Removing RGB jail bars idea?

[Anonymouse]

Hi there,
Im tired of every Mega Drive and Genesis I own having jail bars when using RGB or S-Video (it is alot more noticable on LCD screens). After looking at the video chip pin-outs and pin-ins I have an idea for a possible fix.

I recall someone saying the jail bars were a result of the lines on the video chip being to close. Therefor If you took the RGB signal before it enters the video chip then this problem could be removed?

Can someone with more technical know-how please comment. It would be awesome to make a Pro-RGB output for the Mega Drive.

[Genesis Knight]

RGB jailbars grind my gears. I'd be down for a fix, too.

[TmEE]

Jailbars in RGB are mostly caused by bad RGB cable which makes the TV go into an intermediate mode, showing both composhit and RGB at the same time. I've fixed many of such cables, usual problem is bad resistor value on RGB enable. Sometimes one needs to use Csync instead of Cvideo for sync.

[KillerBean2]

I recall someone saying the jail bars were a result of the lines on the video chip being to close.

That's part of the problem, true. But the main reason for the jail bars is interference by the PAL/NTSC sub-carrier signal (or so I've been told). If you stop this signal from entering the RGB chip on pin 6 (lift the leg or cut the line), the jail bars should disappear almost entirely. But it'll kill the PAL/NTSC encoding and leave you with RGB as the only video source.

Therefor If you took the RGB signal before it enters the video chip then this problem could be removed?

That's also an option. You'll need to amplify the RGB lines with a THS7314 or some similar chip.

[Genesis Knight]

That's part of the problem, true. But the main reason for the jail bars is interference by the PAL/NTSC sub-carrier signal (or so I've been told). If you stop this signal from entering the RGB chip on pin 6 (lift the leg or cut the line), the jail bars should disappear almost entirely. But it'll kill the PAL/NTSC encoding and leave you with RGB as the only video source.

So cut/bend pin 6 on the end that goes into the Genesis?



I wonder if my RGB->Component converter can handle the signal without the encoding. Any idea why the Saturn is different? I run it off RGB and there's no jailbars.

[Drakon]

I've never owned an actual rgb tv I've been encoding the signal to s-video. I tried mucking with the values of resistors and caps on the colour subcarrier circuit but nothing fixed it. I really don't think the jailbar problem is from the colour subcarrier line because the jailbars are an issue that shows up in luma when dealing with s-video. The colour subcarrier line should only effect chroma but not luma unless I'm mistaken. I was messing with the colour subcarrier line because it does effect the rainbow banding. I've even tried running a cxa2075 encoder off of a crystal oscillator instead of the system internal subcarrier. Using a crystal oscillator had a strange effect the jailbars started scrolling horizontally but they didn't seem to actually disappear. The only thing that was fixed by using a crystal oscillator was the rainbow banding went away. But unfortunately using an oscillator caused certain graphics to be a bit off sync and the picture wasn't as sharp looking.

Whatever the cause of these jailbars and the rainbow banding I don't think it has anything to do with how close lines are. This doesn't seem to be a case of the connections picking up interference. I read a lot of long threads where people were trying to fix it and it seems that these jailbars are actually an inherent flaw that comes with the chips sega was using. That means that the jailbars and even the rainbow banding come right out of the vdp chip and the ONLY way to fix these issues is to build some sort of hardware filter. Something else that points to the jailbars and rainbow banding coming right from the chip is the fact that these issues are present in every model of the genesis ever made. I've worked with the genesis 1, 2, 3, even the nomad. All these different genesis systems have very different pcb layouts and they all have the same stupid jailbars and rainbow banding.

The good news is I recently picked up a 32x, built a s-video mod for it that was far superior to the old 32x s-video mod, and discovered that the 32x 100% filters out the jailbars.



The 32x has now become a great piece of hardware you can use to filter out jailbars, it even makes the colours from the cxa1145 more vibrant. And the 32x outputs rgb by default and amazing s-video with a little modding. I even externally encoded the rgb coming out of the 32x into s-video and I don't remember seeing any jailbars on that either so that means the rgb coming out of the 32x should be just as jailbar free as the s-video it generates.

[KillerBean2]

So cut/bend pin 6 on the end that goes into the Genesis?

No no, I'm talking about the encoder chip, not the AV socket.

[Drakon]

Found some screenshots. Unfiltered s-video from the s-video coming out of the cxa1145 video encoder built into my model 1:



unfiltered s-video from the s-video of the 32x with my new s-video mod circuit



The difference? The jailbars simply went *poof* and completely disappeared which is so great. It's something I've wanted to solve for a long time and didn't expect to solve with the purchase of a 32x.

[Genesis Knight]

The 32X fixes jailbars on S-Video but not RGB. I was also excited at how the 32X cleans up the s-video signal back when I first got it, but I am running RGB from a 32X now and I have the jailbars. So it definitely doesn't fix RGB, just S-Video.

[TmEE]

I say bad RGB cable in such a case.

[lumclaw]

Next step is looking into Master System. I happen to experience rgb jailbars on a us model 1 sms. With the genesis vdp originating from there, it's likely not coincidence.

[Drakon]

The 32X fixes jailbars on S-Video but not RGB. I was also excited at how the 32X cleans up the s-video signal back when I first got it, but I am running RGB from a 32X now and I have the jailbars. So it definitely doesn't fix RGB, just S-Video.

Oh man that sucks so hard. That's so odd when I was encoding the rgb from the 32x into s-video I really don't remember any jailbars. So now s-video users have a solution but people who use rgb are still looking for an answer. Anyway you'd probably have to build some sort of hardware filter. When I had s-video with jailbars I installed a s-video splitter and had a 12 foot s-video cable branching off and attaching to nothing, this weakened the jailbars quite noticably. The same trick may work with rgb. It's a really ghetto trick and it's annoying having 12 to 20 feet of cable connecting to nothing but it's better than having jailbars. I first discovered this ghetto trick by accident when working with the rgb nes trying to solve the jailbars from that system. I had a scart switch and I forgot to press the button to disconnect the one long scart cord that connected to nothing. Having this extra long disconnected scart cord attached to the same circuit blurred the picture more and more depending on its length. But if you got the length of the cable right you could blur it just enough to filter out any video issues.

This's why I was so excited when I found the 32x s-video fix because now I no longer need 12 feet of s-video cable branching off into nothing. It's nicer having problem free video come right out the back of the console.

[TrekkiesUnite118]

Last I checked the 32X doesn't actually filter anything. It just uses it's own internal video encoder chip which may or may not be better than the one in your Genesis. RGB from the Genesis comes in, the 32X RGB get's slapped on top, and then that signal is sent to the encoder chip and output. So it's not actually filtering stuff out, it's just using it's own encoder which might be better than what your Genesis has. This improves Composite video, may improve S-Video, and does nothing to RGB. If you have a late model 2 Genesis that has the same encoder as the 32X, you won't see any improvement.

[Drakon]

Last I checked the 32X doesn't actually filter anything. It just uses it's own internal video encoder chip which may or may not be better than the one in your Genesis. RGB from the Genesis comes in, the 32X RGB get's slapped on top, and then that signal is sent to the encoder chip and output. So it's not actually filtering stuff out, it's just using it's own encoder which might be better than what your Genesis has. This improves Composite video, may improve S-Video, and does nothing to RGB. If you have a late model 2 Genesis that has the same encoder as the 32X, you won't see any improvement.

Uhm the rgb that's going into your 32x has already passed through the genesis encoder. You're not bypassing the genesis encoder when you use a 32x. I tried bypassing the genesis encoder and the picture was basically black because the 32x is expecting the rgb to be amped by the cxa1145. Also the encoder in the 32x isn't found in any model genesis it has way more pins. It's a custom made encoder that was only used in the 32x. I never said the 32x encoder is what does the filtering but something in the 32x is filtering bars away as my screenshots above demonstrate. And yes the s-video is improved, once again take a look at the screenshots.....once again for reference....

Unfiltered s-video from the s-video coming out of the cxa1145 video encoder built into my model 1:



unfiltered s-video from the s-video of the 32x with my new s-video mod circuit



Looks like an improvement to me..

[TrekkiesUnite118]

Uhm the rgb that's going into your 32x has already passed through the genesis encoder. You're not bypassing the genesis encoder when you use a 32x. I tried bypassing the genesis encoder and the picture was basically black because the 32x is expecting the rgb to be amped by the cxa1145

You are bypassing it for Composite and S-Video. And if your Genesis has a CXA1645 (Like many late Model 2s) you will see no improvement at all from using the 32X as that's the same encoder the 32X uses.