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dreamcast rgb

Started by phreak97, May 02, 2005, 02:27:17 am

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phreak97

ok, i wired up my dreamcast to test out rgb before buying a cable.
the h-sync was a tiny bit stuffed, on anything vertical you could see parts of the screen were vibrating left and right.. also the colour was a bit dark.

so, why?

TJ_Kat

I too, am less than impressed with the DC's upper output. I just fixed my VGA cable yesterday, and it looks interlaced. I thought all VGA was progressive. And if that's just a misconception of mine, how do I switch it so it is progressive?

Endymion

May 02, 2005, 10:58:50 am #2 Last Edit: May 02, 2005, 11:01:44 am by Endymion
VGA isn't interlaced. It isn't exactly "progressive," this is a term that only denotes HDTV, but it's generally synonymous with "non-interlaced," and that's exactly what the Dreamcast's VGA is. It's running at 640x480, which is not what a lot of people use their computers at these days, but 1024 lines or more is technically XGA, and, well the Dreamcast just wasn't made to use resolutions that high.

No clue why phreak's screen is vibrating, but I have no such issues, it looks great. I'd suggest  checking and rechecking the cable for any shorts, joints touching metal casings, etc. Being RGB (15KHz, and therefore interlaced), it's sure to be unrelated to TJ's issues.

NFG

Endymion, isn't it the case that 'progressive' is a consumer-level (ie: for dumbasses) term describing non-interlaced video?  "Ooh, it's progressive, it must be better!" says mom at the plasma TV store.  By this definition VGA is progressive, but no one calls it that 'cause VGA predates the progressive label.

It's true that DC VGA is amazingly great, if you've got trouble something's broken.

Endymion

Yeah it is a catchy marketing term now, but it is also true that a progressive broadcast locks the framerate, usually at 30, animation looks smoother just for not being interlaced though, and with more detail potential as with VGA. It's different enough that I wouldn't want to run around and say to everybody "My VGA monitor is progressive!" The difference in the type of broadcast is enough for me to want to segregate the terms.

TJ_Kat

*grumble grumble*

And here I thought I just got that thing fixed =(

I think I'll go dig out an old monitor to make sure my TV isn't just stupid.

Assuming it isn't my TV, I've got horizontal vibration in the image. Where should I start poking around?

NFG

For the price of a new VGA cable I dunno why you're trying to build your own.  High frequency video is a tricky thing to work out properly.  When I tried to build my own VGA box for the DC I failed also (though this was a looong time ago, back when I was a wee bit more clueless than I am now).

That said there's a few things to consider on your homemade project:

1. Make sure the schem you're working from is correct.  Maybe link to your source?

2. Check your wiring, then check it again (And again).  This is the most common problem.  Look for shorts and wires that just don't go the right way.

3. Check the quality of your soldering.  Cold solder joints or sloppy wiring will introduce noise into the circuit and when you're dealing with VGA any noise can cause trouble.

4. Make sure you're using quality parts.  While a cheap serial cable will work for a lot of projects you're gonna want a higher quality cable, like a VGA extension cable, for your VGA box.  Every little bit helps.

Martin

May 02, 2005, 10:27:38 pm #7 Last Edit: May 02, 2005, 10:37:13 pm by Martin
I went to a TV store the other day for a loo, I have to admit, I'm not impressed by the lack of progress PLASMA screens have made in terms of quality.
Lcd seems to have come on leaps and bounds though! :)
I know that was random, but I it just reminded me of seeing "PROGRESSIVE 100 Hz" proudly displayed on the cases of one of the TVs.
[span style=\'font-size:14pt;line-height:100%\']barenakedladies[/font][/span]

phreak97

i am getting horizontal vibration also, and im just using straight rgb

TJ_Kat

I DID buy a cable (because they're cheap). I'm not inclined to buy AN OTHER cable.

Anyway, that point is moot. After testing it on a proper computer monitor, I've come to the conclusion the cable works fine. The picture looks wonderful on the monitor.

Therefore, the problem is my TV. It does VGA, but apparently not all that well. Oh well, it still looks beter than composite.

So, phreak, I suggest trying it on a different TV first.


Endymion

Some cables are inherently crappy--if it works it really should Just Work™, but this is definitely another point for VGA boxes. They have a PCB that makes it a lot easier to identify a problem, and you can swap out cables as needed, not to mention getting different signals as you like or the need arises.

If you think it's your TV then I'd suggest tweaking the TV controls. You might find it has different options for how it handles progressive, scaled, VGA or other broadcast types.

viletim

phreak97,
There's nothing wrong with the RGB output of my Dreamcast. Did you remember to put ~220� capacitors in series with the RGB video signals?

phreak97

viletim, no, i didnt.. it doesnt say anywhere that i need to do that.. but why would overpowered colour cause crapped up h-sync? it might explain the poor colour.. but that was easy fixed by putting up the brightness/contrast anyway.. it's the sync i want fixed.

Guest

phreak97,
The coupling caps are mentioned on the gamesx DC pinouts page. Dunno about the sync issue.