Neogeo test bios + z80 test cart - fails to solid blue screen on MV4F

[hatmoose]

Came back to this one after a long hiatus and a short temper tantrum.

Previous background here
https://www.arcade-projects.com/threads/bad-neo-io-on-mv4f-help-reading-the-pinout-please.25054/
I had indeed found the fault, but then destroyed the NEO-IO. Replacing it (more carefully!) with (another) known good one got me to watchdog, then fixing some light battery damage got me to "all tests passed" with the NeoGeo test bios.


I'm still using the old .19 release of the NeoGeo test bios, also check out the amazing new version from @ack here.
https://github.com/jwestfall69/neogeo-diag-bios/blob/master/CHANGELOG.md

I've actually got TWO MV4F top boards, one of them nearly works, one of them has a load of interesting problems that I'll deal with another day.

So the one that nearly works will play games in all slots with UniBIOS - but dead silent, no sound or crackling or anything.


The z80 test cart + Unibios gives behaviour that I have never seen before - fails to blue screen like this


Taking a video and watching in slow motion I get
Watchdog delay
Testing BIOS CRC32
Testing WRAM data
blue screen

So I'm a bit stuck - normally the z80 test cart gives at least some useful clues as to why the sound is dead - but in this case its like it can't even run the tests. Any thoughts gratefully appreciated!

 

[maki]

Oh mate, I was hoping for you to put this back up, I have a MV4F here as well with similar issues.. I swapped the ASIC around until I noticed a change etc.

What I've learned regarding sound on the MV4F/SLOT4F:
When I ran the test sounds from the BIOS (even without top board), they worked just fine: left, right and center
so I concluded that this part worked and the problem must be on the top board.Not sure if you did that already, but I'd try that first.

there is these MV4F specific ASICs and there is no modern drop in replacements for them (yet?).

there is one NEO-244 that handles Z80 address lanes at B2
then at E2 another NEO-244 for the ADPCM
for the https://wiki.neogeodev.org/index.php?title=NEO-244

There are just 5 74LS244 in one package, they act as buffer, each output goes to two slots: output 0 to slot 1&2, output 1 to slot 3&4, I'm assuming this was done to get better noise isolation between the slots.
With a scope its quite easy to test if everything works as it should, the two outputs should always mirror the input signal, others might prefer a logic probe for that.

Then there is another ASIC that handles sound stuff NEO-253 at 5E: https://wiki.neogeodev.org/index.php?title=NEO-253
I don't have a good idea on how to test these tbh, as I don't own a logic analyzer, maybe just plain probing would uncover obvious problems (stuck levels, no matter the inputs etc.)
Same as with the NEO-244, its a bunch of 74LS253 (dual 4to1 multiplexers) in one package, and as such they can be replaced by these discrete ICs (yeah that sounds weird if you spell IC out), but it takes 5 lCs and 60 wires to replace a single ASIC completely..

I'm not clear yet on what the NEO-G0 are there for, but for these you can get modern drop-in replacements.
Depending on if you're faster de- and re-soldering or probing, you can swap these ASICs with known good ones (like the ones in all the other positions IMO) instead of probing 60 pins per ASIC.

Edit:
I got my P Bus test PCB, but I am still waiting for parts (the S-RAM).
My idea was to swap the suspicious NEO-244 that are responsible for the sound (B2 and E2) with that one that is responsible for the P Bus at C2.
This way I could directly test them.

 

[ack]

It looks like your test cart is in backwards.

 

[hatmoose]

It looks like your test cart is in backwards.

The z80 test cart was in backwards.

Now that is is in round the right way I cn start testing. I actually have TWO top boards, both with different symptoms, have posted results from both here

Top board #1 is showing "z80 dead/errored/comm" in all slots
Expected = 03 in all slots
Actual = 01 in slots 1 and 3
Actual = FF in slots 2 and 4

I'm pretty sure this is not actually an error with top board #2. I think the fault is on the mainboard for the reasons below

Top board #2 is a comedy show. It is trying to say "z80 dead/errored/comm" but is having trouble doing so for other reasons - this is where the awesome advice from @maki will be bookmarked by me for ever. If others find this later in their own research and want to make their own Neo-G0/257/273/BUF/PCM check here https://github.com/neogeodev/NeoChips for some breathtaking work from @furrtek

But back to what Top Board #2wants to do, vs what top board #2 is actually able to do
Slot 1 will not draw text
Slot 2 will not draw text
Slot 3 garbled text - but its a good guess that it says "z80 dead/errored/comm" under the mess
Slot 4 garbled text - but its a good guess that it says "z80 dead/errored/comm" under the mess


So based on the fact that I'm getting the z80 error with both top boards, most likely the z80 error is on the bottom board. Changed the z80 for a known good one (unsurprisingly that did nothing). So I'm guessing a bad trace.

Unfortunately it's quite hard to probe the z80 when the top board is on I would have to build some kind off rig to stand the thing on its side while its running

So before I do that I can check the z80 pinout with the info here
https://wiki.neogeodev.org/index.php?title=Z80

And the connection between the bottom board and some of the top board here
https://wiki.neogeodev.org/index.php?title=MVS_board_connectors_pinouts

Any shortcuts or suggestions as always would be hugely appreciated!

 

[maki]

You got some really weird screenshots there

Reminds me of the ones I have from that MV4F with the broken NEO-244s, but they are quite different TBH:

Spoiler

These were caused by the NEO-244 being half dead at C2, that caused the P Bus not to work properly anymore.. things get funky then on these boards

What I find weird is that the slot pairs are 1 & 2, then 3 & 4, I'd expect errors to be present at least for each slot pair, but even in my case its not like that..

For simple starters:
just use the bottom board for basic tests, UniBios or an original BIOS will do, you want the basic sound tests (have to go into the test menu) without involving the top board at all.

https://wiki.neogeodev.org/index.php?title=Hardware_test

check this out:

View: https://www.youtube.com/watch?v=__qTYNFvl3I


this is how to probe the YM3016 to check if the digital part is okay, if you get that noise on Pin 4, it means the digital part is okay, if the analog is okay you will hear a sound (assuming your supergun is configured for stereo, mine wasn't at first, only silence then..)
https://wiki.neogeodev.org/index.php?title=YM3016

Pin 4 comes from the the YM2610 (OD0, Pin 31): https://wiki.neogeodev.org/index.php?title=YM2610