[Solved] Super Punch-Out: missing music channel audio

MaximRecoil

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[Solved] Super Punch-Out: missing music channel audio

This is TapperAdict's boardset. He sent it to me to check which ROM set version he has (it is the standard version), and while I have it, I'd like to get the audio working. Here is his explanation of what happened to it:

Yeah, So what happened was I took the bottom monitor in for a cap kit and a rejuvenate. That monitor has an audio board inside the chassis. There are two gray cords that actually have the same connector type. Those got switched at the monitor level. So the power went through the Audio board in the monitor (instead of powering the monitor) and then out through the audio cord and fried the audio section of the board.

The video and the speech channel audio are fine, but there's nothing but dead silence on the music channel (left speaker). Here's a picture of where all the visible damage happened:

jj6g52U.jpg


The green wire is to replace a trace that was completely burned through. I also replaced those two C1815 transistors (Q1 and Q2) with new ones. The R69 1 Kohm resistor and the R68 180 ohm resistor were burned and replaced as well. I can't see any other traces that are bad. The rest of them visibly look good and I've checked continuity on the ones that seem relevant, back to the card edge pins.

Also, I've tested both the 2A03 CPU and the EPROM at 4K and they are both fine. I don't understand electronics circuitry in-depth like some of you guys do, so I'm out of ideas. For reference, here are the schematics for the CPU board:

https://i.imgur.com/Ku9z3BH.png
 
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Based on the schematics, it looks like the next major thing up the line from those two transistors that I replaced, is an LM324 at location 2N, which is a quad op-amp. The part actually installed in the board is an LA6324, which Google tells me is the same thing as an LM324. LM324s are still available to buy new from Digi-Key or Mouser for ~50 cents.

Does the LM324 seem like a likely suspect?
 
Could be but I would check all other components in that final amp stage as well: R66, R67 and C37. If all those check out then yep, I would go for replacing the LM324. We know at least 2 of the 4 internal amps are working since they're used to amplify the speech as well but who knows... maybe the other 2 got knocked out.
 
Could be but I would check all other components in that final amp stage as well: R66, R67 and C37. If all those check out then yep, I would go for replacing the LM324. We know at least 2 of the 4 internal amps are working since they're used to amplify the speech as well but who knows... maybe the other 2 got knocked out.

Thanks for the reply. I just pulled the LM324 from one of my spare Punch-Out boardsets, installed it (along with a socket) into TapperAdict's boardset, and that fixed it.

I'm pretty sure that at least one of those C1815 transistors I replaced earlier was bad too, because I couldn't get any readings when testing resistance between the base and emitter or between the base and collector. I got readings when doing the same thing with the identical transistor right beside it, but I replaced that one too for good measure.
 
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