NEO GEO MVS 4 SLOT Currupt Graphics / Battery leak Repair

Ok I'm currently in the process of bringing some Neo Geo MVS boards back to life, i have a 6 Slot that had harsh battery damage, wasn't booting. And a 4 Slot which this thread is about.

Thought I'd document it here for anyone else looking for help with similar issues.

The board arrived this morning, it wasn't packed great, newspaper was used, so the board has a little damage around the edges, nothing serious no components or traces damaged etc

Just one of the black edge connectors and one corner where a PCB mount was.

anyway This is what it does:



Looks like it's got some battery leaking / corrosion, so i'll clean that up first.
and see what happens.



Seems better layout than the 6 slot around the battery area, less chips but more traces which look pretty ropey lol. fun times ahead.

 

Looks like your battery leak isn't too severe. Double check the traces are OK. Then get the logic probe out!

 

it's not too bad, at least this one boots lol, the 6 slot on the other hand is a pain in the ass, still getting "B240" even after changing the C1815 transistor grrrr.

 

Uhh, have you checked the RAM?

Why did you change the transistor? Was it faulty? I know there have been reports of that being the issue, but you really need to fault-find first, not just change a component because it worked for someone else. Always check a component IS faulty before you change it - it'll save time and money!

 

i changed it due to the corrosion from the battery leakage i didn't bother testing it as i planned on changing it anyway.
i've went over the 6 slot a few times now checking the traces and components etc. everything seems fine, i have yet to check the actual ram chips i'll do that soon but at the mo i'm rockin on with this 4 slot, and getting ready for a wedding

 

Certainly check logic in both cases. Starting with this one is probably going to be the least headache, yeah!

 

See that ZMC2 chip ? It takes 32 bits of data lines from the graphics ROM and multiplexes into 8 serial lines which go to the B1 chip. Look that the corner of the board are broken, goes exactly to the ZMC2 chip. So that's the graphics lines. You have traces broken there which need mending.

 

It's the C ROM address lines ("P0-P23"), not the ZMC2--the data looks fine. It could be traces or damaged buffers.

 

The damage in the board is not near any traces that go to the ZMC2 nor anywhere else, it does not reach anything, i've double checked the ZMC2 pins just to make sure none were lifted from the board.

indeed the data is fine and all there, just seems to be weirdly in the wrong order, eg the outside lines are on the inside, foreground sprites and text seem to be fine, whereas the background and player sprites are whats not right. this is the same no matter what slot is used 1-4 so i dont think it's the top board at fault.

 

Well I was saying that because the DATA and ADDRESS lines for the C bus aways travel nearby.

You might want to test carts on the 4 slots as one of the buffers could be fubar and not affecting the other slots.

A oscilloscope or probe would help you greatly.

 

The top board probably is at fault; IIRC the P lines go through a buffer driving all 4 slots. It's a low address line, probably between P0 and P9 (A3-7, B3-7).