no sound. Board issue.

rabid bear

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Have a Donkey Kong 3 that has no sound. I have tested the board set in another Nintendo cab and the issue carries over, so it isn't the usual monitor sound board culprit. Issue is on the board itself. Boards are currently in the cage but will be removing them so as to connect directly instead of to the filter PCB. The schemes posted online are a bit difficult for me to read and to be frank having difficulties sorting out the sound circuit in them.
Thoughts? Suggestions as I pull the boards out of their cage?
 
Got this fixed tonight after a false start last night.
Pulled boards out of their cage and after separating found a lifted burnt trace right away. After much squinting at the on line schemes determined trace was going into the LM3900 quad op amp. It looked a bit toasty so decided to replace as well as jumping trace. Got old chip off, new one on, and trace jumpered nicely. Plug in board set and fire up to be met by smoke and burning electric smell from board set. After cursing myself look at the monitor and discover what had caused the sound to go out in the first place. JC and JB backwards on amp card.
Pull board set , another burnt trace on that circuit and LM3900 looking crispy again. Jump trace, another LM3900 and get the distinctive Nintendo hum but board isn't booting. Replace Z80 and everything boots and I now have sound as well.
 
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it sounds like JB and JC are reversed on your audio amp
 
There is a wire running from your audio adjustment pot with a grey shielding on it. is it running over to JC on your audio amplifier at the chassis because if so you repaired your board and then blew it up again.

They can easily be mistakenly swapped and they are keyed the same. I've seen this a bunch and have even done this myself by accident
 
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