So I recently got a Neo Geo and I realized pretty quickly that it has some graphical issues. Now when I received the board I noticed at some point in its life it had some repairs. Most noticeable was a bodge wire running from a via stitch to the work ram chip nearest to the battery there is also some light corrosion on that chips legs. Other issues included but now fixed, a cold broken solder joint to one of the back plane interconnects on the board, the pin looked like it had been completely disconnected. I removed the original battery but there was no signs of any bad corrosion or leaking. The last thing was a small scratch on about 4 traces and underneath the z80 it looks like the board delamintated a bit. Everything else looks fine.
The board is powered with a modded ATX power supply and the video is converted into VGA with one of those chinarific 18 dollar converter boards, lol.
There also appears to be a Sync issue but I am blaming that on the crappy video converter board.
Evidently I also have 2 authentic Neo Geo MVS carts. Metal Slug X (looks the worst) and Puzzle Bobble. I cleaned the contacts with 70% isopropyl. The cart edge connector on the MVS main board looks to be fine. The sound is good to as far as I can tell.
But by this point I am at a bit of a loss as to where to start. I dont have a logic probe (yet at least) and though I think the culprit might be the Work Ram chip, I am not sure. I also cant rule out 20+ year old caps.
Forum I need your help with this one, its going out side my realm of expertise.
That particular problem is caused by "lost pixels". Let me explain.
By the center of the board near the white connector there's a 74LS32 chip and the NEO-ZMC2 custom IC. The NEO-ZMC2 is the "pixel serializer" for the sprites ROMs (C-ROMs) and what it does is convert 32bits of data (the NEO always access C-ROMs in pairs and each chip is 16-bit) into two 8bit multiplexed buses which are then fed to the NEO-B1 chip which in turn generates the video using that data from the C-ROMs and FIX (S1) ROM. If timing problems happen, the latches inside the ZMC2 chip might lose data at the inputs and that reflects at the output (which is what get sent to NEO-B1 and ends at the screen as sprites).
There are a couple of jumpers between the ZMC2 and the 74LS32 chip. What those jumpers do is change how much delay is added to the ZMC2 chip. You could try opening J5 and closing J6 to see if that helps out.
If tweaking the jumpers doesn't help you might want to check the traces around the ZMC2 chip and eventually consider replacing it.
So I went in and cut the trace to J5 with an exacto knife and bridged the two jumper pads on J6 with solder but no real change. Would playing with the other jumpers help?? Also I went ahead and checked the traces around the ZMC2 chip but I dont see any real damage. I would rather not pay for a second donor board and replace that chip hmmm
(edit) I might make a new thread for this since it might devolve into a general repair/mod log of sorts havent decided though
So an update for people looking at this;
This board had ended up being a real bother, after tracing all the pins from the ZMC2 to their locations, changing the jumpers, I found no change.
Now this board did have some issues like i mentioned, at some point someone repaired a trace by the battery, and replaced the Z80, when they replaced the Z80 it caused utter chaos to that part of the board!!! The board delaminated some and the backplane connector to the cartridge sub board has sustained heat damage in the form of warping. I noticed a Via missing under that Z80, I wanted to investigate it but It seemed unrelated to the core issue so i ignored it for the time being.
I ended up just buying an Untested MV1 on ebay for 25$, the board was in fantastic shape but it gave a Work Ram error. After swapping the 2 Work Rams out with the ones on the first MVS i had, the new board instantly came to life !!!
And now I return to this board now, the one I got ripped off on, to repair it and either flip it or consolize it.
The first order of business was to pull the Z80 out and see just how bad the damage was. After removing the Z80 and cleaning the area up, I tested all the other traces and vias which were fine. The missing via seemed to shift to the component side of the board lifting out of the board with the trace about 1mm or so
So I have since repaired that destroyed trace where the via once was and I also put a 40pin socket at the z80. I never want to pull that chip out again, aside from the fear of ruining that area more from heat it was a pain in the butt to remove it so sadly i had to clip it out poor z80.
ALSO!!!! Here are the notes and pin outs from the ZMC2 chip and various other chips related in case someone needs this for a MV-1FSB. Thank you Oliveira from the chat room for the guidance!!
ZMC2 Pin/Trace check.
Tested all continuity from the ZMC2 chip pins to their final destination.
So I started messing with this board again, I fixed the z80 error I was getting due to a damaged trace during the socketing of the new z80 (so much heat damage from some previous owner) and repaired another trace somewhere else on the board I later found but that trace was not the culprit.
I really need to find a cheap alternative way to find a ZMC2 I hear you can get one off of an AES cart but broken ones are far and few to find and buying a donor board just for the chip is a bit over kill. Does anyone have a cheap AES cart or has a ZMC2 chip they can part out to me. I really want to save this board :/ Thanks
The issue was finally solved by replacing the Cartridge connector board. Even though it looked fine and the board and contacts were cleaned NUMEROUS times. Something is wrong with it. Maybe a cold solder joint or broken contact?? ill have to recondition it.
Now off to fix the next 3
I checked continutity to from the ZMC2 to the back plane connector pins on the main board and other components, maybe i should have checked all the way to the pins on the cart connector.
Also just fixed another neo geo board with a z80 error because the SM1 chip has 3 cold solder joints
The board delaminated some and the backplane connector to the cartridge sub board has sustained heat damage in the form of warping. I noticed a Via missing under that Z80, I wanted to investigate it but It seemed unrelated to the core issue so i ignored it for the time being. 
poor z80.
