MV1A Display Problem

Xian Xi

Xian Xi

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Working on an MV1A for a friend and noticed a few weird things.

Upon boot at the Unibios splash the Neo Geo text has a red outline.

During the color test I get this:

mv1a-video-problem.jpg


Palette RAM?


On a side note, I never knew Neos had PALs:

mv1a-pals.jpg


Also can anyone confirm that R48 on the under side of the PCB for the Video DAC is valued at 220ohm? It looks like it was resoldered.
 
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Xian Xi

Xian Xi

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Did some probing, Color RAM 7 for pins 16-25 are all low.
 
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smkdan

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It's hard to tell from the really bright pic but is there a red tint on the middle white bars that gets progressively whiter towards the right? Is there only 1 or 2 shades of red on the top? I think it's the red portion of the DAC. You only see the brightest red bit and the rest aren't showing at all. It explains the half bars of red being black + half teal bars on white and the too much red on white neo logo. I don't know how the MV1AX DAC is laid out but I know that 220ohm is for the highest intensity bits for each color component. Maybe something is wrong with the soldering or the other resistors were cut leaving only the 220hm one working. That would explain what I see on screen.
 
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Xian Xi

Xian Xi

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Tested the resistors in the DAC and was shocked to find 4 dead ones and 3 that were completely off (22o? They read at 8k). Replaced them with good working resistors, check the values and now they are all good.

But the problem isn't completely fixed, it now looks like this:

mv1a-video-problem1.jpg
 
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smkdan

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That's much better but there's still 1 other red component left out. If you know the red 1K resistor is fine then check this:

upper palette ram (12) -> upper 273 (4)
upper 273(5) -> 1K red resistor -> JAMMA red
 
Xian Xi

Xian Xi

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smkdan said:
That's much better but there's still 1 other red component left out. If you know the red 1K resistor is fine then check this:

upper palette ram (12) -> upper 273 (4)
upper 273(5) -> 1K red resistor -> JAMMA red
Click to expand...

I'll check that later tonight. What are the resistors with the 22o(actually o with a dot under it) on them?
 
Xian Xi

Xian Xi

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smkdan said:
That's much better but there's still 1 other red component left out. If you know the red 1K resistor is fine then check this:

upper palette ram (12) -> upper 273 (4)
upper 273(5) -> 1K red resistor -> JAMMA red
Click to expand...

100% continuity.
 
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smkdan

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Something else might be making it appear as if that line is dead or the DAC is different compared to other boards. If you don't have anything else to try then try swapping the 273s around. I noticed the schematic PDF had the palette lines shuffled around and they don't match what I posted, but you wouldn't get continuity if yours was also like that and my spare 1FT is the same too. Is there anything about the DAC that doesn't match the old boards apart from the component size? I don't see any good pics of it around here.

R1: 6264L D0(11) -> 273L D0(3) Q0(2) -> 2.2K -> JAMMA R
R2: 62624L D1(12) -> 273L D1(4) Q1(5) -> 1K
R3: 6264L D2(13) -> 273L D2(7) Q2(6) -> 470
R4: 6264L D3(15) -> 273L D3(8) Q3(9) -> 220

B0: 6264L D4(16) -> 273L D4(13) Q4(12) -> 3.9K -> JAMMA B
G0: 6264L D5(17) -> 273L D5(14) Q5(15) -> 3.9K -> JAMMA G
R0: 6264L D6(18) -> 273L D6(17) Q6(16) -> 3.9K -> JAMMA R

DAK: 6264L D7(19) -> 273L D7(18) Q7(19) -> LS05 (9,11,13), then output to each 8.2K
Click to expand...

^ that's what I have on the upper palette RAM from my 1FT. The bolded one is what you checked and what would cause that pattern on mine.
 
Xian Xi

Xian Xi

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Tested all those and they are all connected 100%.

I think it might be something with the green actually since green kills red in color mixing.

Can you post what the green DAC is?

On the board the palette ram is I think 6265 and not 6264 and looks to be an off brand.
 
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furrtek

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Wait... A neo-mga and PALs on a mvs board ?
Would you be kind enough to take a picture of the complete board for the wiki ?

(sorry, can't really help for your dac problem)
 
Xian Xi

Xian Xi

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furrtek said:
Wait... A neo-mga and PALs on a mvs board ?
Would you be kind enough to take a picture of the complete board for the wiki ?

(sorry, can't really help for your dac problem)
Click to expand...

Yup, this board is all kinds of weird.

I'll try to scan it, I'll ask for my sister's scanner. Thanks for all the tech stuff on the Wiki, you guys are doing an excellent job.

PM me an addy to send it to when I'm done scanning it.
 
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furrtek

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Great, thanks a lot :) Glad you like the wiki too, I bet the other contributors are also proud of where it has gone today.

Nice to see a new curiosity. since the release of the official dev docs, there hasn't been much new stuff to dig around (except about the neoprint boards and the internals of the graphics chips).

Hope you'll get your colors problem sorted out.
 
Xian Xi

Xian Xi

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I replaced the palette RAM and the upper 273 and the problem still remains.
 
Xian Xi

Xian Xi

JammaNationX,
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Weirdly, I think the 1k died after I fixed the 220 because it was dead all of a sudden. Replaced the 1k now and it's fixed finally. Weird how I tested it before and it was reading fine at 987 and now dead.

Thanks smkdan again.
 
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