Audio problem on MVS 4F - Slot 2 no sound and will take out other slots if cycled through

ledfrog

n00b
Joined
Mar 9, 2017
Posts
42
I'm new to the Neo-Geo ownership scene after picking up a cabinet at auction so my apologies if this issue has been discussed before, but all I could find was people having sound issues or no sound on all slots at once.

The system was playing ok at first...I had some glitches and sound issues on all slots, but fixed the glitching by a good cleaning of everything. The original sound issues were fixed by a fresh cap kit.

One problem that seemed random at first was the sound in slot 2. Sometimes it worked and other times, when it played the first sound of whatever game I put in there, it would shoot out a Z80 error. Now, I get absolutely no sounds in slot 2. The most interesting part is that the system starts up on slot 1 and the sounds and gameplay are perfect, but if I cycle through to slot 2, the sound stops and the game plays great. BUT when I switch to slot 3 and 4 and back to slot 1, the sounds are still dead. They never come back on in any way until I power down the system.

If I leave slot 2 empty, I can cycle through all the other slots and all the games play perfectly with all sounds in tact. It's obvious at this point that slot 2 is the issue, but I'm not too versed in the schematics of this board to know where to look.

Here's what I've done:

  • Complete cap kit (fixed low volume and some static issues)
  • Checked for obvious bad traces
  • Checked continuity on the pins inside slot 2 and matched the results with other working slots (it seems slots 1 and 2 are paired as are slots 3 and 4)
  • Cleaned all slots and game cartridges using 91% isopropyl alcohol and again with a pencil eraser
  • Cleared backup ram

The last bit of info I'll point out because I think it might be important is that there is one LS245 chip on the board that someone before me has modded to include a connection between the ground pin (pin 10) to a closeby ground trace. If I remove this link, the sounds are garbled and messed up. It appears that this chip for some reason does not ground properly in its socket. From what I can tell, there are no other mods on this board.

Ultimately, what I'd like to know is what set of chips are used to control each slot? I know schematics for these boards are non-existent so I'm wondering if anyone knows that path from each slot to the sound area of the board. I'm led to believe that these slots act somewhat independently from each other given that I have sound in 3 of the 4 slots. Any help would be greatly appreciated!!! I can send pics if anyone wants to see something specific.
 
Last edited:

pulstar

Mickey's Coach
10 Year Member
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Jun 6, 2011
Posts
578
Have you tried the same game only in slot 2 or have you tried different carts? What happens if you fill up slot 1-3? The same error?
 

ledfrog

n00b
Joined
Mar 9, 2017
Posts
42
If I only put one game in slot 2, it plays great but without sound. Also, it doesn't matter what game is in slot 2...I've tried 6 different cartridges and they are all missing sound. If I put games in slots 1, 2 and 3, it has the same effect as putting games in all 4 slots; as soon as I cycle to slot 2, it kills all sound for all slots until the system is powered off and back on again. The only way I can get a functional MVS system is to leave slot 2 completely empty. :(

On a related note, I haven't seen a Z80 error in a couple weeks. From what I remember, there was a time when slot 2 had a slight bit of sound, but it would usually cut out around the title screen of whatever game was inserted. Sometimes the sound would just go and the game would continue playing...other times it would show a Z80 error. At this point, no other slots are giving me any trouble.
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,923
I think it was the backup ram. Generally if you load a game when it's not connecting properly, you can save errors into the backup ram. I would re-seat the game and clear the backup ram when running into these issues.
 

ledfrog

n00b
Joined
Mar 9, 2017
Posts
42
I think you hit the nail on the head! I was actually going to do what you suggested, but my new Universe BIOS 3.3 came in the mail today and I decided to install it first. Part of the installation process is that the SRAM is cleared to "ensure compatibility" and sure enough, all four slots are now working perfectly! I guess after I cleaned all my games and the slots, I failed to remove the saved errors.
 

sr20det510

Guerilla Warrior
Joined
Oct 31, 2016
Posts
1,730
I see you are Long Beach, any chance you can recap my 4 slot?
I have the low sound issue.
 

NEO G-TRON

Marked Wolf
Joined
Mar 15, 2004
Posts
212
Glad to see you figured out your mobos issues. Time to enjoy! I'm located in Downey and host Neo Geo/retro gaming gatherings If any of you two are interested in checking then out sometime. Pico's my neighboringredients city and the LB is also nearby.
 

sr20det510

Guerilla Warrior
Joined
Oct 31, 2016
Posts
1,730
Glad to see you figured out your mobos issues. Time to enjoy! I'm located in Downey and host Neo Geo/retro gaming gatherings If any of you two are interested in checking then out sometime. Pico's my neighboringredients city and the LB is also nearby.

Orale, sounds like a plan Neo G-Tron.
I actually drive through Downey every weekday.
 

ledfrog

n00b
Joined
Mar 9, 2017
Posts
42
Glad to see you figured out your mobos issues. Time to enjoy! I'm located in Downey and host Neo Geo/retro gaming gatherings If any of you two are interested in checking then out sometime. Pico's my neighboringredients city and the LB is also nearby.

Sounds like fun...do you have some sort of mailing list to get on for event notifications?
 

ledfrog

n00b
Joined
Mar 9, 2017
Posts
42
I have to add that my sound problem had come back the other day and I discovered another issue that easily resolved. When I took the cartridge out of slot 3, I noticed that some of the pins were stuck and weren't make connection to the game. To better illustrate this, when you push on the pins, there's a spring to them which keeps a tight squeeze on the game. Some of my pins don't spring back so I had to pull them forward. It appears the issue happens if I put a cart in and rock it back a bit...it pushed the few pins back and they never bounced back to touch the cart again.

I may invest in replacement slots OR just put a game in and leave it!
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,923
Yeah, the tension of the slots is really important, and fragile. Don't mess with it.
 

ledfrog

n00b
Joined
Mar 9, 2017
Posts
42
I finally picked up some replacement slots for my 4-slot board. It wasn't that easy to remove the original slot from the board, but the end result was well worth it!! I was able to secure a pair from a member over on KLOV, but since I only had one problematic slot, I only replaced one. It worked out since I now have a spare for future use. But anyway, I wanted to report back for future searching of this issue in case someone else has the same problem and has ruled out all other possible fixes. If you inspect the pins in each slot closely, you'll want to make sure that none of the pins are stuck in the back position. In my case, every time I removed a cartridge, I had to manually push a couple of pins forward in order to make contact for the next game. As long as nothing was touched at this point, my 4-slot board played perfectly. As soon as I swapped cartridges from the bad slot, I would have to push the pins back again...or I'd have missing audio on every game after it in the rotation.

Here's a picture of my defective slot highlighting all the potentially bad pins. Despite the fact that I have 9 pins marked in this photo, I really only had to mess with about 3 of them. The NOS replacement that I installed had perfectly aligned pins and my problems are now history!
4slot-pins.png
 
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