*FIXED* MVS MV1 Jailbars on some sprites

[Brettster]

I got 3 dead MVS boards from Frothmeister
the best of the 3 started up with just a static green screen, I've since learned that this a calendar issue, usually caused by a leaking battery, Sure enough all 3 boards have had battery leaks.

Anyway I was able to get this to boot up using a universe bios, but It had no sound and a problem with the Graphics as seen below

Neo Geo boot up screen works fine, and most none animated graphics are ok

I was able to get sound working too by swapping the cartridge connector with one of the other faulty PCB's

coin up and controls work fine so this one is very close to being 100% working. just the lines to sort, am I right in thinking this is usually a RAM issue? if so how do I check which one it is?

I've been able to confirm connectivity with all the pins in the upper section near where he battery was and all the traces that look bad are still showing a good connection

Randomly probing with a logic probe did not bring this pcb back to life though

Brettster2018-03-10 16:16:14

 

[Flinnster]

Ah I will be awaiting answers and trying to learn on this one too. I have a non-booting MV1FS here and an MV1FZ with that same calendar error. I suspect similar .. that some chips have gone bad somewhere.

 

[robotech]

I have fixed a few of these recently with the calendar error (stuck on green boot screen )
Clean up all of the battery acid leakage
And repair any traces running to the
The calendar chip it is the one near the 32 mhz crystal
Also change the crystal and fit a coincell holder with rechargeable 2032

There is a test bios i have seen people using to test backup ram on socketed bios
Mvs boards robotech2018-03-06 03:35:51

 

[Layer]

Indeed, it seems to be a video RAM issue. Check them.

RAM locations : www.jammaplus.co.uk/forum/forum_posts.asp?TID=14082&title=neo-geo-tech-info-ram-locations

Layer2018-03-06 07:20:55

 

[pulstar]

Easiest thing to do is burn a diagnostics bios and see what the output of that is. You can download it here http://smkdan.eludevisibility.org/neo/diag/

 

[Brettster]

Cheers guys
the Diag bios sounds like a great place to start
sure i have a 27C1024 at home

 

[t-m]

This is the MVS clock circuit. You can check the crystal with a 'scope if you've got one also the outputs of the clock chip. I also had a dead 74HC32 produce the calendar error.

 

[Brettster]

everything in that area has had a dose of battery fluid by the looks of it
the Universe Bios ignores the issue and lets it boot anyway but will the Clock circuit work without a battery or is it needed to function?

I've removed the Batteries from all 3 boards that I have at the moment

 

[t-m]

The battery isn't needed for it to function, it'll just be forgetful when you turn it off.

 

[Brettster]

Happy to say this is now FIXED
after burning the Neo Diagnostics Bios everything came back as working!
so next I checked all the pins had connectivity from the main board to the cartridge slot, theres about 300000000 of them!!

they all checked out too
then I got the microscope out and carefully checked the whole board for broken traces and found one!

patched it with a jumper wire and BINGO!!

Another Neo Geo Saved

just 2 more to go now but they are not even booting up

one boots to a black screen

the other doesnt even get that far!
Brettster2018-03-10 16:19:46

 

[pulstar]

Cool. Nice fix there. With the non-booters first step would be to check the CPU is acting correctly, check the reset pin. address and data buses etc.

 

[t-m]

Nice fixing! I've got a 4-slot with track rot and it's driving me mad.

If you find the CPU resetting check the state of the bios chip socket... I had a couple recently pretty ropey, one needed replacement.

 

[frothmeister]

Great work dude. Glad to see you've got one up and running already

 

[bonehead]

Brilliant work and good info for future repairers.