MV1A WRAM DATA error [ALMOST Solved]

[Retro Mecano]

Hi again,

Now that i am progressing (hope so) in my novice knowledge of MVS repair, i grabbed an old MV1A slot that considered as scrap.

First watchdog’ fixed that with broken trace on bios pins. But still only boots on diag bios. Stock and unibios still watchdog.

Second the diag screen is filled with scrambeled letters and lines, probed that back to the Neo-IO chip, swapped it and is finally fine.

Now i have WRAM DATA error as follows, and tried replacing first Upper ram, than lower, than back up, than bunch of H32 in the pin path, but no improvement.
It's exactly the same error occuring.

Tried to track wram traces, seemed fine, but not sure if they might be going to more than one direction.

This is the data i could gather, hoping someone can figure out what to check next.

 

[Retro Mecano]

Update

Half probleme solved.
I am really enjoying what i am learning through repairs and truly appreciate your advices.

Didn't pay attention to the diag screen in the bottom, which start/select seem to be active, even i unplugged the controller.

So this led me (a blind shot to be honest) to one of the 3 Neo-buf on the audio section, which on or some of them handle too the controller input. After swapping one by one, i found out that WRAM error disappeared wih the one on position GA7.

Now the WRAM error disappeared thankfully. I can boot Unibios m also, no more watchdog. The BUFs are pain the A** to diagnose.

Two problem remain:

-Start/Select still permanently active, Game goes directly to Unibios Cheat screen, and other buttons dont work. Not even directions.

-From the start of the repair, there's an annoying high scratch sound from speaker (like a vintage radio that gets no channel)

Any idea first on how to track down controllers ICs?
Later i'll deal with the sound.

 

[Retro Mecano]

UPDATE

Checking out continuity, found that PINs 10 & 11 of NEOBuf in GA8 where shorted.

Tracked it back to Resistor pack in CR6.

Comparing to other pack, pin 3 & 5 are not supposed to be connected. Seems it suffered a damage or current load.

Anyways, swapped it, and Start/Select are finally released. One problem solved!

Now final issue, games boot fine, still without sound, and diag with cart gives me following error, along with 2 beeps 1,0.

And here's the moment where usually @ack comes with his knowledge gauntlet to make this remaing half ofproblems disappear...

PS: stock bios give calendar error. Unibios works fine.

 

[Misos]

The Unibios skip calendar errors.
Side effect is that you can't save any game settings you change.
Try the backup ram tests in the diag bios.

 

[bodgit]

You can replace bad CRE401's with https://github.com/mourix/CRE401 if needed, it's slightly more than just a resistor array.

 

[ack]

Getting only 2 beeps is weird, perhaps there is some issue talking to the ym2610.

If its easy for you to update your diag m1, you can try this version

https://www.mvs-scans.com/misc/neogeo-diag-master-next.zip

It adds error addresses to the diag m1. After playing a beep code it will jump to a specific address in the rom and loop. Using a logic probe you can probe the address lines of the z80 to determine where it stopped and from that the error code.

There is more info here (search for "Error address for Z80")

https://github.com/jwestfall69/neogeo-diag-bios/blob/master-next/docs/error_codes.md

I'm not sure, but it maybe impractical to probe the z80 on a MV1A while a cart is installed.

 

[Retro Mecano]

Getting only 2 beeps is weird, perhaps there is some issue talking to the ym2610.

If its easy for you to update your diag m1, you can try this version

https://www.mvs-scans.com/misc/neogeo-diag-master-next.zip

It adds error addresses to the diag m1. After playing a beep code it will jump to a specific address in the rom and loop. Using a logic probe you can probe the address lines of the z80 to determine where it stopped and from that the error code.

There is more info here (search for "Error address for Z80")

https://github.com/jwestfall69/neogeo-diag-bios/blob/master-next/docs/error_codes.md

I'm not sure, but it maybe impractical to probe the z80 on a MV1A while a cart is installed.

Do i need to burn both new M1 and Sp1, or the new M1 works just fine with regular sp1?

 

[ack]

If you can do both I would do both, but just m1 is fine

 

[Retro Mecano]

If you can do both I would do both, but just m1 is fine

My GQ4x4 programmer decided today to fail every damn eprom writing for wathever reason... so was not able to make this M1.

Decided to use extermination approch and started socketing & replacing several IC.

Op AMP : innocent
Y3016 : Innocent
TA820: Innocent
Capacitors : innocent (lol for the moment)
2xHC273 : innocent
Neo-D0: innocent
6216 Ram: innocent
Z80 : half guilty

After replacing Z80, the anoying scratchy sound disappeared, and i got finally a new error and 001100 complete beep.

I think this gets to the starting point of @kissedin 's thread where he has exactly the same error on the same slot.

Damn what a coincidence..