2 broken SNK MVH MV1-1 boards! Need help repairing several damage and fix them!

[ftadeufs]

Hi guys, this is my first post here in this forum.
I´ve read a lot over the internet during the past weeks trying to solve my problems, and decided to register here, because this was the best forum I´ve found.


I live in Portugal, and I´ve found a pair of arcade cabinets at good price with several damage to the monitors and game PCBs due to rodent and bird dejections on the past 20 years…  . I´ve fixed both monitors, and sold one cabinet.


Now I have a working jamma cabinet, and two SNK MV1-1 Boards both with serious damage due to battery leak and animal cohabitation .


So, I decided to clean everything and test the boards again to try to repair them. They are both crazy as expected from the visible damage…
I have some experience regarding electronics repairs and finding faulty components, so I already tested the monitor for good and the power supply is working fine and clean. I have a pandora´s box for testing arcade machines and it works flawlessly on this cabinet, but I dont like it. The ideal solution would be to repair the two boards, and sell one.  If not possible, repair one and save another for spare parts.


But here is what I´ve already done to the boards:
Replace all 470uF16v. caps, because they were measuring 250uF capacitance.
Replace all 100uF caps,
Cleaned all battery leak damage with IPA.
Fixed all visible bad traces, and continuity tested everything found broken on the two boards.


Now I dont know what else to do, because everything I tested is OK, and I don´t find any more broken traces. I have a small DIY oscilloscope (DSO138) but I dont know what to look for in the TTL comunication, and I dont know if I can use it to test logic circuits.


So, the behaviour is like this at the moment:
Board 1: Does lots of green garbage on the screen, flickers and clicks like the watchdog symptom, but if I let it on for a while (2or3 min) it stops reseting and shows fixed green trashy squares on the screen. Same happens if I remove the bios Chip. Bios chip makes no difference in this problem.

If I pass my finger gently on the top of some RAM chips it influences the garbage on the screen. Nothing is getting minimally hot, except for the YM2610.

Board 2: Boots to weird text like:
IIEE AA RROO
DDRRSS   IIEERRAADD
00000022  5555     5500
Sometimes, if i let it on for a while, it starts to show white garbage on the screen… If I pass my finger gently on the top of ZMC2 ic it influences the garbage on the screen. If I tap in it with something plastic it has no effect.

Some chips get a little warm but the warmest is the YM2610.

All this tested with no game inserted. I have a world heroes 2 cartridge that I tested on a Four slot MVH and it works fine!

I tried flexing the board, or pressing on the chips, but nothing changed.

I want to fix this boards, first of all because I can´t stand the idea of trashing this awesome systems. And I love to fix stuff and want to learn as much as I can about electronics, specially repairing old classic games machines to keep them running. Home consoles and arcades. Bringing these old things back to life gives me a lot of joy.


I´ve read a lot of repair logs from "channelmaniac" but I didn´t find any matching this descriptions.


Is there any schematics on these systems that shows what continuity should be between all pins of all chips? I cant find schematics for this model.
Is there any signal I can measure with my DIY oscilloscope or multimeter to track down the problem?


I will try to make pictures or videos of both problems on both boards and post it here if needed.


Thanks for any help, and I´m sorry if some parts of my english are weird.
 


EDIT:
Here are some pictures in attachment.


Video of the first board here:
https://youtu.be/pmfjtrPJqmY


Thanks

 

[alfa75]

I would use a universe bios at your place and then run a diagnostic on it.

[Josh128]

Yeah, use the Uni BIOS or flash a diag BIOS and try that.
The address that its displaying seems to be corrupted.  D0006x falls into an undocumented area  in the neo geo dev wiki, so... not much help there.  Definitely a RAM error occuring, which RAM is the question.