Neo Geo MV-4 Repair

[xodaraP]

Hi guys,

I'm in desperate need of help to hopefully finish fixing my 4 slot MVS board so I'm hoping some experienced people might be able to chime in

Rather than post the full repair thread here from another site, I'll go through the tl;dr version

So far I have done:

Removed battery and resistor - battery had corroded traces
Replaced colour RAM (initial fault was a grey screen)
Replaced 32.768mhz. crystal (got as far as green screen of death)
Replaced heavily corroded LS05 (which tested bad off board)
Fixed 14 traces with jumpers (so far) on bottom board CN10 connector
Fixed 1 trace on top board (F174 at A1 was missing clock signal to pin 9, reconnected this to CN11 pin 22)

I am now getting as far as crosshatch of death. I've cleaned the cart connectors on the top board, confirmed that the F138 is healthy and everything else appears to be fine. I continued removing the 'foam' from the bottom of the board (it's completely petrified solid but it breaks apart if it's touched so it's a nightmare to remove) and I have found a resistor array in the area (marked as 10k x which is completely toast. Is this resistor array critical to the board booting the cartridges from the top board? I will replace it regardless but at this point I just want to get something to boot so if it's not absolutely necessary I'll continue to fix things like that after it's working at least partially again. I've put so many hours into this thing already I'd just like to see it done at this stage

Full thread is here if anyone would like to see the troubleshooting steps I've done so far (I know it's on another site but I'll bring it over here once it's a finished repair log hopefully)

https://forums.arcade-museum.com/showthread.php?p=3551846#post3551846

 

[Asayuki]

I have no idea where the resistive network you are talking about is placed, so can't answer that without more precise information.
But, as far as I remember, the bios will try and adress all slots one by one searching for an header in the P1 roms. If the header is found and satisfies the liking of the bios then program flow control is handed over to the P1 rom.
So you might want to concentrate on the signals that reach the program roms on the cart. Imho, chances are that you overlooked an acid-corroded trace which looks healthy but actually isn't.

 

[xodaraP]

I think I'll just try jumping the rest of the CN10 connector lines that were in the area regardless if they're reading as having continuity or not and see where that leaves me

The issue I'm running into is because I've had to replace so many I'm running out of space, and I'm worried about further issues being caused by possible cross talk of the wires.

The resistor pack is right next to the 32.768mhz crystal on the bottom board

 

[xodaraP]

I've resoldered all connections from the CN10 connector from A5/B5 to A12/B12 - the other connections are all fine. A couple of the ones I resoldered were reading fine, but I jumpered them anyway because the tracks were corroded and probably not working 100%

I have double, triple and quadruple checked all connections between my new jumpers and everything is now talking to the pin it should be talking to on the bottom board. I have double, triple and quadruple checked that all connections are making it to the top board.

At this point it still won't boot and I'm going to put it aside for now, I've done huge amounts of work on this board to even get it to this stage and it seems a shame to leave it here, but I just cannot get any further with it. The logic has all tested fine, I'm just not sure where to proceed from here. So for now, I will leave it here and perhaps return to triumphantly finish it at a later date.