MVS Schematics

jacklinks

Timid Neo Newbie
Joined
Nov 15, 2022
Posts
4
Hey all, brand new member to the forum here. Looking for help and advice on various NG projects and hopefully share some of the things i've learnt myself.

I've currently got a sound issue on my MVS 6 Slot.

If I put carts in slots 1, 3, 4, 5, & 6 I can cycle through with no problems no matter what the order and the sound is all good.

As soon as I introduce any cart to slot 2 the sound goes out as soon as I cycle to slot 2 and wont come back unless I reboot the machine.

So it will boot up to slot 1 with the sound, i cycle to slot 2 and theres no longer any sound then I have no sound on all slots when cycling until the machine is turned off and on again.

This happens regardless of which carts are in which slots and always the problem comes when using slot 2.

I've cleaned all slots carefully and all carts with deoxit and isopropyl and no change.

I've also tried the original BIOS, Unibios 3.3 and Unibios 4.0 which don't solve the issue.

I've slowly gone up and down 0.01v at a time between 4.9 and 5.2v on the PSU and no dice.

Any ideas would be great thank you!
 

SignOfZeta

Butthurt Enthusiast
20 Year Member
Joined
Sep 18, 2003
Posts
2,410
I loved your post. This is only because the question wasn’t about a multicart or flash cart. No other reason. I don’t have any other advice, sorry.
 

jacklinks

Timid Neo Newbie
Joined
Nov 15, 2022
Posts
4
This is likely the best you are going to get for 6 slot info


Based on what you describe it sounds like the z80 is crashing when switching to slot 2. There is probably some z80 data/address issue going on with that slot. The bottom of that wiki page talks about z80 data/address lines.
Thanks for the advice man. I'm a bit green but wouldn't the Z80 crashing take out the video aswell? It's only the sound that goes out when I pass through slot 2 but the video and game itself play perfectly fine otherwise.

Also when I run the diagnostic check using a Diagnostic BIOS chip, it all comes up as 'ALL TESTS PASSED'
 

ack

Fio's Quartermaster
10 Year Member
Joined
Apr 9, 2009
Posts
481
The neo geo has 2 cpus. A motorola 68000 which is the main cpu, and the z80 that handles sound. So when the z80 crashes its going to take out sound.

The diag bios requires the m1 rom / cart to support testing the z80 cpu.
 

jacklinks

Timid Neo Newbie
Joined
Nov 15, 2022
Posts
4
Ah that makes perfect sense. Thanks for clearing that up for me.

Is there a list of games/carts that have the M1 ROM? Or do I need a flash cart?
 

Neo Alec

King of Spammers
20 Year Member
Joined
Dec 7, 2000
Posts
10,278
Yep, that's what I mean. You should just need to hit the buttons on that screen and it will confirm cleared.

Sadly, I love this old hardware, but agree with ack that these boards are considered to be very tempermental, and it sounds like you got a pretty decently-working one.

It's probably worth checking all the lines from that slot, but those cart lines can be hard to trace back.

You need to make a special cart for the diag bios M1 rom.

From your post, I assume you've tried shuffling different carts around to different slots. Carts from different eras with different hardware on them are known to not always play nice on multi slots. I would try putting 6 early games in there with no encryption or copy protection on them, if you have them, to prove definitively the slot is the problem.
 

maki

Krauser's Shoe Shiner
Joined
Jan 1, 2022
Posts
231
@jacklinks
as other said, the 6 Slot MVS is quite complex and tends to have problems, simply because of its complexity.

If you don't bother fixing it, 5 slot would still work the way I understand it.

I strongly suggest to get rid of the old battery, they tend to leak and that corrodes lots of important ICs and traces, as long as the old battery is in there, it will get worse IMO

clean the area with white vinegar (to deactivate the acid form the battery), then clean that off
try to fix/clean the PCB as much as possible

tbh, starting to fix 6 slots is quite hard, single slots are much easier, easiest is the AES (least complexity).
 
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