Atari 7800 Pal RF quality issues

[Krool885]

Recently acquired a UK 7800.

The RF video is so bad it gives me headaches. It's not even just a bit of noise on the solid colours it's moving patterns of really prominent noise over different sections of the screen. 

 

Any help?

 

Thanks in advance.

[juansolo]

I'd like to say that's the worst I've seen but it isn't.

 

Short answer, if you want it to look good you need to AV mod it. But you need to manage your expectations when it comes to a PAL 7800. You ain't getting a super sharp picture without flaws out of one. You can get a passable composite video signal or a slightly better S-Video. There are a couple of tricks to getting it better still, but it ain't as simple as just dropping a UAV in there, the PAL machine is a little challenged...

 

There's a long thread where we went down this particular rabbit hole here:

My stock answer to this is that if you're not already deep into the PAL 7800 for some reason, get an NTSC machine, it's just a lot less pain all round. An option potentially in the future might be the 7800GD when that comes along as that's going to have it's own RGB out. But for now it all depends on how good a picture you want from it. A simple composite mod will look better. If you want the best possible picture out of it currently and you have a TV/monitor that can chew on S-Video, send it our way and we'll see what we can do. They're quite variable in terms of how good a result you can get form them, they can go from passable to really surprisingly good depending on the silicon lottery.

[Krool885]

I don't want a perfect picture. I put up with the fairly bad RF quality from a ton of my systems. A picture like the ballblazer in that thread would be good enough for me I think.

 

Edit: just realised that picture is probably already modded since it's your and you seem pretty expert.

 

Is an AV mod the only way? I don't feel qualified enough at soldering for that, and my current flat screen hates AV for some reason. I have to use RF on my n64 for that reason.

Edited December 9, 2022 by Krool885

[juansolo]

For us in PAL land, yeah. There's 3 electrolytic caps on a 7800 and they're nothing to do with the pic. There's some in the modulator, but if you're going to the trouble of pulling that thing off to recap it, you may as well just composite mod it because the picture will be massively better and it's actually easier. Plus, there's no guarentees re-capping it will fix it (it likely won't).

 

The PAL 7800 can just be that bad. As I say, some of them are even worse than yours. Though to be fair, your's is on the pretty  bad end of the scale. But it absolutely will be exacerbated by a modern panel being fed with old school PAL RF. It's hard to get one looking good even on a forgiving panel.

 

Try a composite console on your panel. See if it looks ok. That's honestly your best option.

[+karri]

Did you make a pcb of your PAL modifications? And is it available?

If not, I will try to make a PCB with SMD components.

 

I am stuck with a PAL unit and plan to write a game that runs on NTSC and PAL.

[juansolo]

There was no real demand for it to go to the hassle. For the handful we've done it was just as easy to build it on veroboard.

[+karri]

Thanks!

 

In that case I try to first buy all components needed. Then kick up KiCad to design the board. And buy a small set of proto pcb's.

 

The xtal seems to be available from China only. The rest of the components should be easier.
Hmm. I also found a 5V PAL xtal oscillator from Australia. Lol.

[juansolo]

We were getting them from France on eBay. But we haven't had any in ages.

 

Pretty sure this is up to date. Haven't looked at it in a while.

 

AntiJackModDocV3-5.pdf

Edited January 23, 2023 by juansolo

[+karri]

Thanks! I whipped out a KiCad schematics. The only thing I wonder about is the jumper between the luma and chroma. Is it ok? And the polarities of how the relay works.

PAL7800.pdf

 

Edit: I found your explanation in the docs.

[juansolo]

Yeah you don't need that jumper, but if you do put those two outputs together, you essentially get composite video.

 

I noticed I mentioned something about the Luma trimmer, that's not there any more so you can ignore that...

Edited January 24, 2023 by juansolo

[+karri]

I did order the components already. But today I started to think about missing the RF output. On a big screen the video is tolerable.

So I am wondering if the fix is worth the effort. Plus the RF works on my big screen. I don't know if it has S-Video.

Opinions? The Wizzy video is just work in progress.

[juansolo]

Honestly that's one of the best RF outputs I've seen from a PAL 7800, especially on a panel. If it ain't broke, I wouldn't fix it.

Edited January 28, 2023 by juansolo