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The UAV Rev. D Video Upgrade Thread


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#276 Bryan OFFLINE  

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Posted Yesterday, 5:23 PM

Been looking at the 1200XL's video. Atari added a color boost circuit to the 1200 series which makes the burst about half the amplitude of the chroma across the rest of the line. This has the same effect as cranking the Color control on the monitor since the burst defines the reference amplitude. The burst is extraordinarily weak, being about 1/3 of the proper amplitude (@ ~100mV). All other chroma is about 200mV. The chroma is also messy looking. This weak burst means the monitor will increase its internal chroma gain to compensate which causes a lot more color artifacts.

 

In addition, the sync signal is also very weak so some modern sets won't sync at all and the darker shades of gray probably won't show up. Atari really botched this one, but I do want to experiment with the color boost concept.

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#277 DrVenkman OFFLINE  

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Posted Yesterday, 5:36 PM

Been looking at the 1200XL's video. Atari added a color boost circuit to the 1200 series which makes the burst about half the amplitude of the chroma across the rest of the line. This has the same effect as cranking the Color control on the monitor since the burst defines the reference amplitude. The burst is extraordinarily weak, being about 1/3 of the proper amplitude (@ ~100mV). All other chroma is about 200mV. The chroma is also messy looking. This weak burst means the monitor will increase its internal chroma gain to compensate which causes a lot more color artifacts.

 

In addition, the sync signal is also very weak so some modern sets won't sync at all and the darker shades of gray probably won't show up. Atari really botched this one, but I do want to experiment with the color boost concept.

 

Wow. You're not kidding. I'd be interested in seeing what Bob Wooley's ClearPic mod does to that, and also how the UAV output compares on the scope.



#278 irich2 OFFLINE  

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Posted Yesterday, 5:48 PM

Bryan,

 

Payment sent to your PayPal.me account.

 

Thanks!



#279 Bryan OFFLINE  

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Posted Yesterday, 6:34 PM

Wow. You're not kidding. I'd be interested in seeing what Bob Wooley's ClearPic mod does to that, and also how the UAV output compares on the scope.

UAV samples of the same signals plus the NTSC and PAL standards. For NTSC, burst is specified as +/- 20 IRE and for PAL it's +/- 21.43 IRE. For NTSC, 1 IRE is 7.14mV. For PAL it's 7mV.  So, the NTSC burst is ideally 285.6mVp-p and PAL is 300mVp-p. UAV (Rev D) is about 288mV which is close enough. Sync is defined as 286mV for NTSC and 301mV for PAL. UAV is about 312mV because NTSC has a separate black level at 339mV.** This means LUM 0 is a touch above standard black for PAL and a touch below it for NTSC. A LUM of 1 is above black for both. Most Atari video is far enough away from the standard that either the lowest shades are lost, or the background is perpetually gray.

 

** The blank level isn't technically required by consumer equipment and although Atari included a pin for it in TIA, they didn't end up using it to create a separate Luma step. Instead, they sometimes used it to implement a chroma boost like the 1200XL has.

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#280 Bryan OFFLINE  

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Posted Yesterday, 11:17 PM

By the way, you can order UAVs specifically for 1088XEL use and they'll come with down-facing pins instead of the terminal.

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