Problem with MV1B lower board

I'd appreciate any info on how to understand how to repair an MV1B board (specifically with the error below and any material in general).

Both upper and lower boards have a problem but I'm focusing on the lower one for now.
I have a good MV1B so I use the upper board from that and since I installed the Universe Bios it boots but after the first screen I get the following error: Exception Error Handling
Illegal Instruction
Address :00000000
AC ADRS:--------
R/W:-----
D0:000000FE D4:00000001
D1:000702AB D5:00FF00FF
D2:0012001B D6:00000001
D3:00000000 D7:00000002
SSP:FDFF2A30
SP:0000

My logic probe is ready if needed.

Also burned and installed the Neo Diagnostics BIOS
I get error
WRAM DATA (0000)
ADDRESS: 100010
ACTUAL: 2000
EXPECTED: 0000

So the chip indicated as RAM1 or one of the traces to it?

Since it was (0000) I guessed it must be the RAM1 chip. Checked all traces to 68K and no problems. Replaced chip and now I get BRAM UNWRITABLE (LOWER).
I've replaced the 74HC32A chip in the backup ram area but no luck.

auberwn said:

Since it was (0000) I guessed it must be the RAM1 chip. Checked all traces to 68K and no problems. Replaced chip and now I get BRAM UNWRITABLE (LOWER).
I've replaced the 74HC32A chip in the backup ram area but no luck.

Click to expand...

At least you get a different error now, that means (usually) that you are on the right track. Now it's complaining about the backup RAM...since these boards are not that expensive, are you sure this one is worth the time/effort to save it? or is it just a learning exercise you are doing?

aha2940 said:

At least you get a different error now, that means (usually) that you are on the right track. Now it's complaining about the backup RAM...since these boards are not that expensive, are you sure this one is worth the time/effort to save it? or is it just a learning exercise you are doing?

Click to expand...

Thank you very much for the reply.
Yes this a learning exercise mostly. I've been able so far to repair simple things (what the eye could see) but I would really like to be able to be able to diagnose further. Basically since I get addresses reported back I'd like to be able to tell how they map to actual hardware.
Of course there's also the fact that these boards are not that cheap where I'm from. I'd like to keep it as a spare.

Unfortunately when I go into the diagnostic bios menu and run the WRAM test I get the same error as before - which means I didn't actually fix anything? But then why did the error change at boot? Did I create more problems? The BRAM error is further down the list from the diagnostic bios page - are these run in the same order?

Anyhow I found that the BRAM error can be skiped when using the unibios and selecting switch to AES mode. But as the game boots up I get this error:
Address Error
Address: 0005DC28
AC ADRS: 8CD44295
R/W: READ
and the the other stuff

Can the BRAM error be skipped on the diagnostic bios as well?

Update:
I hadn't soldered of the legs HC32 from the backup RAM properly and when I removed the RAM1 it unconnected. Fixed that and I got the WRAM error again. I replaced the RAM2 and I got a ALL TESTS PASSED. So lower is like away from pin A and higher closer to it - logical. I soldered back the old RAMs on the RAM1 and RAM3 positions and again all tests passed.
So I plugged the Unibios in but no luck.
It boots but:
a) when I press A+B+C at boot the menu doesn't come up
b) with a game in, at the first screen where it says the region and mode the labels on the left of the description are missing (?!). Then a black screen and the an error at 00000000
c)I plugged the diagnostic bios back and I got MMIO DEAD OUTPUT. Can't find any info on that. I left it on for a while and I rebooted and it went away. If I leave it off for some time the error comes back and so on.

Hmm. I tried to burn the m1.bin from the diagnostic bios on my last EPROM but it failed. Grrrr. I haven't got an eraser yet. It's on it's way. Hopefully the sun will be out tomorrow.

As always if anyone has got any suggestion I would appreciate it very very much.

Apologies for bumping but I'm stuck and I'd appreciate the help.

At this point I either get on the diagnostics bios either "all tests passed" or MMIO error. I don't know what this error is.

On the 3.2 Unibios the buttons are unresponsive (A+B+C doesn't get me into the menu for example) and after the first screen I get an instruction error at 00000000.
The buttons work fine on the diagnostics bios.

I'd appreciate anyone's thoughts.

MMIO seems to be the chip responsible of mapping the memory to the IO. It sounds like the controller ports are managed by it. Since they do not work fine on your board, and sometimes an error is reported with it, it seems that particular chip has issues. Unfortunately MV1B boards are filled with custom parts that are not easily replaceable (SNK consolidated several chips into one custom) so unless the problem is just a bad connection, you may be out of luck.

Thanks for the info. That would be the NEO-SDR-T then. I'll check around it for any broken traces. Is there any info on the input voltage range of this chip?

Since the buttons work fine when using diagnostics bios could it be something further down from the NEO-SDR-T? RAM 6 seems to connect to it. And from what I read it stands between the 68K and the Z80.

auberwn said:

Thanks for the info. That would be the NEO-SDR-T then. I'll check around it for any broken traces. Is there any info on the input voltage range of this chip?

Since the buttons work fine when using diagnostics bios could it be something further down from the NEO-SDR-T? RAM 6 seems to connect to it. And from what I read it stands between the 68K and the Z80.

Click to expand...

The voltage should be the usual +5V , everything on neogeo boards (except audio amplifier) works with +5V. Regarding the erratic behavior of the controller...is it only on certain games? if so, maybe clearing the backup RAM will fix it.

Regards.

I have a blown MV1b with a bad main CPU/GPU and missing SRAM I pulled off it. could sell you on the cheap or buy yours to try and fix it.

-Segasonicfan

EDIT: ur in greece? hrmmm maybe not so cheap then cuz of shipping.