Metal Slug 3 CHAFIO woes

Joined
Jun 14, 2012
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10
Yet another problematic CHAFIO scrambled graphics thread. I've seen these previous Metal Slug 3 and Nightmare in the Dark threads.
http://www.neo-geo.com/forums/showt...k-Glitchy-Scrambled-Graphics&highlight=CHAFIO
http://www.neo-geo.com/forums/showthread.php?267831-Problem-with-Metal-Slug-3-MVS&highlight=CHAFIO

My CHAFIO scrambled graphics misadventure started 5 years ago with a trip to Japan. Found a wonderful deal on a very much used MVS Metal Slug 3 in Akihabara. It was not super pretty and had obviously been opened before, but it was cheap, a game I wanted, and a great souvenir. Here's the condensed story of the aftermath:

1. Cleaned it thoroughly, but it had corrupt graphics from day 1. Cleaned it again, and the graphics corruption went away ---- for only a month.

2. Opened it up. Cleaned CHAFIO again.
No luck. Goofed around with bare boards in the MVS (being of course dilligent about board order and orientation!) Noticed mechanical pressure on one of the C ROMs cleared it up briefly, so I assumed there was a bad solder joint. Reflowed that particular C ROM, and the game was perfect! For a month.

3. Opened it up again and this time reflowed all 8 C-ROMs. Actually tried to remove one and test it with my Batronix Batego 2, but I could never get more than half of the data out because there's no 64 megabit chip setting in the Batronix recognized chip repertoire (32 megabit was the closest I could get). In any event, the 32 megabits it read out seemed OK.
After replacing and reflowing all 8 C-ROMs, the game played perfectly. This time for 3 months.

4. Today I decided to work on it again, this time removing and testing M1 EPROM, which I should have done in the first place because it's only 4-megabit. However, the M1 EPROM tests fine, and replacing it with new solder made no difference.

5. I have also done continuity tests across all 8 C-ROMs (address, data, etc.) and they SEEM fine, at least on my workbench. Similarly did my best to continuity check between the NEO-CMC and C-ROM and M1-EPROM, as well as between the cartridge pins and surface mount resistors and NEO-CMC. This also seems OK on my workbench. That said, every now and then applying mechanical pressure (i.e. pull out the CHAFIO board, pinch something, reinsert it and test again) can change the corruption pattern seen, but I cannot identify a particular area causing the problem.

So obviously anything faulty in the entire CHAFIO board can cause highly visible corruption because every component in the board is used for descrambling the tile data. I think I've ruled out M1 for now. And although I cannot prove it, I'm inclined to believe the C-ROM silicon is OK (or else it never would have worked cleanly at all).
But between C-ROM silicon and NEO-CMC silicon we have:
a) wire-bond to DIP package lead frame
b) board traces
c) board vias
d) wire-bond from NEO-CMC QFP lead frame to silicon.
And there are also
e) surface mount decoupling capacitors and resistors. Certainly a bad solder joint on a decoupling cap could cause havoc on this board by injecting noise.

Ideas?

One thought is to reflow the entire PCB, in case any surface-mount solder is bad. As someone pointed out, there's a huge ground plane acting as heat sink on this board. I wonder how good the solder was out of the factory?

Not every via has a solder plug either. Shouldn't be a problem unless a via is broken.

Another thought is to try to make it worse --- use freeze spray to try to isolate bad joints. Still not an easy task.

Has anyone ever scoped the power rails near the NEO-CMC to see if they are noisy? I wasn't sure if 4 decoupling caps (one on each side) is enough for the CMC?
 
Joined
Jun 14, 2012
Posts
10
I tried filling in some empty vias (mostly near the cartridge pins) in the off chance of a cracked via. It had no effect.
I rechecked continuity test on the bench across all C-ROMs and NEO-CMC, and again all looked good.

I once again seated the naked PCBs directly into the system, and subsequently observed that a little pressure on the edges of the PCB corners near the C-ROMs fixed the graphics.
I was able to play through Metal Slug 3, with corruption returning 3 times and the same gentle nudge fixing it every time.

So once again I conclude the chips are all fine, at least at silicon-level, and I must have a very intermittent trace/bond/via somewhere I'm not seeing on the bench.
 

Neogeoman106st

Crossed Swords Squire
Joined
Aug 29, 2017
Posts
191
if pushing down on the PCB while in the MVS fixes the issue for a short time. It sounds like you might have a motherboard Slot problem and not an issue with the game. Have you checked and cleaned the MVS motherboard game slot? Checked for some bent pins etc? if not i would take a line cloth, a card and isopropyl alcohol to give it a good cleaning.
 
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Joined
Jun 14, 2012
Posts
10
No, it's definitely not a slot problem. The problem followed the cartridge, not the slot.
However, I think it's finally fixed for real now.

I took the board under a good lens and realized there were large deposits of flux between the NEO-CMC pins.
This wasn't my doing, so it either came that way from the factory or, given the history of this el-cheapo cartridge, someone else in Tokyo did it.
Furthermore, lodged inside this flux were several super tiny solder blobs. Bingo! Again, not my doing. One wonders if someone made a NEO-CMC transplant in the past?

I suspect this was the source of the mechanical stress temporarily fixing the problem. Intermittent unbridging between those fine-pitch NEO-CMC leads.
I cleaned it all out and haven't had the problem since. :-)
 

GadgetUK

Ace Ghost Pilot
Joined
Sep 27, 2013
Posts
1,323
Good information there! I had a "flux" problem like that on a Puzzle Bobble (original) cart. Flux between two pins causes speckles all over the display and like you found, I could make it better or worse by manipulating the board.
 

Hawwa

B. Jenet's Firstmate
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Sep 21, 2018
Posts
408
I've been having similar issues with a KOF '99. Contacts are clean (alcohol + eraser) and the boards seem to be in perfect condition as well but I have the issues showing on this video


As you can see text is OK and some stuff here and there as well (fighter icon, life bar, etc.)

I've tried cleaning the CMC with a tootbrush and a spray duster and still the same behaviour.

Any ideas what else may I try?
 

Neogeoman106st

Crossed Swords Squire
Joined
Aug 29, 2017
Posts
191
I've been having similar issues with a KOF '99. Contacts are clean (alcohol + eraser) and the boards seem to be in perfect condition as well but I have the issues showing on this video


As you can see text is OK and some stuff here and there as well (fighter icon, life bar, etc.)

I've tried cleaning the CMC with a tootbrush and a spray duster and still the same behaviour.

Any ideas what else may I try?

its amazing what one can find with a quick search https://wiki.neogeodev.org/index.php?title=Graphic_glitches

based on the above link you ,might have an issue with the LO rom data. take a good look at the site and maybe reflow some of the Rom chips to eliminate cold solider joints.
 
Last edited:

Hawwa

B. Jenet's Firstmate
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Sep 21, 2018
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408
Am I wrong or ain't the LO ROM in the motherboard?
 

defalt

Cheng's Errand Boy
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Oct 12, 2017
Posts
114
It is. On your video the S ROM is good, the C ROMs are not, but if other games work fine the problem has nothing to do with the L0 ROM. If so, your problem comes either from a cut trace near the C ROMs or a NEO-CMC problem. I have plenty of NEO-CMC 7050s if you want, but iirc KoF 99 uses a 7042.
 
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Hawwa

B. Jenet's Firstmate
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Sep 21, 2018
Posts
408
Thanks for the reply. Yes, every other game works flawlessly on this systen so it has to be cartridge related.

I'll check the traces but if they are ok and this cartridge needs a new CMC, that is beyond my skills (by far).
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
With the CMC the problems are usually floating pins that need to be reflowed of internal failure, usually you will see a crack on the CMC if there's internal failure. C-roms contain both normal C-rom and S-rom data or I should say that the S-rom just got merged with C rom data. M1 is for sound program only.
 

Hawwa

B. Jenet's Firstmate
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Thanks for the reply. I've checked again with a magnifying glass and I can't see anything broken or not properly soldered. PCB's seems completely fine. Here you are some pics. If I can't find a solution to this I'm thinking of giving the cartridge out for free to anyone who thinks (and wants) may fix it (for them to keep, obviously).









 

BIG BEAR

SHOCKbox Developer,
20 Year Member
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Dec 14, 2001
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8,230
If you ever want to sell it for cheap lmk.
BB
Thanks for the reply. I've checked again with a magnifying glass and I can't see anything broken or not properly soldered. PCB's seems completely fine. Here you are some pics. If I can't find a solution to this I'm thinking of giving the cartridge out for free to anyone who thinks (and wants) may fix it (for them to keep, obviously).
 

Hawwa

B. Jenet's Firstmate
Joined
Sep 21, 2018
Posts
408
If you ever want to sell it for cheap lmk.
BB

For users like you it's at no cost. Just the shipping. You can PM with your details and I'll ship it to you since I don't think I'll be able to fix it.
 
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