Dreamcast official VGA box

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thchardcore
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Re: Dreamcast official VGA box

Post by thchardcore »

Yes, it is visible in the bios and in game.

Here is my proposed fix as I have a spare Irken labs Trisync Helper which should attenuate the RGB lines to the proper level. Only issue is that it needs 5v source on VGA pin 9. See here:
https://irkenlabs.com/jammafier/tri-sync-helper

And here are photos of what I plan to do to address this:
https://photos.app.goo.gl/PUMdubMp9Yg2SaHD7

5V is supplied on DC multi AV pin 5 which is the white wire (pin 3) on the cable connection into the official Sega VGA box.

I will run a small wire from the 5V pin (white wire) to pin 9 on the VGA out connector. Then I will plug the TSH with the output set to H/V on sync.

Will double check my work before flipping it on, but I think to be safe, I should probably modify a VGA cable to remove pin 9 from the other side. Would hate to carry 5V to a location it isn't supposed to be, including possibly a ground.

Maybe someone can chime in to make sure my proposed power connection looks correct.

I previously added a 31/15 khz toggle by desoldering the composite phono jack and putting a screw in switch, so you can ignore that part of the wiring.
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thchardcore
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Re: Dreamcast official VGA box

Post by thchardcore »

Redid the attenuation of the RGB lines with 75 ohm resistors and happy to say the picture is excellent. I may try for 60 ohms as it is slightly less driven than my PS1 with the RT5 at default settings.
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Konsolkongen
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Re: Dreamcast official VGA box

Post by Konsolkongen »

I just tried this as well. I saw no improvements by attenuating the signal with 75 ohm resistors. In fact I got more noticeable ghosting than before, using my OSSC and having dialed in the phase as good as it allows.

Between the 10 ohm resistor and 0 ohm resistors I see no difference in amount of ghosing. So I just reverted back to stock 0 ohms and set the ADC gain on the OSSC to 7. This appears to solve the very hot output according to the 240p test suite. With 75ohm attenuation resistors I had to raise the ADC gain to 11 or 12 to get an acceptable image.

It's weird that you get a better image with 75ohm attenuation, but maybe that's an OSSC/RetroTINK 5 difference?
thchardcore
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Re: Dreamcast official VGA box

Post by thchardcore »

Not sure how the RT5 gamma adjustment compares with the OSSC pre-ADC function, but the issue I had with using only the pre-ADC adjustment on the OSSC is that the contrast always looked off. Physically modifying the box itself seemed to solve that but at the expensive of what appears to be an impedance mismatch, hence the visible noise.
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Gunstar
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Re: Dreamcast official VGA box

Post by Gunstar »

So with 480p/i RGB you need 10ohm resistors to attenuate. Does anybody know if S-Video needs any attenuation?
thchardcore
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Re: Dreamcast official VGA box

Post by thchardcore »

It shouldn't by all accounts.
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Gunstar
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Re: Dreamcast official VGA box

Post by Gunstar »

thchardcore wrote:It shouldn't by all accounts.
I only have one CRT with S-Video input setup currently but I'm seeing it blow out, similar to how my non-attenuated SCART is over RGB, variables could be the 3rd party cable not being made to spec or the CRT is at fault. I've also noticed that this 3rd party S-Video cable has strong red bleed on my NTSCJ Dreamcast but not on my PAL DC, does anybody know if there's an 'N64 situation' where Composite/S-Video require specific cables with regards to NTSC/PAL?
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Konsolkongen
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Re: Dreamcast official VGA box

Post by Konsolkongen »

Gunstar wrote:
thchardcore wrote:It shouldn't by all accounts.
I only have one CRT with S-Video input setup currently but I'm seeing it blow out, similar to how my non-attenuated SCART is over RGB, variables could be the 3rd party cable not being made to spec or the CRT is at fault. I've also noticed that this 3rd party S-Video cable has strong red bleed on my NTSCJ Dreamcast but not on my PAL DC, does anybody know if there's an 'N64 situation' where Composite/S-Video require specific cables with regards to NTSC/PAL?
S-video still relies on PAL/NTSC color encoding so that would explain the difference in quality :)
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Gunstar
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Re: Dreamcast official VGA box

Post by Gunstar »

Konsolkongen wrote:
Gunstar wrote:
thchardcore wrote:It shouldn't by all accounts.
I only have one CRT with S-Video input setup currently but I'm seeing it blow out, similar to how my non-attenuated SCART is over RGB, variables could be the 3rd party cable not being made to spec or the CRT is at fault. I've also noticed that this 3rd party S-Video cable has strong red bleed on my NTSCJ Dreamcast but not on my PAL DC, does anybody know if there's an 'N64 situation' where Composite/S-Video require specific cables with regards to NTSC/PAL?
S-video still relies on PAL/NTSC color encoding so that would explain the difference in quality :)
I get that the encoding is different but NTSC via S-Video on the N64 doesn't look like it does on NTSC DC via S-Video, as in it doesn't have a huge smear on red, which is why I bought up the N64 PAL/NTSC cable situation. I should probably grab some pics..
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Konsolkongen
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Re: Dreamcast official VGA box

Post by Konsolkongen »

Gunstar wrote: I get that the encoding is different but NTSC via S-Video on the N64 doesn't look like it does on NTSC DC via S-Video, as in it doesn't have a huge smear on red, which is why I bought up the N64 PAL/NTSC cable situation. I should probably grab some pics..
It could be that the encoding is just bad on the Dreamcast. Like how composite on the PC Engine is “pretty good” and it’s god awful on the Mega Drive and all other systems using the CXA1145 RGB encoder.
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