Fixing the scan area - AVS Forum
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post #1 of 4 Old 04-04-2002, 05:06 PM - Thread Starter
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I have an old 27" Toshiba CRT and the picture has drifted towards the top to the point I can easily see the overscan area on the bottom, but cannot read the text in the top line while pulling up my info on DirecTV. Is there any way to adjust these, similar to what is done for RPTV sets?

Thanks,
Mike
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post #2 of 4 Old 04-04-2002, 05:22 PM
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In principle, yes.

You'll need to get an estimate from a local TV repair shop.

Unfortunately, that substantial a vertical deflection circuit adjustments in a consumer TV has to be done with the case open and lethal voltages exposed. These adjustments should only be done by trained technicians with the appropriate tools. So much drift may also require replacements of components that have aged out of spec.

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post #3 of 4 Old 04-05-2002, 12:55 AM
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I also have a question about overscan rates. Fortunately I have a TV with a service menu so I can adjust from the remote.

I am having my 40" Sony calibrated tomorrow by a local ISF certified technician, and the last time I spoke with him, he seemed to think we should set the picture at 5% overscan rate.

While I agree this works well for OTA broadcasts, videogames, etc. I am pretty sure that most DVD's and LD's that I have extend to the full available size (0% overscan rate) to get to the OAR (original aspect ratio).

Am I mistaken? If not, what's the general comprimise? 5% or less?

Thanks!
-Matthew
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post #4 of 4 Old 04-05-2002, 04:02 AM
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A 5% loss of image around the edges won't noticably affect the image aspect ratio. In many cases it's a reasonable compromise.

Unfortunately, many video sources (not DVDs) assume that the viewer's screen has significant overscan. Many TV channels include junk at the edges of the image: some programs have timing and other video control signals visible there. Some cable TV boxes don't provide chroma for the full width -- the edges of the image are grey instead of colored. If those kinds of anomolies are too distracting for you, a small amount of overscan is a very good idea.

The standard reason for having overscan is to compensate for future drifts in the video retrace circuitry. If the image originally exactly filled the screen and if future drifts were to cause the picture to shrink, you'd start seeing dark borders.

Contrarily, if you have the set adjusted so even the corners of the image are visible, there will be slight black boarders at the edges. CRT phosphors do fade with use. If the image gradually expands, those edges will be slightly brighter. This could be quite distracting.

Personally, I dislike the idea of having parts of the image hidden from me: I prefer slight dark unused boarders on the CRT. I use a computer monitor for direct viewing of video sources, though, so size adjustments are trivial.

I hope these considerations help you decide what's appropriate.

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