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Old 02-10-2004, 09:05 PM
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Question Retrace lines?

Hi, Gang:
I've been watching my newly-acquired Zenith 5315U roundie (chassis 24MC32) and loving every minute of it. I'm seeing a minor little problem and I'm wondering if it's indicative of something catastrophic.
When the scene fades to black, there are some thin diagonal lines at the top of the screen. Are these retrace lines? At first, they only appeared when the scene went to black, but I'm starting to see them at other times as well. In most color scenes, they aren't there--and I've looked for them!
Is this something I should worry about? Can I adjust them out? Can I just ignore them?
Thanks!
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Old 02-11-2004, 07:13 AM
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Chad Hauris Chad Hauris is offline
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It is caused by something that TV networks are inserting in the vertical blanking interval, some kind of encoded data...am not sure exactly, but it is something that did not exist when the sets were new. I see it on my round sets too and don't think it's any real problem.
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Old 02-11-2004, 07:29 AM
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As I remember the first 3 blanking periods contain data for closed caption text, this will show up on round tube sets that have the vertical set a bit on the short side. Run the vertical height up a bit to hide them.
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Old 02-11-2004, 09:56 AM
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I have noticed them on, I think, all my roundies, but only on some channels. The PBS station seems the worst. Annoying. One of the first old sets I had, a rectangular Zenith from the 60s, had retrace lines & I spent hours and hours trying to remedy it with no real success.
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Old 02-11-2004, 12:27 PM
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I get that too on my roundies and it is channel specific. If it bothers you get one of those boxes that strip macrovision and run it off the baseband video output from a VCR and then back into an RF modulator.
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Old 02-11-2004, 04:01 PM
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I know exactly what you guys are talking about as far as the coding in the signal. The retrace lines that are viewed will flash or flicker at different points througout the line.
However, I think Bob is referring to definite retrace lines, that are viewed only on a black screen, or darker scene. The retrace lines are viewed for about 1/5 of the screen at the top, and start to dissipate after about the 4th or 5th line. It seems to be noticable on ALL roundies, regardless of the channel. I dont think its a problem at all, just the nature of the design.
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Old 02-12-2004, 06:26 AM
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Chad Hauris Chad Hauris is offline
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Also you can try slightly reducing the G2 or screen controls for the appropriate color if it is the fine lines of a single color that appear when the raster is black.
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Old 02-12-2004, 08:26 AM
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Thanks!

Quote:
Originally posted by drh4683
It seems to be noticable on ALL roundies, regardless of the channel. I dont think its a problem at all, just the nature of the design.
Whew!
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Old 02-12-2004, 03:21 PM
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More modern TV sets have retrace blanking circuits to suppress the retrace lines on the screen. What is usually done is to use the flyback pulse to push one of the CRT grids or video amp tube grids to cutoff. Also the vertical retrace pulse is used. These pulses may need to be preprocessed to make sure that extranious trash doesn't get into the video picture.
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