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 Post subject: Jailbars on NES front-loader... cause and fix?
PostPosted: Fri Dec 09, 2016 9:54 pm 



Joined: 23 Dec 2015
Posts: 170
My front-loader NES is giving vertical jailbars on solid green, blue, or brown backgrounds. They aren't noticeable on white or red. The curious thing is, I get a blue screen if I turn on the NES without a cartridge inserted, but there aren't any jailbars there at all. Only when playing games.

At first thinking it was a PPU issue, I swapped consoles. However, the one I swapped to is doing the same thing, maybe not quite as strong. Both consoles have the ALPS video block instead of Mitsumi. Now, I did some quick googling, and discovered that this MIGHT be an issue with a lot of front-loaders: https://forums.nesdev.com/viewtopic.php?f=9&t=13086

Now a user on Nintendoage was experiencing wavy lines/diagonal noise with his front loader, also with a ALPS video block, and fixed it by soldering in a 0.1uf capacitor: http://nintendoage.com/forum/messagevie ... adid=18909 Could this technique potentially get rid of the jailbars? If so, it could be a good discovery. (We're talking composite output only here, I'm guessing any HDMI or RGB mod will bypass this entirely.)

Anyone else experience this?


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 Post subject: Re: Jailbars on NES front-loader... cause and fix?
PostPosted: Sat Dec 10, 2016 6:52 am 


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Joined: 10 Jan 2014
Posts: 539
Location: USA
It's typically address line interference. This is most prominently found on CPU-10 and CPU-11 boards. CPU-07 and CPU-08 revisions fare better.

You can mitigate those vertical jailbars by lifting pin 21 (composhit) out of circuit and terminating it off the board.

Bypass caps an help take some of the edge-off, but it isn't quite as effective as pulling composite off the board and terminating it away from those routes.
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 Post subject: Re: Jailbars on NES front-loader... cause and fix?
PostPosted: Tue Dec 13, 2016 12:02 am 



Joined: 23 Dec 2015
Posts: 170
Voultar wrote:
It's typically address line interference. This is most prominently found on CPU-10 and CPU-11 boards. CPU-07 and CPU-08 revisions fare better.

You can mitigate those vertical jailbars by lifting pin 21 (composhit) out of circuit and terminating it off the board.

Bypass caps an help take some of the edge-off, but it isn't quite as effective as pulling composite off the board and terminating it away from those routes.


Well, adding the 0.1uf cap did absolutely nothing to mitigate the jailbars (unless I should add it in a different position than what the guy on Nintendoage did.) So now I'm just going to look for an early revision board.


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