sega megadrive model 1 sound problems

i accuired a sega model 1 today in the mail it's been region modded however the sound goes messed up as long as i havent thrown a punch in streets of rage 2

i thinks its the sfx it goes boom bang messed when i start attacking ppl i uploaded a video on youtube

http://www.youtube.com/watch?v=bBe5PURWCeM
Any ideas?

 

If someone has any ideas it would be really helpful. I supplied the Megadrive and I'm the one who modified it, it was absolutely perfect before I sent it. I really want to help masterturk sort this out, so even if it comes back to me I need to know how to repair it.

Thanks.

 

Sounds like some crossed wires or a solder bridge. Seems similar to a circuit bent MD.

 

The PSG handles sound effects, find that on the PCB and check for solder/swarf.

 

i have checked the insides and have found no excess solder. After a while of playing the game also just hangs and i have to reset...

 

Bad cart? Does it happen with the SFX in other games?

 

I doubt its a bad cart i tried it with moonwalker and there is no sfx just annoying noises instead, when im playing the game the megadrive lags and sometimes just freezes and i have to reset...

 

Did Twimfy overclock it by any chance? Certain clock speeds can cause the 68000 to be erratic.

 

No I didn't.

Just region and Hz rating. Masterturk is using the system via RF not RGB or S-video but he's reporting this sound through the headphone socket too so I doubt that has anything to do with it.

My personal MD1 is the same model as this one (a VA4 motherboard) I did the mods on these within a day of each other and the one that Masterturk has was my play system while I was waiting on parts to finish the one I use now. So I know it worked fine, I really cannot think what has gone wrong.

My only guess is that a solder point has broken or has a bad connection where I modified it and this has been exacerbated by the postman.

 

I agree with Twimfy. A loose connection or snapped wire is most likely. Twimfy, was there anything protoboarded in there? Stress on some of the joints could do it. High-res pics of the board would be nice.

 

If you want to check if it's the PSG or FM Synth chips (I personally think it's unlikely that it has problems with the PSG as it's part of the video chip) use Sonic The Hedgehog as the jump noise is played by the PSG. :thumbsup:

 

Are those colors normal on your TV? And is it rolling or is the camera having bad luck?

Since you say the system is slow I think possibly there's a short which has dropped the regulated voltage too low, check 5V with a multimeter.

 

He rolling is just my budget iPhone trying to do video capture . I don't really want to be opening it for the 3rd time but I will post some pics tom...

 

Get a can of compressed air and give all the chips a blast around the legs, just in case.

 

Or just send it back to me and I'll fix it.

I'm 99% certain that there has been a break in one of the solder points where I put the switch wires in.

 

Ok just got this back.

Found some excess solder in between the legs of one of the chips. It's all clear now and I've totally stripped the whole system down. Cannot see any other problems, all caps seem fine but it's still doing it.

I too am testing with Streets of Rage and it's an awful sound but it's like Masterturk said, only sound effects seem to have the problem, the sound builds up and up and then just floods the speakers.

As far as I can see it might be the wires need resoldering on the mods but I've tested all regions and clock speeds and they work fine.

Really puzzled on this one.

EDIT update.

Does anyone know what the Cap which sits on the region/Hz solder points does? It's not on all models and I can't see for sure but it looks like I may have caught the underside of it with the iron and damaged it slightly. Doesn't look like it's leaked but the underside doesn't look too good.

It's the only thing I can find wrong on the board.

 

Play it for a bit and check if the YM2612 is getting too hot ...

 

Ep twimfy I recall whilst I was playing and when I decided to open it up the metal plate was hot are you referring to that?

 

The metal plate should be hot as it's dissipating excess of heat generated by the two 7805 chips. :thumbsup:

 

Ok here's what I've done so far.

Reflowed the solder on the Z80 and cart slot. Checked all capacitors, removed the mods and returned it to a stock PAL MD by bridging the broken traces.

Nothing has worked. I was speaking to TmEE over PM and he said it sounds like a cart slot/address problem as low memory games (such as Sonic 1) work flawlessly.

It's the Z80 that is having trouble as if I run Streets of Rage and then perform an action which forces the Z80 to take part, I can bridge the CLK on the chip and make the sound go away only for it to re-appear a little later.

Nothing is overheating.

I'm totally stumped, cannot think of a way to fix this at all.