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Thread: MD/Genesis Jailbars Revisited

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    Electron Guns Nameless One CathodeRayTubes's Avatar
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    Default MD/Genesis Jailbars Revisited

    It has been discussed with great detail and theories by a lot of people and on multiple forums but I want to see it through is there really no fix for the jailbars. Anyway on to some of the things I have tried and then on to other things I will try. First of all I have mainly seen that with the proper cable setup in RGB the jailbars come in faint, and if the sub carrier has been cut from the encoder then they are almost not visible at all. In the encoded video they tend to show up full on, some tvs filter it out a bit others dont so well. I have tried the external subcarrier clock before with no success the jailbars were there and were moving which I found that a clock divider is necessary to have a proper subcarrier, but even there it doesnt fix jailbars, I have tried 10k pots on the sync line, no fix. There is another thing I have in mind and its something Tiido came up with back in 2008 on the nfg forums how he had used raw H and V sync from the VDP direct to make a clean composite sync signal jailbar free but was not able to get an encoder to work with it, this is something id like to experiment around with a bit, though if this is the fix then the interference is coming from composite sync, and im not even sure that all the sega ASICs have pure H and V sync but atleast the early ones do, I think this is possibly the last idea we can try to resolve jailbars besides tapping the digital pixel data from the early vdp ASIC (315-5313). I also am gonna try to hook the H and V sync strait to my pvm-2030 since it allows for separate sync input to see what results it has. Hopefully this time around we find something
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    Master of Shinobi MaxWar's Avatar
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    Sorry if this sounds stupid but im not 100% sure of what type of jailbar you are talking about. I know of two types of jailbars on the Genesis.

    -The obvious, large Jailbars of the Model II genesis with Samsung Encoder.

    -The thin faint jailbars you get when when using S-video ( and possibly RGB idk ). I got them on both my s-video modded model 1 (va3) and on the Game gear console i am currently working on. The only thing i know about this is that it can be much minimized by using a resistor on the chroma line. If adjusted just right they get so faint that you usually dont see them at all.

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    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    It's also a subcarrier issue on S-Video, but purely a Sync issue on RGB.
    Maybe combining both the H-Sync and V-Sync from the 5313 VDP with a NOR gate will solve it?


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    I had the same problem as you trying to find out if for sure I could not get rid of the jailbars.
    I found I was able to completely remove the jailbars by removing C28. See here. I believe that its the one right above R23. I literally just scratched it off the PCB when trying to desolder it.
    There are no jailbars and it probably looks the best out of all my RGB consoles. I tried it on my PVM-2030 and my PVM-2950Q and got the same great results.
    I have a TMSS High Def Graphics Model 1.


    Quote Originally Posted by CathodeRayTubes View Post
    It has been discussed with great detail and theories by a lot of people and on multiple forums but I want to see it through is there really no fix for the jailbars. Anyway on to some of the things I have tried and then on to other things I will try. First of all I have mainly seen that with the proper cable setup in RGB the jailbars come in faint, and if the sub carrier has been cut from the encoder then they are almost not visible at all. In the encoded video they tend to show up full on, some tvs filter it out a bit others dont so well. I have tried the external subcarrier clock before with no success the jailbars were there and were moving which I found that a clock divider is necessary to have a proper subcarrier, but even there it doesnt fix jailbars, I have tried 10k pots on the sync line, no fix. There is another thing I have in mind and its something Tiido came up with back in 2008 on the nfg forums how he had used raw H and V sync from the VDP direct to make a clean composite sync signal jailbar free but was not able to get an encoder to work with it, this is something id like to experiment around with a bit, though if this is the fix then the interference is coming from composite sync, and im not even sure that all the sega ASICs have pure H and V sync but atleast the early ones do, I think this is possibly the last idea we can try to resolve jailbars besides tapping the digital pixel data from the early vdp ASIC (315-5313). I also am gonna try to hook the H and V sync strait to my pvm-2030 since it allows for separate sync input to see what results it has. Hopefully this time around we find something

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    urusei yatsura Master of Shinobi lumclaw's Avatar
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    One type of RGB jailbars previously appeared on Master System. I don't know if the Mark III had them.

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    They're visible on any unit using a CXA1145, which is why some master systems have them and others don't. They're present on the Neo Geo AES, too. The VDP isn't the culprit, and grounding out the subcarrier line on the SMS does nothing for my setup. There's gotta be something else at work...

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    I wonder if the copper wrap trick works? The same trick used for famicoms or nes's.
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    Problem is the PCB design and weak signals. Cut the RGB lines from the VDP and CXA side and run them with a shielded cable and you'll no longer have jailbars.



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    I thought the jailbars were caused in the CXA1145, by the composite clock interfering with the blue color, which is why disconnecting pin 6 of the CXA (the clock input), or C28 which is leading to pin 6, would get rid of the jailbars almost completely.

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    Quote Originally Posted by CathodeRayTubes View Post
    It has been discussed with great detail and theories by a lot of people and on multiple forums but I want to see it through is there really no fix for the jailbars. Anyway on to some of the things I have tried and then on to other things I will try. First of all I have mainly seen that with the proper cable setup in RGB the jailbars come in faint, and if the sub carrier has been cut from the encoder then they are almost not visible at all. In the encoded video they tend to show up full on, some tvs filter it out a bit others dont so well. I have tried the external subcarrier clock before with no success the jailbars were there and were moving which I found that a clock divider is necessary to have a proper subcarrier, but even there it doesnt fix jailbars, I have tried 10k pots on the sync line, no fix. There is another thing I have in mind and its something Tiido came up with back in 2008 on the nfg forums how he had used raw H and V sync from the VDP direct to make a clean composite sync signal jailbar free but was not able to get an encoder to work with it, this is something id like to experiment around with a bit, though if this is the fix then the interference is coming from composite sync, and im not even sure that all the sega ASICs have pure H and V sync but atleast the early ones do, I think this is possibly the last idea we can try to resolve jailbars besides tapping the digital pixel data from the early vdp ASIC (315-5313). I also am gonna try to hook the H and V sync strait to my pvm-2030 since it allows for separate sync input to see what results it has. Hopefully this time around we find something
    Thank you I'm so tired of people saying that using an external subcarrier source removes jailbars it just makes them scroll. The 32x generates its own subcarrier and somehow is in sync with the genesis. If you want an example of how to do it right, I believe omp posted sega service manuals here:

    http://www.sega-16.com/forum/showthr...anuals-on-eBay

    I believe there's a full 32x schematic contained in these. Probably a good idea to study the oscillation circuit of the 32x to figure out how it works as it pretty much kills all jailbars over s-video.

    Quote Originally Posted by LaC View Post
    I had the same problem as you trying to find out if for sure I could not get rid of the jailbars.
    I found I was able to completely remove the jailbars by removing C28. See here. I believe that its the one right above R23. I literally just scratched it off the PCB when trying to desolder it.
    There are no jailbars and it probably looks the best out of all my RGB consoles. I tried it on my PVM-2030 and my PVM-2950Q and got the same great results.
    I have a TMSS High Def Graphics Model 1.
    Removing c28 disconnects the subcarrier from the encoder which is the rgb jailbar fix. Doing this removes colour in s-video, composite, and rf video.

    I like the idea of having something that you can just plug into your genesis to fix the jailbars without having to mod the genesis itself. What tiido is suggesting makes a lot of sense. The rgb signals from the vdp are unamped and I've discovered messing with the rgb nes and other mods that unamped video signals tend to pick up noise very very easily. Once a video signal is amped then it doesn't pick up noise but before it's amped it's extremely susceptible. The signals don't get amped until they hit the video encoder however they travel across most of the pcb and under a lot of chips before they reach the video encoder. Probably the best solution is to tap the rgb as close to the vdp as possible and have them fed into a video encoder with the shortest distance possible. This method fixes jailbars on the rgb nes as well. I'll wire up a unit when I have time and test this out.
    Last edited by Drakon; 05-31-2013 at 09:33 AM.

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    Quote Originally Posted by villahed94 View Post
    Maybe combining both the H-Sync and V-Sync from the 5313 VDP with a NOR gate will solve it?
    The sync polarity is negative. I think you need an AND gate to combine them... But I could be wrong?
    Last edited by KillerBean2; 05-31-2013 at 09:44 AM.
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    Quote Originally Posted by Drakon View Post
    Removing c28 disconnects the subcarrier from the encoder which is the rgb jailbar fix. Doing this removes colour in s-video, composite, and rf video.
    So, nothing of value is lost!

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    Quote Originally Posted by zyrobs View Post
    So, nothing of value is lost!
    RF Video has value. What if you bring your Genesis to a cheap motel. Now what?
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    Quote Originally Posted by MaxWar View Post
    Sorry if this sounds stupid but im not 100% sure of what type of jailbar you are talking about. I know of two types of jailbars on the Genesis.

    -The obvious, large Jailbars of the Model II genesis with Samsung Encoder.

    -The thin faint jailbars you get when when using S-video ( and possibly RGB idk ). I got them on both my s-video modded model 1 (va3) and on the Game gear console i am currently working on. The only thing i know about this is that it can be much minimized by using a resistor on the chroma line. If adjusted just right they get so faint that you usually dont see them at all.
    Basically all the jailbars that you get in all setups of the Genesis board revisions, all of them have it to some degree even the genesis 3, however I have not been able to test a VA2 or a VA2.3 model 2 but have tried all the rest of the revisions and they all suffer from jailbars to some degree, these show up close together and as far as the samsung one im sure that if its fixable even the samesung can be fixed its just the samsungs show it much worse than the other encoders.

    It's also a subcarrier issue on S-Video, but purely a Sync issue on RGB.
    Maybe combining both the H-Sync and V-Sync from the 5313 VDP with a NOR gate will solve it?
    Im hoping to try this and feed it to an cxa2075, though I have just one other thing I have not tried, there is a 2.2k ohm resistor to +5v on composite sync on all board revisions all the way to the genesis3, without this resistor sync does not work, though I want to try a transistor on it a c945 to amp the sync and see if that works I think there is possibility of interference with the voltage, I am gonna check all these things.

    Thank you I'm so tired of people saying that using an external subcarrier source removes jailbars it just makes them scroll. The 32x generates its own subcarrier and somehow is in sync with the genesis. If you want an example of how to do it right, I believe omp posted sega service manuals here:

    http://www.sega-16.com/forum/showthr...anuals-on-eBay

    I believe there's a full 32x schematic contained in these. Probably a good idea to study the oscillation circuit of the 32x to figure out how it works as it pretty much kills all jailbars over s-video.
    I am gonna look into this soon as well, I will let you know the results and let you guys know.

    RF Video has value. What if you bring your Genesis to a cheap motel. Now what?
    Thats why were gonna try to improve the encoding so even RF benfits imagine a jailbar free image for all types of video output

    Problem is the PCB design and weak signals. Cut the RGB lines from the VDP and CXA side and run them with a shielded cable and you'll no longer have jailbars.
    I was thinking how this could play a role in it as well close proximity to the video ram

    Last night I got almost a stable image on my pvm-2030 but it got late and had to go to bed, this evening I am gonna finish up and post images.
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  15. #15
    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    Which encoder are you using for component? the BA6592 or the BA7230? I had several issues with jailbars and the 7230 when using very early Genesis 1s.


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