Nintendo Vs Red Tent PCB Audio: I only get sound on side B of the cabinet

davesies

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Hey everyone, new forum member here. I am very new to the arcade cabinet ownership journey, I recently acquired my first arcade cabinet, a red tent, and I excitedly picked up a few boards from someone else here on the forums. I'm having an issue with one of the boards though which seems quite odd. I get no audio on side A of my cabinet. I'm quite certain the issue must be with the PCB, as I have a Tennis PCB and a SMB1/Gradius board and both get sound on both sides with no issues.

I've looked up the pinout diagram for the connectors and carefully cleaned the X/20 pins with a pencil eraser and 99% isopropyl alcohol in case it was just a bad connection, but no luck still. Visually inspecting the board, I can see a couple suspicious traces on the backside that look like they've potentially been damaged, but I'm not sure really what I'm looking at in terms of the circuitry of a Vs board. The strange thing is that literally everything else works fine about the board as far as I can tell, the game plays fine and I get sound from the B side of the cabinet.

Does anyone here have any suggestions or experience debugging this kind of issue? In case it's important, the game installed on the board is Balloon Fight, though it seems to be a romhack/reproduction since the PPU type is 0001, as opposed to the 0003 PPU which seems to be what the original game used. I doubt that's relevant, but I figured I would add that info just in case.

Thanks in advance for any help!

Edit: PS sorry for the pictures being kinda low quality, the forum kept complaining that they were too big, but I worry maybe it will be harder to identify the problem at this level of quality.
 

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I didn't read everything but both monitors have separate amplifiers. Also I've heard ppus can cause sound isues
 
Interesting about the PPU. I'm fairly sure it's not a monitor amp issue because as I said, I get sound on both sides from other PCBs. One thing I do intend to try at some point when I have time is to actually remove everything and plug it into another board that is known to work so that I can see what happens there and maybe confirm it's a PCB issue.
 
Thanks for the suggestions! Since both of those chips are quite cheap I decided to just order them and see what happens, will report back if that fixes my issue.
 
Thanks for the suggestions! Since both of those chips are quite cheap I decided to just order them and see what happens, will report back if that fixes my issue.
Out of curiosity, I am not exactly an expert when it comes to following circuit boards, though I have some comfortability with soldering as I've done RGB mods for all my Nintendo consoles, but could someone help me to identify which of the two LM3900 and LM324 in the photo are the ones that are associated with side A of the cabinet?
 
Go to 6:55 in this video. It tells you everything. Awesome series.

Not sure if they are a member here.

Oh wow amazing resource, thanks for sharing! Will report back once I get a chance to swap these chips out if this fixes my audio issue.
 
Update on this: I now believe the issue is that I had a bad CPU. I realized this when I ran into another audio issue that was even more bizarre. After leaving my cabinet on for a few hours, I realized the pitch of audio on my side B would get lower and lower with time. I figured this likely was a CPU issue and I replaced the CPU with my Balloon Fight side A CPU. Then when I booted up the other game I was testing, I got no sound at all.

I guess the APU must give out occasionally on these old CPU chips. Thankfully it's still not too difficult to find replacements for these.
 
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