NeoGeo MVS Video Problem (Channelmaniac ?)

[CheffoJeffo]

Last night, my MVS-2-25 started showing some signs of video corruption. For some graphics, every second column is blacked out. Happens with all carts in both slots. Colour test comes up fine, as do many of the graphics. I was thinking RAM issue, but am not really sure where to start.

I have verified the voltages at the board and quickly checked the voltage drops across the 5814 RAMs and 74LS273Ns without finding anything obvious (but I was just looking for an obviously strange voltage drop). I also checked the resistors and everything appears good. I reflowed the cart connectors as well as the connections for the 5814s and LS273s, just in case. No change.

I guess it is time to grab a schematic and check traces.

Any suggestions as to where to start ?

Thanks.

[Malenko]

clean all the contacts. I had the exact same problem and once I cleaned both cart edge connectors and all my carts the problem went away. Im not  saying this will fix your problem, just what fixed mine.

[CheffoJeffo]

Thanks. Yeah, I should have mentioned that all contacts and connectors have been thoroughly cleaned.

[CheffoJeffo]

Seems that there aren't any schematics available, but I am working through channelmaniac's excellent posts on Neo-Geo.com, particularly this one:

Troubleshooting MVS 2F Video Problems

Also found an interesting thread highlighting the locations of the various RAM on the various MVS boards (also added to the restoration page in the wiki).

[Malenko]

worst case, I have a 2 slot collecting dust in my closet.....

[CheffoJeffo]

I may take you up on that, thanks.

Ran the board on the bench for most of the day with the logic probe and didn't find anything stuck.

Haven't found any broken traces (working backwards from the harness, through the resistor ladder, through the latches, etc.) or cold solder joints.

Haven't made a damned bit of progress.

On the plus side, I did get my MultiJamma working again today (water damage to CP, controls, PS ... apparently not boards, though).

SurfPlanet ftw!

[channelmaniac]

Hmmm...

If you have a logic probe you can track it down by process of elimination.

The NEO-257 IC is a few 74LS257 2 to 1 data selector ICs in one package. They are used to select which slot to get the graphic data from. You can find the pinouts in my repair logs. I figured out the pinouts for them and have posted them there.

Take your logic probe and check the inputs to the 257 IC. If you find an input that looks "odd" or is missing (in other words, stuck high or low) then check for a bad trace between the 257 and the slot or check for a dirty/corroded slot or a dirty/bad cart.

If the input is in a "race" condition and the trace is OK then the input is probably bad on the 257 IC.

I know you said you cleaned the cart connectors but look with a magnifying glass if it points back to a bad trace. If there is corrosion on the connector the cleaning won't help. You'll have to scrape the corrosion off with a small jeweler's screwdriver or with a point burnishing tool. (Available at any automotive parts store)

If you have inputs but no outputs on one of the data lines on the 257 IC then replace it.

If the outputs are good then check the traces between the 257 IC and the ZMC2. Bad traces are common here from leaking batteries. If the traces are good and you get the signals into the ZMC2 then replace the ZMC2. But, I have to tell you, that is a RARE IC to have to replace. It generally just doesn't go bad.

I find that the easiest and best way to clean the slots is to use Formula 409 Orange cleaner and a tooth brush. Rinse VERY well with distilled water, alcohol, or tap water if your tap water has a low mineral content.

If you need the NEO-257 IC replaced let me know. I do all Neo Geo repairs as flat rate plus shipping.

Raymond

[channelmaniac]

I keep all Neo Geo related repair logs in a single thread on my repair logs section at the NewLifeGames.net forum.

Here's the pinout for the ZMC2:

http://newlifegames.net/nlg/index.php?topic=152.msg906#msg906

Pinout for the NEO-257 by connection to other chips:

http://newlifegames.net/nlg/index.php?topic=152.msg909#msg909

Pinout for the NEO-257 by function:

http://newlifegames.net/nlg/index.php?topic=152.msg910#msg910

Enjoy!

[CheffoJeffo]

Thanks channelmaniac!

I probably won't get back to it until Wednesday night, but now I have something else to look at.