NEO-SDR-T vendor or replacement?

[ic3b4ll]

It does but not how you may think. Look at the schematics page here:
https://wiki.neogeodev.org/index.php?title=File:Mv1fs-page4.jpg
You'll notice there's no NEO-SDR but rather another custom, the NEO-D0. The former is a replacement for the latter, with a few other functions.
What's most important though is that the Z80 is connected to everything.
In cases like these, any failed component would cause a Z80 error on all other board types using the standard BIOS.
There's only one bus. A stuck data or address line would make the Z80 hang.
How can you tell which one is bad?
You can't. You either remove the parts one by one until you find the fault or cut the power to them.
I've found many repaired boards with VCC pins clipped. If you do too, now you know why.
What can we do to make the repair efficient?
You already did something clever. You isolated the fault by testing the YM2610.
That leaves everything else and in that case you go by experience.
My experience tells me the Z80 in these boards tends to fail a lot.
That's why I told you to replace it.
Keep going, you'll get there.
Also, thanks to everyone who chimed in with further advice.

 

[rcboosted]

It does but not how you may think. Look at the schematics page here:
https://wiki.neogeodev.org/index.php?title=File:Mv1fs-page4.jpg
You'll notice there's no NEO-SDR but rather another custom, the NEO-D0. The former is a replacement for the latter, with a few other functions.
What's most important though is that the Z80 is connected to everything.
In cases like these, any failed component would cause a Z80 error on all other board types using the standard BIOS.
There's only one bus. A stuck data or address line would make the Z80 hang.
How can you tell which one is bad?
You can't. You either remove the parts one by one until you find the fault or cut the power to them.
I've found many repaired boards with VCC pins clipped. If you do too, now you know why.
What can we do to make the repair efficient?
You already did something clever. You isolated the fault by testing the YM2610.
That leaves everything else and in that case you go by experience.
My experience tells me the Z80 in these boards tends to fail a lot.
That's why I told you to replace it.
Keep going, you'll get there.
Also, thanks to everyone who chimed in with further advice.

ic3b4ll, thanks for the break down. I did indeed go over that schematic, but it's a bit hard to read and it has NEO-D0, which as you said too was replaced by NEO-SDR with additional function. I've watched almost every repair video GadgetUK posted, and his struggle with NEO-BUF lol. I was trying to figure out of the NEO-SDR does some buffering, or if Z80 tells it to do something to YM2610. I could not read it clearly enough in the schematic to determine one way or another. The dev Wiki asked that I test some connections to NEO-SDR, and I did get some weird readings, hence the thread. ack is sending me his Z80 from junk board, so I will have more definitive answer once it gets here. He's also including the NEO-SDR, but I'll replace that last since it's so leggy.

Thanks to everyone who chimed in!

 

[rcboosted]

Got the Z80 from @ack today, thanks for getting it to me so quickly! The z80 did indeed fix the issue! The pad had some corrosion on pin 24 (wait), I scratched it til it's showing all copper then tinned it. Passed all test from diagnostic bios including z80 test of course. But I lost audio on the left channel. A quick probe test showed the op amp wasn't outputting anything on left side. Swapped that out with an TI op amp and with the stereo mod, I got full audio. Oh I lost the pad on the op amp due to the stiff wire I used for stereo mod initially. It leveraged the pad off.

Wow, this board had so many issues. I think the onboard 12V amp isn't working either, got nothing through Jamma edge, I'm now wondering if it's a MVS supergun on JAMMA board issue, it fried all the way up the chain to the z80? The DAC didn't seem to be affected though. It was my first MVS board, or arcade PCB of any kind, so who knows what I did to fry so many things. *edit* can't be the supergun, I did not have the HAS til after the audio died on this board.

One more question though, is the stereo mod supposed to have audio that is super low in volume? I did the simple 6.8Kohm and 4.7uF stereo mod, not the MKL circuit, and audio is barely audible. Would low volume be a DAC issue? I doubt it. Anyways, here are some pics of my repairs.

 

[ic3b4ll]

Very good soldering work! Can you tell me what flux are you using?
Regarding wires, find a cheap VGA cable and strip it. It has 15 thin, flexible wires inside! But only the cheap, flimsy ones, though... Good quality cables have much better construction.
You can tell if the amplifier is working in a simple way... Rub your fingers on its pins and those of the surrounding area, including the pot and the capacitors. If you get some noise coming out, the amp is fine.
I've never done the stereo mod, but I bet the output is low when taken directly from the opamp. I wouldn't worry too much about it and it's certainly not an issue with the DAC.

 

[rcboosted]

Thanks! I tried to make it clean. The flux helped a lot. I used Chipquik recommended by GadgetUK. https://www.amazon.com/gp/product/B00CM2A97S I'm going to try some aliexpress flux too as well, just to see the difference. I might have some VGA cables, I'll check it out. Forgot about the finger test, I'll try that today. I've built a MKL amp already, but the ebay seller sent me the wrong transistor. Managed to squeeze it all into a 2cmx4cm proto board using through hole components.