Neo Geo MV1B woes

[hungar]

Hi all!

I've been wrestling with a MV1B over the last couple of days and I'm at a loss.

I was getting some weird graphical glitches and a backup memory issue. I ended up replacing some ram chips which sorted out the glitches but the backup memory issue still persisted, I ended up replacing both memory ram chips and also the 74HC32 in U1 used for the backup ram, I found a couple of bad traces from U1 pin 6 (which goes to pad 27 on ram 3) and 10 (pad 20) which i added jumper for.

This seemed to sort out the backup ram error, but no games would launch and checking the uni bios output I'm getting the general Z80 comms error if I disconnect the jumper from U1 to pin 27 I get the backup ram error again but I can just skip past this and games will work with no problem.

I've check over all the traces around ram 3 they all seem ok Ive switched out the ram chips and tried another 74HC32 but still the same, has anyone seen anything like this before?

 

[Ace`]

I haven't worked on this particular version but from looking at pictures it has two NEO-BUF chips, these have a massive failure rate and cause all sorts of odd issues.

Maybe swap them and see if you get any changes, if not that I'd say you're still looking for more bad traces. Neo boards are terrible for blown out vias and bad traces, not always because of batteries either.

 

[hungar]

Oh is that right, I'll give the Neo-buf swap a go thanks!
I have accumulated a pile of Neo boards over the years and this one was the last one left alive, I can't believe how unreliable they are

 

[bodgit]

My MV1B has also gone on the fritz; it was originally saying the upper backup RAM was bad, but I replaced that and got the exact same error so I think it's something else downstream. I've got some replacement 74HC32 chips somewhere to try replacing that but then I'm at a loss. Could do with a schematic if one exists, but I haven't found one yet.

Incidentally, the vertical slot PCB on mine has had the NEO-BUF replaced with one of those passthrough patches and I've never noticed a problem, but I do have some of the Furrtek replacements somewhere.

If you haven't tried it already, give the diagnostic BIOS a go too, assuming you have some sort of NeoBiosMasta installed if you have Uni-BIOS.

 

[hungar]

Good shout I just dug out the diagnostic rom, I don't have the cart to test the Z80, audio is working though so hopefully it's not that.
Well, it passed so no idea whats going on, I'll probably make the z80 test cart just to check but I'm definitely getting to the end of my tether.

 

[bodgit]

If you're looking to build https://github.com/jwestfall69/neogeo-diag-mvs-prog & https://github.com/jwestfall69/neogeo-diag-mvs-cha I have some blank PCBs left from when I made mine to save you getting five/ten made of your own. They were fabbed with the good quality settings ticked, (ENIG, hard fingers, chamfer, etc.) so they weren't cheap to get made but I'd just want to cover costs. You'd still need to source the components but would save you butchering an existing cart.