Help with a Neo Geo repair

blonu

n00b
Joined
Sep 29, 2020
Posts
4
Hi,

I'm new here and new to Neo Geo. I recently acquired my first Neo Geo MVS 1 Slot board and when i looked at the board, i saw that the battery had leaked and eaten up 3 components completely. The first one, i believe is an osciallator, the second one looks like a tantalum cap and the third component only has legs remaining.

Here is the link to the images showing the board in the original form with the battery damage: https://imgur.com/a/fYVwsTN

After trying to guess what the components are on google, I ordered parts (20pf, 22pf and crystal) from digikey, hoping that the board will atleast show the cross hatch pattern.

I took the battery out along with the register that charges it, to replace with a CR 2032 battery holder and socketed the 8X2 chips as there seems to be considerable battery leak damage to the legs.

I traced a bunch of traces that looked like were worn out, but i do get connectivity on all but two of them, which i fixed.

Here is the link to the images showing a bunch of components removed around the battery to investigate the damage https://imgur.com/a/cGcZa1O

I resoldered everything back and got the crystal and couple of caps back. However, when it boots, it watchdogs between blue and white screen. Occasionally, giving a corrupt cross hatch. I put the unibios 4 and this is what it shows up as https://imgur.com/a/47lCh0Y

Any suggestions on how to proceed? Anyone here who can burn a Neo Geo diagnostic rom? Not sure if using that i will be able to read the screen or it will still be corrupt graphics.

Thanks
 

DaisyAge

Galford's Armourer
Joined
Jun 10, 2018
Posts
457
Hi,

I'm new here and new to Neo Geo. I recently acquired my first Neo Geo MVS 1 Slot board and when i looked at the board, i saw that the battery had leaked and eaten up 3 components completely. The first one, i believe is an osciallator, the second one looks like a tantalum cap and the third component only has legs remaining.

Here is the link to the images showing the board in the original form with the battery damage: https://imgur.com/a/fYVwsTN

After trying to guess what the components are on google, I ordered parts (20pf, 22pf and crystal) from digikey, hoping that the board will atleast show the cross hatch pattern.

I took the battery out along with the register that charges it, to replace with a CR 2032 battery holder and socketed the 8X2 chips as there seems to be considerable battery leak damage to the legs.

I traced a bunch of traces that looked like were worn out, but i do get connectivity on all but two of them, which i fixed.

Here is the link to the images showing a bunch of components removed around the battery to investigate the damage https://imgur.com/a/cGcZa1O

I resoldered everything back and got the crystal and couple of caps back. However, when it boots, it watchdogs between blue and white screen. Occasionally, giving a corrupt cross hatch. I put the unibios 4 and this is what it shows up as https://imgur.com/a/47lCh0Y

Any suggestions on how to proceed? Anyone here who can burn a Neo Geo diagnostic rom? Not sure if using that i will be able to read the screen or it will still be corrupt graphics.

Thanks

https://www.mvs-scans.com/images/f/f7/Mv1-1_set1_main_top.jpg
According to this it looks like a 20pf and 1k uf capacitor, not 22pf.
 

blonu

n00b
Joined
Sep 29, 2020
Posts
4
Thanks @DasiyAge, i'll try to order one as i don't have a 1 uf ceramic cap. I do have some smd ones, but not sure if i can give them a try.

Meanwhile, i was testing a bit more and reflowed solder on multiple chips and the cpu. It seems there is a problem with the video sync circuit. Here's the video where it appears the pvm respond with a clicking sound when the sync is reached and a cross hatch is displayed. Practically lasts for just 1 second. https://imgur.com/41jhqP1

Any clue on where on the board or which chip to focus on the attention next.
 
Last edited:

DaisyAge

Galford's Armourer
Joined
Jun 10, 2018
Posts
457
I'd start by checking the sync voltage at the JAMMA edge and reporting what you get, both with a game in and without. Also check the 24MHz crystal (near the cartridge slot) and make sure the solder joints are not cracked and the ground wire is secure.
 

blonu

n00b
Joined
Sep 29, 2020
Posts
4
ok, so i got the board to a state where there is just a calendar error. I believe the D4990 needs to be replaced. With Unibios i can get to the cross hatch and all the tests run fine now. I replaced all work and backup rams and 1 video ram. The palette rams were fine. No failures are reported in any of the tests with Unibios or the Diagnostic BIOS 0.19.

However, when i put a game in, i can do all CRC checks which report back fine, but i am unable to get past the mode setting screen. When i select exit, the board reboots with Unibios and back to the mode setting screen.
 

Misos

New Challenger
Joined
Aug 17, 2018
Posts
57
Something is activating the dip 1.
Go to the hardware test and press start until you get to the input test screen.
See if the dip 1 is on.
If the actual dip is off and it shows as it's on them you have a short somewhere.
The jamma harness, in the board itself, if the supergun has a test button maybe it's on, etc.
 
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