Yes! Yes I would like to buy a MV4-FT2 for $20 - that sounds like a perfectly sensible idea.

[hatmoose]

z80's fail a lot compared to other cpu's -is it even the right one?
i'v seen a number of games overclocking slow ones.
cps1 and bubblebobble being 2 examples

I did lots more testing on this and eventually came away with a good idea of what is wrong

I took a known-good Z80 off the known good MV2FS, then put the suspect Z80 into the MV2FS = worked perfectly so no problem with the Z80
then I put the known-good Z80 into the MV4F = didnt work at all, so the problem on the MV4F is not the Z80

Then I took the top board off the MV4F and ran the standard Universe bios sound test, worked perfectly
Then I put the top board back on and ran the standard Universe bios sound test, nothing

So the problem is in the comms between the bottom board and the top board.

The top board is a pigsty - will clean it up so I can see what's going on and start looking for bad traces

 

[stj]

so maybe a multiplexer between the lower board and the romslots.
hopefully not a custom 4 chips in one package job.

 

[Raph_friend]

Replace the NEO-C1.

 

[hatmoose]

Replace the NEO-C1.

I was afraid you were going to say that...

 

[hatmoose]

So a quick wash of the top board and I think I may have to do some trace repair before messing with the C1

on the bottom board it looks like someone has replaced one of the AS245 chips wth an HC245 and bodged a resistor array onto the back


On the top board there is lots of corrosion, especially around the connectors between the two boards


And some of the G0 and 224's arent looking too clever either - I'm amazed that the thing works at all...


And some random track rot too.


It would be extremly tempting just to swap the top boards over, but SNK thought of this and have kindly offset the connectors by 2.5mm between the MV4T and the MV4-FT2...

 

[stj]

as afaik can handle more current than hc and is probably faster

 

[Raph_friend]

God only knows how many hours and what kinds of conditions these PCB had to endure.

 

[channelmaniac]

Given the way that this is failing I'm suspecting a bad z80

If it's the board you overvoltaged, replace the 6116 SRAM first.

 

[maki]

you really want the AS version of that logic IC, "Advanced Schottky" can't be replaced by the slower ones successfully IME

also, there is a lot of rotten traces on those PCBs

the dark patches/discoloured traces, every one of them is a candidate for being disrupted, vias can be rotten too

these PCBs have a high tendency for rotten traces, often on the top side where things just fell onto it and had decades to do stuff

for simple cases I scratch off the solder mask and re-tin the copper beneath it, if there is any left
short jumpers are fine, the shorter the better, you don't wan't to route fast clock signals through shitty jumper wires that are a foot long
these rotten traces can even be beneath ICs, but fixing the obvious ones comes first IMO

good luck, the MVS is a beauty, I'm a bit envious

 

[hatmoose]

Did some work on this over here too
https://www.neo-geo.com/forums/inde...h-neogeo-diagnostic-bios.267802/#post-4399650

TL;DR the 68k was bad which was causing the watchdog, and that bizare HS245+resistor array substitution was causing the garbled graphics. This problem would have been impossible to fix without the diagnostics bios which decoupled the watchdog problem from the HS245 problem.

Despite the shocking abuse that the top board has clearly been subjected to the z80 test cart will pass all tests in every slot.

So I'll swap that backup ram and see what happens next

 

[Raph_friend]

Great work friend.

 

[ic3b4ll]

So a quick wash of the top board and I think I may have to do some trace repair before messing with the C1

on the bottom board it looks like someone has replaced one of the AS245 chips wth an HC245 and bodged a resistor array onto the back


On the top board there is lots of corrosion, especially around the connectors between the two boards


And some of the G0 and 224's arent looking too clever either - I'm amazed that the thing works at all...


And some random track rot too.


It would be extremly tempting just to swap the top boards over, but SNK thought of this and have kindly offset the connectors by 2.5mm between the MV4T and the MV4-FT2...

My MV4 boards are stored away right now, but the resistor array is a factory bodge. I've seen it before and also thought it was a hack, but then I saw many boards with it, hot glue and all.

Don't worry about the track rot. Copper oxides are not like rust (from iron or steel). They actually protect the copper underneath from further corrosion.
The same can be said for solder. It may look ugly and actually be fine -- but I'd check for cold solder joints in this case.

Z80 errors can be a pain to nail down because they may be caused by a variety of reasons. Remember to check its RAM, the YM2612, etc.

Good luck!

 

[hatmoose]

So what happened when I swapped that backup RAM was a big nothing - the exact same error. Nothing wrong with the ram.

However there WAS something wrong with the trace FROM the ram to the 68x - a flaw so tiny I couldnt even see it under the microscope.

There IS continuity between the IO lines on the lower BRAM pads and the 68k
Lower BRAM pin 11 (IO1) goes to 68k pin 5 (D0)
Lower BRAM pin 12 (IO2) goes to 68k pin 4 (D1)
Lower BRAM pin 13 (IO3) goes to 68k pin 3 (D2)
Lower BRAM pin 15 (IO4) goes to 68k pin 2 (D3)
Lower BRAM pin 16 (IO5) goes to 68k pin 1 (D4)
Lower BRAM pin 17 (IO6) goes to 68k pin 64 (D5)
Lower BRAM pin 18 (IO7) goes to 68k pin 63 (D6)
Lower BRAM pin 19 (IO`8 goes to 68k pin 62 (D7)

There is IS continuity between other IO lines on the upper BRAM pads and the 68k
Upper BRAM pin 11 (IO1) goes to 68k pin 61 (D8`)
Upper BRAM pin 12 (IO2) goes to 68k pin 60 (D9)
Upper BRAM pin 13 (IO3) goes to 68k pin 59 (D10)
Upper BRAM pin 15 (IO4) goes to 68k pin 58 (D11)
Upper BRAM pin 16 (IO5) goes to 68k pin 57 (D12)
Upper BRAM pin 17 (IO6) goes to 68k pin 56 (D13)
Upper BRAM pin 18 (IO7) goes to 68k pin 55 (D14)

But, but but
Upper BRAM pin 19 (IO8`) should go to pin 54(D15) but in fact it does not

And the reason it does not... There was a tiny, absolutely invisible break in this trace


Here it is with the solder mask scraped off, still impossible to see


And here it is fixed - now Upper BRAM pin 19 (IO8`) does go to 68k pin 54(D15)


But the course of true love never does run smooth. Now I have to fix these three other pads I damaged in the process Then I should be able to clear the backup RAM error

 

[hatmoose]

So close - so close.

Have repaired the pads where I could, jumpered the other one, and re-installed the ram.

Now works perfectly in Slot 2 and Slot 3

Slot 1 has crackly audio and slot 4 is straight up dead - almost certainly bad traces since only some of the slots are affected, will check for contunitiy.

I also learned an interesting fact about the unibios 4.0. There are some bugs with the unibios in milti slot boards. Common manifestations of the bugs are
1) refusing to boot to game if slots 2/3/4 are populated but slot 1 is not populated
2) refusing to boot to jailbars if all slots are empty
2) no sound in games on slot 2/3/4 if slot 1 is not populated

So I'll start work on the crackly audio first, clean the slot then beep the traces

 

[xodaraP]

So close - so close.

Have repaired the pads where I could, jumpered the other one, and re-installed the ram.

Now works perfectly in Slot 2 and Slot 3

Slot 1 has crackly audio and slot 4 is straight up dead - almost certainly bad traces since only some of the slots are affected, will check for contunitiy.

I also learned an interesting fact about the unibios 4.0. There are some bugs with the unibios in milti slot boards. Common manifestations of the bugs are
1) refusing to boot to game if slots 2/3/4 are populated but slot 1 is not populated
2) refusing to boot to jailbars if all slots are empty
2) no sound in games on slot 2/3/4 if slot 1 is not populated

So I'll start work on the crackly audio first, clean the slot then beep the traces

It’s not unique to UniBIOS - the multi slot boards are very temperamental because of the way they address the ROM space

If you’re playing larger cartridges you often need to shuffle them around and have the larger carts in a lower slot

 

[ic3b4ll]

Slot 1 has crackly audio and slot 4 is straight up dead - almost certainly bad traces since only some of the slots are affected, will check for contunitiy.

It may be cut traces or the custom buffers may be shot. A single bad pin is enough to cause the issues you describe, though it usually affects slots in pairs. Check the pinouts on the Neo Geo Dev wiki and probe the outputs. Be careful not to short anything!
Also check for cold solder joints, it's somewhat common on the SMD chips.

 

[Raph_friend]

The AS245 and other AS ics can be replaced by HC models?

 

[stj]

no,
maybe AHC or AHCT but you need to check the datasheet
AS = very fast schotky, they can drive more current than HC and HC isnt as fast.

 

[hatmoose]

Slot 1 is now fixed -I'll post my notes and pinouts later but the TL;DR was

Symptom - distorted digtial audio on Slot 1 only. Digital Audio on all other slots OK, music on all slots OK. Passed neogeo diagnostics with z80 test OK.
Solution - No continuity between Slot 1 PROG B51 and NEO-G0 at C1 on pin 8. Jumpered Slot 1 PROG B51 to NEO-G0 at C1 on pin 8 to restore clear audio to slot 1

Details
Digital Audio is on the PROG board on the B (Bottom) side, SDPAD0 - SDPAD7 (B41-B4 and SPRAD0 - SPRAD7 (B49-B56)

Unfortunatley there is no easy-to-follow pinout for the MV4-FT2 top board so I had to beep and guess every single pin

Eventually found
SPRAD1(B50) went to pin 7 of the NEO-G0 chip at position C1 on the top board
SPRAD3(B52) went to pin 9 of the NEO-G0 chip at position C1 on the top board
BUT
SPRAD2(B51) went nowhere when it should (I assumed) go to pin 8

Reflowed NEO-G0 at position C1, no improvement
The broken trace was actually UNDER the NEO-GO at C1

Jumpered Slot 1 PROG B51 to NEO-G0 at C1 on pin 8 to restore clear audio to slot 1
here it is after I tidied it up a little bit - I left this one as obvious as possible so I can find it easily later.


So this one was not too hard, I already knew roughly where to look

The other fault on slot 4 (will not recognise cart) is going to be harder. There is no pinout for the MV4-FT2 and there are 240 pins on slot 4 that I need to check for continuity :-/ The good news is that slot 3 works perfectly, so the fault is more likley to be between the cart and those customs, than between the customs and the bottom board. So if I beep out every single pin on Slot 4 I can compare to slot 3 for clues...

 

[ic3b4ll]

Slot 1 is now fixed -I'll post my notes and pinouts later but the TL;DR was

Symptom - distorted digtial audio on Slot 1 only. Digital Audio on all other slots OK, music on all slots OK. Passed neogeo diagnostics with z80 test OK.
Solution - No continuity between Slot 1 PROG B51 and NEO-G0 at C1 on pin 8. Jumpered Slot 1 PROG B51 to NEO-G0 at C1 on pin 8 to restore clear audio to slot 1

Details
Digital Audio is on the PROG board on the B (Bottom) side, SDPAD0 - SDPAD7 (B41-B4 and SPRAD0 - SPRAD7 (B49-B56)

Unfortunatley there is no easy-to-follow pinout for the MV4-FT2 top board so I had to beep and guess every single pin

Eventually found
SPRAD1(B50) went to pin 7 of the NEO-G0 chip at position C1 on the top board
SPRAD3(B52) went to pin 9 of the NEO-G0 chip at position C1 on the top board
BUT
SPRAD2(B51) went nowhere when it should (I assumed) go to pin 8

Reflowed NEO-G0 at position C1, no improvement
The broken trace was actually UNDER the NEO-GO at C1

Jumpered Slot 1 PROG B51 to NEO-G0 at C1 on pin 8 to restore clear audio to slot 1
here it is after I tidied it up a little bit - I left this one as obvious as possible so I can find it easily later.


So this one was not too hard, I already knew roughly where to look

The other fault on slot 4 (will not recognise cart) is going to be harder. There is no pinout for the MV4-FT2 and there are 240 pins on slot 4 that I need to check for continuity :-/ The good news is that slot 3 works perfectly, so the fault is more likley to be between the cart and those customs, than between the customs and the bottom board. So if I beep out every single pin on Slot 4 I can compare to slot 3 for clues...

Check the Neo Geo development wiki. There's pinouts there and a rough board map.
No booting usually means a (CPU) data or address line is bad. If the associated custom buffer is shot address lines tend to get stuck high. You can check this quickly with a logic probe, no cart needed.

I commend your patience. Good luck!