Battle Garegga sound issue

[safetyboy]

My Garegga PCB loses sound of vocals and bombs and the likes but retains the music and bullet sounds, I've reflowed all the sound section and it still happens, Could the yamaha YM2151 have gone faulty, Its strange that the music still plays. Or would the OKI chip be at fault, I got this reply off the seller.

"I am very sorry for this situation....
possible reason is Amplifier or OKI6295... or another ICs..
but background music works... so amp is not bad
I think maybe OKI6295..it does sound effect.. it's connection is not good etc..
but I cannot understand.. why boss stage....

Could you adjust +5 volt higher? for example 5.2volt 5.3volt etc..
of course.. adjustment +5 volt need delicate careful dangerous process.. at POWER OFF..

and at working condition.. jamma connecter and pcb need a firm foundation.. for avoid shaking"


Also what does RV1 adjust in the sound section?

[system11]

RV1 is the volume control..

Reflowing things randomly isn't going to help here - the most likely problem is indeed the OKI chip, you need to check all the leg joins are good on that first. Take a very small craft knife or similar, and go around that chip GENTLY trying to move the legs sideways. If you find one that moves, you need to reflow that leg.

Any further diagnosis you'll need logic probes and oscilloscopes for.

[safetyboy]

I went through it in work under the scope, the chip has been replaced before, so I reflowed all the legs. (I work with hearing aids by the way so I am used to working with surface mount bits.) All looks good on the board, but I can play for an hour and its all grand or I can play for 5 minutes then the SFX goes. strange. I've tried in 2 cabs now and both the same. Its a Korean PCB with Zakk roms, can the Z80 effect the sound as I have about 50 here at the moment?

[system11]

Have you tried putting a slight amount of flex on the board while it's working?

If the time to fail is random then it could be a trace fault. Another possibility is your +5 - have you checked it? It won't be the Z80 because if that stalled the music would die too. Have you checked the OKI output with a scope to check that it's not something in the op-amp section? If the OKI is stalling but the rest of the sound continues, it could potentially be problems communicating with the sample ROM.

I'd also try dropping normal Korean ROMs onto it, just to rule that out.

[safetyboy]

It came with the Korean roms so got some Zakks off AO, I can replace the OKI no problem if I can find one I might recap the sound section first. Just seems weird that it happens randomly. It really takes away from the game when the SFX go. I'll keep note of all changes I do anyway for future reference.

The Jamma Connector has been filed down too, doubt that has much to do with it. Who doesn't love the Boomba FX?

So does the OKI chip hold all the vocal samples? They must be stored in an Eprom?

swapped my Oscilloscope for a juno 60 a while back, whoops!

[trap15]

The samples are on a mask ROM, the OKI is the sound chip that plays them.

[safetyboy]

So you reckon the OKI is at fault? board looks clean under the microscope, are the PCB more than double layered? I wouldn't think so in 1996?

[trap15]

It's double-layered. My guess would be the OKI, personally.

[safetyboy]

Any links to a new OKI, tried ebay, nowt coming up from Ireland.

When I get to work on Monday I will remove the OKI and clean up the traces and resolder it back, might be a short underneath as its been replaced before.

[system11]

AD65 and U6295 are Korean and Chinese clones, you might find those.

[safetyboy]

A chap on AO reckons it could be MSM6295 voice synthesis IC, cant see any on ebay.

[system11]

All the same thing... that smt chip, see my last reply for equivalents.

[safetyboy]

cheers for the help

[safetyboy]

Ordered a clone from China, I'll let you know how it goes.

[safetyboy]

Its alive, cheers for the help.



OLD



Gone





New chip works

[system11]

Edit: removed chip removal tip, have since discovered it is not safe and can lead to damage.

You want to buy some chipquik to remove these if you don't have a proper removal station.

[safetyboy]

Looks like this has died again, I think it could blow by voltage as I tried it in my NNC after a month of not in use, looks like I gotta grab another chip, I'll leave it in the egret from now on.