MVS MV1FZSB-2 Z80 Error / Strange Audio

[funk]

Had this working before but something seems to have happened recently.

Board boots with the infamous Z80 error, regardless of cart.

Swap the bios out for a unibios 4 and I can get games to boot, gfx and controls are fine but weirdly, some, only some of the audio is slowed down, or played at the wrong times.

E.g. Win, loose jingle in puzzle bobble is fine but the music that's playing during play is probably playing 10th to 20th it's normal speed. The intro of metal slug one plays but with some different sounds for each of the noises.

Same carts play flawlessly in another board. Logging it so I don't forget where I'm up to with it!

 

[TheDaddy]

Yeh very common on these. Has the battery been replaced ?? Has it leaked ?? That is the most common fault as it eats the tracks away. Failing that it could be the ram, TRack or Z80. Been a while since I did one though.

Hope this helps,

Dave.

 

[Flinnster]

Yep sadly this is a bad sign.
Even boards with batteries removed, the corrosion can creep along the tracks under the yamaha audio chip at the back right of the board, or under the Z80 and RAM near where the cell battery is. The connections required from these chips go to multiple places including the BIOS chip and along the back of the board.
Testing them all individually against a known working board is the main way I've repaired these, adding in patch wires where needed. Ideally, you'd want to clean everything with vinegar to reduce the chances of lingering corrosion continuing under the chips etc..

 

[funk]

Weirdly the battery wasn't in amazing shape but hadn't really leaked. I'm yet to get hot air out to remove the gunky thermo pad underneath that area though.

 

[funk]

So it's a blessing and a curse this board was faulty as it's partially working with a unibios in it, will be a good little project to get me uses to the logic probes etc.

Exhausted my time this weekend, which was spent removing that sticky foam from the backup memory area - what a nightmare and drinker of IPA, worst than me down the local!

The good news is, doesn't look like it's leaked, separated the slot board, gave that a good clean too so it's all just drying off now. No hugely visible traces or pins damaged aside from one capacitor which I think is a smoothing jobby, and that was missing when I got this one, before it failed.

The fact that the notes are playing, but slow on the puzzle bobble music makes me think whatever clocks that channel is stuck or triggering at the wrong point in time.

Whack slug in though and the.sounds are playing out of order, making me thing something could just be stuck high, triggering the register to play the wrong sound.

One for next week maybe, but finding what things should be doing is difficult given not having a dupe of this board, and not easily being able to probe with a cart in. My other boards are typically different varieties.

 

[grobda]

Had a MV1-B that was giving Z80 error. Replaced the 6116 ram and it worked for a while then got more z80 errors. Had a scrap MVS with severe gouging to the underside of the PCB so snagged the Z80 off that which fixed the problem. Not used to surface mount components but it wasn't too bad replacing it using a bit of low temp solder paste. I did read somewhere that surface mount Z80's on MVS boards have a high failure rate.