Dreamcast isn't outputting green signal (in RGB)

[Ziggy]

I was posting about this in another thread, but now that I'm completely stumped...

I wanted to make this so I could use the DC with the Framemeister: http://dcemulation.org/?title=Dreamcast ... ster_Cable

What's wrong with my sync combiner?

EDIT: As it turns out, nothing was wrong with the sync combiner RGB thing I built. I tried it on a second Dreamcast and it works perfectly. However, now I have to figure out what's wrong with the first Dreamcast.

This is the picture I get:



Note the Y button on the controller, it's not green at all. Actually, it's black. Leads me to believe that the green signal is missing entirely. We know red isn't missing, obviously, and blue is clearly there as well.

Jump to this post (to skip me finding out there was nothing wrong with the sync combiner): viewtopic.php?p=998818#p998818

UPDATE: I acquired a few Dreamcast mainboards from eBay, they both turned out to be dead. But I swapped out the video encoder chip and now the RGB output is working perfectly. So as it turns out, the green signal was missing because there was something wrong with the video encoder.

[pierrot]

Yikes, okay. I see what you're working with now. My issue was slightly different, and off of an idea you mentioned in the other thread, I tried some 240p/480i only games with my setup. Curiously, it seems like my issue was solved through some fiddling that I'm willing to attribute to turning off 12bit color, changing power cords, or just getting a better fit to the RGB cable <-> Hanzo connection.

That's pretty severe. You're right, the sync circuit shouldn't affect the colors. You're sure there's continuity on the color lines from output to input? Are any of the pins on the DC connector bent at all where they might not get a good contact, or touch the metal around it? Have you tested it without the capacitors on the color lines?

I had an issue like that with the VGA cable that Racket used to sell in his storefront, except I think I was getting blue, and not red. I didn't mess with it, though; just traded it for the VGA box. Seems like it should be something along the Blue and Green lines, or ground, in your situation, though.

[Ziggy]

You're sure there's continuity on the color lines from output to input?

I checked continuity for each color line as such: Continuity between the DC AV connector and the positive leg of the cap, and continuity between the negative leg of the cap and the corresponding pin on the SCART connector. I also checked the all three lines are wired to the correct pins (not swapped around) and that there are no shorts to ground on any of the lines.

Are any of the pins on the DC connector bent at all where they might not get a good contact, or touch the metal around it?

Yeah, actually. One of the RGB pins on the DC connector was a little recessed compared to the other pins. I used a needle to bend it so that it matches the length of the other pins. But that's a good point, maybe the G or B pin isn't making good contact with the AV port. The only way I can test that is if I open up the DC, plug the cable in, and check continuity between the SCART end of the cable and the solder point on the motherboard. It'll be a pain in the ass to do it, but I suppose I have to so I can rule it out or find out that it's the problem.

Someone on the Nesdev forums said that since I have a massively red screen, and the Y button on the controller doesn't look green (it's actually black - I didn't notice this) that I might possibly be missing the green signal.

Have you tested it without the capacitors on the color lines?

No, but every source on the net says the RGB lines need those caps. I did swap the caps around when I rewired it with the second cable, so that effectively rules out a bad cap (I never had brand new cap that was bad - but I suppose that's possible!).

___

When I get home I'll check continuity to make sure the DC connector is making a good connection with the AV port. Now that I think about it, it's also possible that the pins on the cable or the console are dirty. Both the console and the cable were stored in a (humid) basement for a few years without use. I'll clean both and check continuity from inside the console. Thanks for the suggestion.

[Ziggy]

OK, so I pretty much found out what the problem was.

The green channel is missing. I tested the RGB box thing on a different Dreamcast and the picture looks perfect. So there was never a problem with the cable, it was the Dreamcast! Go figure. I tried cleaning the AV pins on the console, but it still isn't working, I'm gonna have to open the console up to figure out what's wrong with it.

But yeah, the RGB box thing works great!

[Ziggy]

OK, so I did some more testing, and I just can't figure out what the problem is.

I cleaned the AV pins a bunch of times, so I'm sure it isn't a dirty connection. I also have continuity between the cable and the solder points on the motherboard, so I'm sure it isn't a bad connection between the cable and the console.

I checked continuity from the green pin on the AV output all the way back to the video encoder. So... there's continuity from the green output all the way to the end of the cable.

One thing I noticed is a little screw mark on the motherboard, it was made from one of the mounting screws for the GD-ROM drive. And would you know, it's RIGHT below the via that goes to the green pin on the AV output. So, even though there's continuity all the way back to the video encoder, I thought that screw mark might be a problem (it's the ONLY thing I can find). So I soldered a jumper wire between two points that jumps the screw mark but doesn't omit any components. I had high hopes for this one, but still, same red picture as always.

I checked composite output from this console, and it works fine, for whatever that's worth.

I'm really stumped. It's like the video encoder isn't outputting green.

Anyone have any ideas?

[Cronozilla]

Maybe there's an issue with the chip itself?

[Ziggy]

Maybe there's an issue with the chip itself?

At this point, that's the only thing I can think of.