Donpachi PCB sound issue

[jepjepjep]

What chip is used for the sound effects on Donpachi? I get occasional static pops during the sound effects and every once in a while the sound will cut out completely during the middle of a game. The music will continue to play but the bullet sounds, announcer, and explosions will be gone. If I power down the board, the sounds will come back but with the occasional static pop.

Could it be a bad capacitor or bad amp?

[trap15]

The sound chip used for both the music and the sound effects is none other than the OKI MSM6295. There are two of these, one for music, and one for sound effects. It's entirely possible that the chip itself is failing, but it could also be that a capacitor or amp before the two chips are mixed is failing. Someone else here probably knows better than myself about fixing this problem though.

[jepjepjep]

Are the two sound chips the surface mount ones at U22 and U24? My board is the international version and those chips just have AD-65 silkscreened on them. I wonder if they're a cheaper brand chip. This pic is from the world-of-arcades site. I can barely make out the silkscreen but it looks to me like it says OKI M6296.

[trap15]

Yup, those ones. That theory about the AD-64 is probably correct, but I couldn't say for sure.

[jepjepjep]

Oops, I meant to say AD-65.

[jepjepjep]

I have a couple of OKI M6295 chips from dead CPS1 A-boards. Is there any danger in putting on the 6295 instead of the 6296? Also, any idea which of the two chips does the sound effects and which one does the music?

[trap15]

I said 6295, so that should be fine. Not sure which is which, however.

[jepjepjep]

Thanks for the help trap15.

[robivy64]

Don't replace those chips blindly without checking with an audio scope or o-scope first. You may be wasting your time otherwise.

Before replacing chips, start with the easiest troubleshooting step: clean the volume pot.

[system11]

He says the music keeps playing - therefore we know it can't be the volume control. It could be a cracked solder join though near one of the op-amps, and it could easily be an op-amp failing as it gets warmer. Really needs someone with an oscilloscope to check it out - very easy to just scope the OKI chip output then while the effects have cut out to see if that's still making them. That key question tells you which direction to go next.