NeoGeo (MVS-4F) Issue with Sound

toloqi

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Ok, I have had this MVS-4F for a while and I am working on fixing this audio issue I have. So far here are the traits and what I have done to try and fix it.

Problems:
- On start up and sometimes during play it will make an escalating clicking noise very loudly. The volume of the speakers doesn't matter, even completely silent it makes this noise.
- If I disconnect the speakers completely I do not get the noise at all
- Using the headphone jacks from the front and hooking up speakers it sounds great with no issues.

What I have done:

- Installed an audio cap kit (courtesy of arcadecomponents.com.. woo plug!)
- Tried another board to verify it isn't crazy wiring or speakers (it isn't)

The cap kit did change things as the sound now is a bit more crisp as well as the clicking sound now at the tail end makes kind of a dying gerbil noise. Or the sound one makes when he realizes all of the oreos are in fact gone. Oorororoorooo..pss..

While playing a game it seems like it only causes it to make this annoying noise when a loud sound is played through the speakers. I will try to get an audio clip at some point so you can hear it, but I just want it gone. The work around works, but overall the speakers sound so much nicer :) I want the board to work well.

TIA everyone :)
 
Probably a bad amplifier chip if the audio via headphones is good, and you have replaced the caps in the amp section. Check that there are none missing, or any other damage in the area, then replace the amplifier chip.
 
Thanks for the plug :D

Before you replace the amp chip there are 2 big poly/mylar caps in the audio output section - after the amp but before the 470uf caps you replaced as part of the kit.

Desolder those 2 caps and see if the noise goes away. If it does then it's a problem with the amplifier oscillating. I've run into that 3 or 4 times before. Pulling those caps makes it go away.
 
well, looking around the 470uF caps I found the two big poly/mylar caps and desoldered them, being careful to leave legs to reinstall if needed.

The sound is gone! :D And the audio is extremely crisp now.

One question though, what are the ramifications of leaving those two caps off? Surely they didn't just throw "extras" on the board. This is just a home use system so mainly it will be on for a few games. Maybe 2-4 hours maximum at a time.

Also, is this a common issue? You seemed to hit the nail on the head quite quickly :)

(by the way, if you need a picture of an MVS-4F board for your pdf let me know and I will try to take some nice pictures of mine and send them your way. I can even put the mylar caps back in the picture for you :D)
 
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I do need a pic of that board and would appreciate it!

I ran into that noise before and pulled my hair out like crazy. When it oscillates like that it can pull enough current on the 12v lines at higher volumes to cause the 5v to dip and the board to reset! It took me a couple of hours to track it down and I've only ever seen it on the 4F.

Removing those caps cause no ill effects that I've seen/heard of. The folks I fixed that issue for are still running theirs. :D

RJ
 
Will take a picture of the board next time I pull it out, but now I have a new problem :)

My power supply is a brand new power supply and seems to have no trouble powering my other board or this board before pulling those mylar caps.

After pulling the mylar caps the clicking is completely gone. However, now I have your typical "needs an audio cap kit" audio problems.

After playing it for a bit (10-15 minutes) I noticed that the foreground audio (voices, sound fx) are all fine, loud, crisp, but the background music goes in and out.

It doesn't do it all the time, but a definite fluctuation where you can't hear it at all to normal volume. It does it quite rapidly. I may see about getting new mylars and seeing if that will fix it, or does this sound more like audio amp issues?

The only caps I didn't replace were the two 470uF for the power (looking at the Jamma pinout to find the power).
 
Never seen that one before... It all comes through the DAC chip so you should lose all of it or none of it. Sounds like either the YM2610 or you have an issue with corrupt Backup RAM.
 
In the intermin, put the mylars back in, it will prove if it is a new fault, or related to their absence.
 
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