Nam MVS cart with sound issues

[-D-]

So I've got an MVS Nam and it has some sound issues. It seems to be mostly the sound effects that are affected, it sounds really crackly and overwhelms the music and pretty much ruins the audio throughout the game.

Though when I go into the UniBios jukebox it seems there's maybe 3 music tracks that are crackly as well, but most of the music tracks play normally in there.

Outside of the audio, the game plays normally though. I inspected the PCBs and everything looks perfect, no solder points look disconnected, all traces to the contacts look good, contacts are clean and look good.

Any ideas? I don't really have any experience with fixing this sort of thing.
Thanks.

 

[mjs256]

The nice thing about Nam 1975 is that it is an old board that uses standard ICs which are easy to obtain. For this reason they are also easy to diagnose. You either have a bad 74LS IC (most likely), a bad V-ROM (semi-likely), or a bad M-ROM (very unlikely). The best way to determine which is the culprit is a logic probe. I have some experience fixing these, but I am really busy so it might take a long time for me to get to it.

 

[Lemony Vengeance]

Xian Xi May be able to help you. Send him a PM and I'm sure he'd be willing to fix this

 

[ne7]

before you do any poking about clear your battery ram (via unibios test mode) or just boot the board with all dips flipped to on as this will do the same thing once the test is done \o_ had both nam + burning fight exhibit the same probs before and just clearing battery ram fixed it

 

[-D-]

Thanks for that tip ne7, good to know for the future; though it didn't fix the problem.

 

[ne7]

ah damn, best of luck with it \o_

 

[Xian Xi]

Just an update, he sent me the cart and it turned out to be a bad LS174 that was connected to V22 and V23.

 

[Lemony Vengeance]

Just an update, he sent me the cart and it turned out to be a bad LS174 that was connected to V22 and V23.

Told you he could fix it. Now if memory serves me correctly, this is the 2nd copy of this game you own, right? wanna hook a local up? :P