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16B - line level audio noise

plasticfactory

plasticfactory

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I'm having an issue with a lot of line level audio noise from my 16B. The setup:

System 16B (Aurail) > 16B to JAMMA adapter > JNX MVS adapter > Neo 25 cabinet

I have already fully recapped the board, but the issue persists.

Where should I look next?
 
By ‘line level’ do you mean it’s been converted from amplified audio to line level audio by the MVS adapter? Do you have any issues with any other boards through this adapter?
 
I'm probably using the wrong term. I just mean when no audio is played through the board, there is a lot of noise. Happens regardless of cab/adapter.
 
Ok. So a recap hasn’t improved the output? Have you replaced the film capacitors or just the electrolytics?

Do you have access to a scope? It might be worth looking at the op amps (LM324, TL084) and audio amp IC (MB3733). A scope would make it easier to check which is at fault though I would check/ replace the film caps first.
 
Correct, no improvement from recapping. I did not replace the film capacitors or the super cap (the one in the kit didn't fit and I haven't ordered a new one yet). Functionally, what are the film caps doing on the board?

I'm assuming because everything is working, I need a scope over a logic probe?
 
Don’t worry about the super cap. If your system is mostly working then it’s not a problem for now.

The film caps are used for signal smoothing and setting the bias on the op amps. I can’t say why the designers specifically used film caps on the Sega System 16 but they are used for almost all caps under 1uF on the board and traditionally accepted to be better for audio, non-polarised and self healing so that may have been a factor.

It’s not essential to have a scope but would make it easier to decide what to replace next. Without a scope, I would look at replacing the film caps and op amps first.
 
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