Problems with YUV video from VG-8020

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By Ace

Resident (53)

Ace's picture

09-06-2013, 06:08

So yesterday, I got a TMS9128NL to convert my VG-8020 to NTSC. The chip works fine minus bad colors with the on-board video encoder board, but that's not my main concern now. I want to get Component video off of this chip as well as Composite video working at the same time, though top priority is on Component video. Today, I got two small transistor buffer circuits wired to the B-Y and R-Y outputs since there's already a buffer on the Y output from the TMS9128 on the encoder board. The end result? Very sharp video with nice colors EXCEPT for one major problem:

THE ENTIRE SCREEN HAS A BLUE TINT!

What is wrong with this thing? No matter what I do, unless I weaken the B-Y output to the point where I can't see any more blue on my TV, there's always a blue tint over everything else. White text has a blue tint, blacks show up as a pure dark blue, and everything else has a layer of blue over it. Has anyone managed to get good YUV out of a TMS9x28? I'm seriously getting tired of consistently adjusting the circuit only to be running around in circles returning to the exact same problem. It's infuriating.

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By Manuel

Ascended (15686)

Manuel's picture

09-06-2013, 11:56

This doesn't help you at all, but why did you take the trouble to convert a European MSX to NTSC, instead of buying a Japanese MSX?

By Ace

Resident (53)

Ace's picture

09-06-2013, 15:33

Cost. That's all there is to it. It was cheaper for me to get a European MSX and convert it to NTSC rather than get a Japanese MSX, throw in a TMS9928 or TMS9128 depending on which of the TMS9918 or TMS9118 were used (I hate being limited to Composite video when better options exist) and wire up a Component circuit.

I haven't done any work since I posted about this yesterday, but I do have a few other details I left out:

-If I have Y and R-Y connected to the TV, the picture looks fine minus a lack of blue
-If all 3 signals are connected or just Y and B-Y are connected, the picture gets a severe blue tint
-If I put back the TMS9129, I get a GREEN TINT if I use Y and R-Y only, and I get the same blue tint if I connect all 3 signals or Y and B-Y only

And I don't seem to be the only person with this problem. I've seen several people attempt Component mods on a Colecovision (TMS9928) and they too have the same issue with the screen having a blue tint. Why that is, I have no idea.

Also, slightly off-topic as this is going back to Composite video: does anyone have a datasheet of the LVA510? I am incapable of finding any information on this thing and I'm having one hell of a hard time getting this encoder to encode video in NTSC. Something tells me since it's labelled as a "PAL encoder," it won't encode to NTSC. Or is there something I missed? Placing a 3.579545MHz crystal on the encoder results in the same blue tint I get with Component, but with the colors being completely wrong.

By Manuel

Ascended (15686)

Manuel's picture

09-06-2013, 16:11

Ace: most MSX2 systems have RGB out... if you can handle that, also very useful. And MSX2 is more interesting anyway, I'd say.

By Ace

Resident (53)

Ace's picture

09-06-2013, 18:21

I've got another VG-8020 along with an NMS8250 on the way. With this, I'll have 4 different MSX systems:

-NTSC-converted VG-8020
-MSX2-upgraded VG-8020 (I'll do this myself comparing the VG-8020 to the NMS8250)
-MSX2+-upgraded NMS8250 (have a V9958 on the way for this)
-1ChipMSX clone running on the Terasic DE0

I would have preferred to just have an MSX Turbo-R, but there's absolutely no way I will dish out the amount of money an MSX Turbo-R typically goes for, especially when I have yet to find anything I would actually run that absolutely requires the MSX Turbo-R and because those FS-A1ST/FS-A1GT computers have their volume levels messed up and too much low-pass filtering.

I specifically got this MSX after hearing about MSX games having altered colors on an MSX2 and up.

P.S. RGB is not an option in Canada. Our TVs don't accept RGB without having to resort to converters, hence why I want direct Component output from this VG-8020. With the others, I could just build an RGB cable to go to my RGB to Component converter. And if I can't get Component video out of the TMS9128, I'm gonna simply build the Sony HB-55P's video circuit to get RGB and Composite, then use my external converter to convert that RGB back to Component. This is messy, which is why I want to get direct Component video off this chip, but I absolutely cannot get rid of that stupid blue tint.

By ApolloBoy

Expert (96)

ApolloBoy's picture

09-06-2013, 22:50

Ace wrote:

P.S. RGB is not an option in Canada.

Er, don't they have Sony PVMs and Commodore monitors in Canada?

By Ace

Resident (53)

Ace's picture

10-06-2013, 00:20

I have a 1084S, but at 14", do you really think I would want to use that when I have access to a 27" CRT TV with Component inputs? Give me the big screen, not that small crap.

Now is someone gonna help me get Component video working correctly on the TMS9128 rather than going off-topic? I hate to sound rude, but I'm seriously losing my patience with this thing and am inching closer to just dumping a TMS9118 in this thing and say "screw Component."

By ApolloBoy

Expert (96)

ApolloBoy's picture

10-06-2013, 02:00

Why not pick up one of those ColecoVision component video kits that 5-11under has on AtariAge? It's not dependent on anything specific to the CV so it should work fine with the VG8020.

By Ace

Resident (53)

Ace's picture

10-06-2013, 02:04

I'd rather build my own circuit, not rely on a circuit someone else made.

By the way, do you have one of those Colecovision kits? How does that manage to get Component video without a blue tint?

By hit9918

Prophet (2866)

hit9918's picture

11-06-2013, 02:24

"THE ENTIRE SCREEN HAS A BLUE TINT!"

This reminds me of the emulators palette issue.
Something was odd about the TMS datasheet voltage levels...

wouter put a fix in openmsx 0.9.1 release, and in Renderer.cc of the sourcecode I find the comment:
"I assumed the "zero" for R-Y and B-Y was 0.47V"

Maybe both pins need a shift?

By Ace

Resident (53)

Ace's picture

11-06-2013, 05:49

A shift? What kind of shift, exactly? Do remember that I don't get any odd tints on the TMS9128 if I leave B-Y disconnected, however, on the TMS9129, I get a GREEN tint if I leave B-Y disconnected.

Just out of curiosity, what would an inductor do to the video output?

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