Neo Geo MVS not booting, any ideas?

Video of what im getting on screen

 

Broken traces are preventing the 68000 CPU from starting. The CPU watchdog circuit (on the graphics chip) detects there's no CPU activity and keeps kicking reset which makes the screen "jump" periodically.

 

Edit: Thanks for reply l_oliveira - please excuse my lack of knowledge this is my first neo geo hardware

That explains the jumping, an update i've lifted some ICs around the battery leakage area and well one fell apart lol, no visible trace damage around the 68000 area.

chips i removed were the HD74LS05P's and a DM74AS244N, D4990AC(calander clock chip i think) and a 74HC32P this may be ok but the solder around one of the legs was badly corroded and a trace lifted with the pin, but should be easy to jump, also a NEC chip (uPA2003C) but i think thats ok.

hopefully it's just an elusive broken trace as you say but as of yet not found.

I'm Determined to bring this board back to life, i'll be ordering up some new chips and some flux on friday

on the bottom of the top board there's a very fine trace that looks suspect too around one of the 4 edge connectors(that connect the two boards) so i'll get that sorted too.

Question:

1 other thing, if anyone knows, There is a JP1 connector on the Top board but just a place for it on the bottom board with no connector soldered on, i know this is to supply power to the top board but was only used in early models? info is sketchy but im not sure if i need this to be hooked up or not (eg someone may have de-soldered connector from bottom board or it may never have been there from factory)

 

There's two jumpers on NEO GEO boards which have fixed function:

JP1: Causes CPU pin /BERR (BUS ERROR) to be held low
JP2: Disables the CPU watchdog

That 74HC32 is part of the backup memory watchdog and since it controls the chip enables for the two 62256 SRAM chips which form the backup memory any fault on that region could cause the SRAMs to be enabled on the bus while they should not, causing bus contention and preventing the CPU from reading the BIOS/BOOT program properly.

I'd say your top priority is clean the corroded area, investigate all traces which show signs of corrosion then put fresh parts on the positions which were affected by the said corrosion. Special attention for the 74HC32. It HAS to be a 74HC32 due to battery current drain concerns.

 

Fountain of information, i will pay particular attention to the 74HC32 area, i appreciate the pointers. here's pictures of the two places labeled "JP1" one on the top board and one on the bottom board Bottom board:



top board:

 

Oh no, that kind of jack is for connecting stuff. I mean, that board has so many chips it has auxiliary power wires which run from the bottom board to the top board. That's where one of the said wires connect at.

On newer boards you will find "JP1" and "JP2" as pads to place solder in for bridging.

A real fountain of information here:

http://wiki.neogeodev.org/

 

haha now why couldnt i find that while googling! doh!

 

Although l_oliveira is a master of Neo Geo repairs.

 

It's very encouraging you see a pink screen with random blocks (the blocks are on the fix layer) instead of no sync or a black screen. It means the graphics hardware is at least working enough to read the rom with the fonts and display a steady picture.

 

this is good to hear, i'll be ordering up some components on friday, when they arrive i'll get cracking on it.

is it prehaps possible that the 68000 itself is damaged? and if so can this be replaced by any similar 68000 chip say from a megadrive / elsewhere ? just a thought so i have everything ready(saves on the waiting which i hate!)

 

the 68k is standard, you can get one from many places.

Neogeo uses DIP and PLCC packages, not sure which uses which as I am still a neogeo novice.

 

excellent i though so but wasn't 100%

starting to get into arcade hardware = not good for bank balance but hopefully i'll have a (DIY)cab setup for Jamma/MVS and mame but that'll be way down the line. or maybe grab an old arcade cab if i can find one locally.

 

What is it with the MVS and corrosion, anyway? I know that arcade hardware sometimes ends up being used in rather hostile environments, but I've seen several MVS boards that were so rotten that parts are literally falling off the board - did they use extremely aggressive flux and not clean the boards properly or something?

 

This particular case it was the backup memory which leaked.

 

That and mice

 

they used a big ass rechargeable battery that likes to leak all over the place and they get left sitting in arcades and storerooms etc, i think some have even ended up in dumps / left outside or in damp nasty warehouses which doesn't help.

i recently got a MVS cart that on the inside had some kind of nasty smokey carbony smelling white substance (dried in) all over the inside of it. i think it'd been in a fire or flood or something lol. but it was sold as "contacts cleaned, tested and working" im thinking bullshit on that statement lol

edit: yeah rats and mice and bugs.

 

I know all about that. I just thought I could spare the disgusting details.

 

Arcade boards were built as cheaply as possible as they never really had to run for more then a year. Some chips from the 70s and 80s tended to have their legs zinc flashed with the legs being basic steel, so they tended to corrode from the inside into the chip even if they chip looked good. Makes trying to fix a board a pain in the arse. Williams Defender boards tend to have all the 7474 logic chips replaced for this reason...

 

I found that mice had built a nest under the shielding on my 6 slot! :\

 

lil uppydate - lol @ mice under the shielding, that doesn't surprise me, plenty of room for mices there

Got the ICs on order, one has arrived already but some coming from the good ol US of A, so may take their time.

Also, now have another MVS on its way a 4 slot board, so this should also help, its faulty too but less so than the 6 slot. games boot and play but just has some graphic issues.