Neo geo weird sound distortions.

[Spunky_Bruiser]

So, I have a neo geo 4 slot board, I replaced the battery, it leaked, but I got to it in time before any real damage happened. I recapped all the capacitors and on start up the sounds seems normal. Metal slug intro seems normal (sound in game is all screwy 90% of the time) and Samurai Showdown starts in a distorted mess. I am sort of at a loss as to where to begin. I mean I would think the yamaha chip or in the audio section of the game board but outside of shotgun replacing all of those chips I figured i would ask here first and see if anyone ran into this sort of thing before. I have no idea if someone plugged this board in a jamma harness to test it and maybe blew out the amp chip or what that even sounds like.

Here is a video of what it sounds like. https://www.youtube.com/watch?v=F4ZHegl-DIc

 

[mecha]

sounds like amp to me.

 

[Spunky_Bruiser]

That would be the yamaha chip right? The big old one. Are they a standard chip or do they need to be programmed. I was looking at a few different places and some videos contradicted each other.

 

[mecha]

no the Yamaha chip is for FM generation, it's a synthesizer chip. the amplifier is always mounted to a heatsink. I'm not familiar with what the part number is for those, so you'll have to triangulate with me later on that.

when amplifiers fail they'll be garbly and distorted or will cut out completely when they get hot or overdriven (ie. volume too high) improper impedance speakers will stress them as well, majority were for 8 ohm speakers, if you're running 4 ohm speakers that'll burn it out.

 

[Spunky_Bruiser]

Well there are only 2 that have any sort of heat sink in the audio section ( really the only part I looked. Well, the good news is, I have a completely roached out one slot board I doubt I would have time to get around to so I should be able to salvage parts from that I hope.

 

[mecha]

or this is what replaces it:
https://www.twistywristarcade.com/sound-amplifiers/1121-ha13001.html

 

[Spunky_Bruiser]

I swapped out the sound amp and well, I have some results,... Overall, I think Metal slug sounds better in game play, I think a few less screechy areas but the distorted sound persisted in some areas. ... Samurai shodown,... well,... we have NO sound now. So, we have some results! yeah,... Makes me wonder about the yamaha sound chip. If I had a tool to check the dac chip pin 4 I would be on that.

Also in the neo geo sound test I was able to hear normal sound coming from the right, left and I believe center sounded normal as well.

 

[mecha]

it could be a bad op amp too.

 

[JohnnyArcade]

How does it sound in test mode? There you can separate left and right signals too (if that helps narrow down at all).

 

[Spunky_Bruiser]

Johnny both of them sounded good. Left sounded good, right sounded good. Center i believe sounded fine as well.

 

[LinguistiX]

When you say "sounds all screwy" do you mean like it's screechy? Or is it clearly defined sounds but played at the wrong time? Cuz if it's the latter it's like my problem where the Yamaha chip, once warmed up, would rapidly cycle thru every sound sample in the game currently playing. Nothing distorted, just all wrong. Yamaha chip cleared that right up!

 

[Spunky_Bruiser]

I will try the yamaha chip.. I need to take off the one from the parts board but doubt that will work with all the alkaline damage in that area but who knows. Will try that first if not order another one. Picked up a few of those sound amp chips as well just in case. It sounds like the video I posted. Not,.. right,.. yet left and right speaker in test seem to work fine with the tone. Metal slug sounded pretty normal, but as soon as samurai shodown starts you will hear what i am talking about. Screeching to a deafening madness,..

 

[mecha]

it's probably the cartridge or slot is dirty.

I've tried my usual eraser method on those years ago and wasn't very successful. I had to wash both the slot boards and all the cartridge boards in the sink with Simple Green in order to fix that.

there's probably nothing wrong with your sound section at all. often times if you wiggle the cartridges in the board you'll get a Z80 error (that's the sound CPU) or the sounds will just cut out entirely. and probably will distort and sound messed up.

 

[Spunky_Bruiser]

It was the yamaha 2610 ic chip. replaced that and sounds are working perfect. Now I have a second board that has weird sound ,.. Not just like that but who knows. I ended up with a surplus of 14 extra yamaha chips lol Might try and change it out for the heck of it.

 

[LinguistiX]

It was the yamaha 2610 ic chip. replaced that and sounds are working perfect. Now I have a second board that has weird sound ,.. Not just like that but who knows. I ended up with a surplus of 14 extra yamaha chips lol Might try and change it out for the heck of it.

Glad it worked! If you have a desoldering iron it's pretty easy to do. If you don't....heaven help you lol

 

[Spunky_Bruiser]

Neo geos r a mess to desolder. First cat kit I did on them I had an iron and a manual desolder pump. Longest kit I ever had to do. The trick now is use the desoldering gun on one side and heat up the other side with the iron. Makes it easier.

I think I am going to order another Yamaha chip size socket for the other 4 slot board and just unsolder the chip. I will check it in test mode first but from what I am reading it might be another yamaha chip problem. Hopefully I will have 2 working 4 slot boards,..

 

[mecha]

that's the desoldering technique bestowed upon me by channelmaniac. many Japanese boards of the era were multi layer like these, meaning the +5 and ground traces are sandwiched in the middle of the board. by virtue of the area in which those span, it's very difficult to clear the holes out using conventional methods.

the 2 temperature setting of my Hakko FR300 years ago when I was capping Neo Geo boards was intended for multi layer, and was utterly worthless.

I only suggest doing the double iron method if your tools are grounded like mine. years ago I touched my shack iron and shack bulb together and would wind up killing one or the other. I'm fortunately well beyond those tinkertoys now... but what a time it was. I had some pretty impressive kills back in the day when you consider how utterly trash those were to use.