Fixing Overscan and Geometry - Odd Behavior? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 21 Old 10-14-2002, 06:51 AM - Thread Starter
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On my Hitachi 57swx20b I attemped to fix overscan and geometry.

I'll post a picture later this evening showing the grid of strings and tape all over the TV.

The overscan was fine and on the sides, I had adjusted to about 3.5% (AVIA). Then, I lined up the geometry and performed a manual convergence.

However, after the geometry adjustment, I was seeing about a 5.5% overscan on the sides (AVIA). It seems by modifying the geometry, it somehow threw my overscan out again.

Then I attempted to bring my overscan to about 3.5% again, but got an "OVERFLOW" while performing sensor initialization.. so I increased the overscan a little, fixed the geometry, and am now at 5.5% on the sides again ! :)
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post #2 of 21 Old 10-14-2002, 07:49 AM
 
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4% is ideal. Anything less and the magic focus sensors might not work correct. They are behind the edges of the screen, and need a little overscan to function.
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post #3 of 21 Old 10-14-2002, 09:02 AM - Thread Starter
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That is what I figured...

1. However, I didn't realize that modifying your geometry actually modified your overscan. After adjusting overscan, I then tweaked geometry, which threw off my overscan again.

2. Then, after fixing my overscan for the 2nd time.. I tried to fix the geometry to line up perfectly with my "grid of strings". However, I couldn't get the leftmost and rightmost lines to move close enough to the edges of the TV to line up with the outtermost strings... It seems that I hit some sort of boundary.. couldn't move the lines any further towards the edges...

3. When I then increased my overscan, I not only fixed my magic focus problem, but it also allowed me some extra wiggle room on the sides in order to bring the lines to the strings.

Hope that makes sense... interesting behavior. Anyways, I ended up with about 5.5% overscan on the sides and good geometry...
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post #4 of 21 Old 10-14-2002, 09:06 AM
 
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Quote:
Originally posted by sthong
Anyways, I ended up with about 5.5% overscan on the sides and good geometry...
Thats all that matters..:)
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post #5 of 21 Old 10-14-2002, 09:36 AM
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Overscan and geometry are directly dependent. The less overscan you set, the more difficult it will be to obtain perfect geometry and convergence. 4% (sometimes even 3 - 3.5%) is an achievable goal on most rear projectors but will take considerable effort for perfect geometry and convergence. Some sets still don't give great corner focus and convergence at the corners at 5% and need a little more overscan (I suspect this is one advantage of the SWX over UWX).
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post #6 of 21 Old 11-26-2002, 07:56 AM
 
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Quote:
Originally posted by Marc Alexander
Some sets still don't give great corner focus and convergence at the corners at 5% and need a little more overscan (I suspect this is one advantage of the SWX over UWX).
Yes- It's noticable to anyone who enters the manual service grid. The lines of the grid are smaller and tighter in the corners of the SWX than in the UWX.
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post #7 of 21 Old 11-26-2002, 10:42 AM
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Hey guys I'm having the same problem on my 51swx20b. I set the convergence and little over 1/2 of my screen on the right is fine but the left side I can't set right. Looks blurry and the blue color gives a ghost out line around the white dots like part of the screen can't focus? How do you set the over-scan? I think this sounds like the problem I'm having.

thank you.
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post #8 of 21 Old 11-26-2002, 03:23 PM
 
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NO.

Overscan is not your problem.

Focus is your problem.

Do a search...
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post #9 of 21 Old 11-26-2002, 04:54 PM
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You need to set the overscan with the AVIA test pattern. If your screen is not centered focus will be way off at the edges. Make sure of this before proceeding with any other adjustments.

It is not abnormal to have a small blue halo around the white dots (defocused blue). It just should not be very thick at all or noticeable with normal viewing material.
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post #10 of 21 Old 11-26-2002, 06:16 PM
 
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There are other overscan posts...

I have done atleast three I can recall........

use the search function.

If all else fails, click my profile and then click "all posts by this user"

start near the begining (older posts) and work forward... you'll find a few with all the info to do overscan with pictures.
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post #11 of 21 Old 11-26-2002, 10:05 PM
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So focus would be part of the geometry then? Sorry with so much talk about overscan and geometry I'm getting confused :D
I told my wife I was going to tape some strings on our tv screen and she said WHAT? So guess I should not talk about this stuff with her. :p
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post #12 of 21 Old 11-26-2002, 10:08 PM
 
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Overscan is how much of the picture is scaned on the screen Vs. how much is overscanned and not displayed (the edges)

Focus is two parts.

Electronic- easy to do with a Hitachi, only need a phillips screw driver. Focus the beam electronically...

Manual- Like it suggests, actually moving and physically focusing the lense and barrel system.
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post #13 of 21 Old 11-26-2002, 10:09 PM
 
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Forgot...

Geometry is your convergence and more specifically the overall shape of your convergence grid.
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post #14 of 21 Old 11-26-2002, 10:49 PM
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Ok thanks Mfusick :)
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post #15 of 21 Old 11-27-2002, 09:26 AM
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One thing to keep in mind when dealing with a 7" crt design is that overscan is needed because a 7" crt cannot fully resolve 1080i. If you minimize your overscan beyond an acceptable point, the edges of the upper and lower corners will visibly pincushion and cannot be corrected, no matter how much you try to overdrive the convergence board. If your set looks good with 5% or so than you are in great shape.
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post #16 of 21 Old 11-27-2002, 11:25 AM
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Quote:
Originally posted by sthong
That is what I figured...

When I then increased my overscan, I not only fixed my magic focus problem, but it also allowed me some extra wiggle room on the sides in order to bring the lines to the strings.

Hope that makes sense... interesting behavior. Anyways, I ended up with about 5.5% overscan on the sides and good geometry...
You know my Samsung behaves the same way as your Toshiba. Setting the overcan to under 5% messes up the convergence grid and I lose my perfect focus. It's kind of crazy like what comes first the chicken or the egg. I've been told just to concentrate on the geometry and forget about the convergence grid position.
My set tolerates about 6% overscan all around, the left side sensor (horizontally) is not very tolerant. That is if I move the left most vertical line too far to the right horizontally, I lose my perfect focus function. It took me some time to play with this, and makes me realize these sets are very imperfect.
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post #17 of 21 Old 11-27-2002, 01:00 PM
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Well I adjusted my auto focus. very easy and my screen is not as blurry anymore :) I still have a slight blue glow around some dots but that sounds like its normal thing to happen. Big thanx to Mfusick and sthong for all their idea's and helpful pictures. :D
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post #18 of 21 Old 11-27-2002, 03:44 PM
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Thread poster try the second URL down in my signature, it contains a web page which you should read. When on scroll down till you see Master List, white text on red background; then read to your hearts content. :)
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post #19 of 21 Old 05-01-2003, 04:28 PM
 
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Quote:
Originally posted by hob
Thread poster try the second URL down in my signature, it contains a web page which you should read. When on scroll down till you see Master List, white text on red background; then read to your hearts content. :)
What "second URL" in your signature?:confused:
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post #20 of 21 Old 05-02-2003, 10:22 AM
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Hob is no longer on this forum.

Dave
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post #21 of 21 Old 05-06-2003, 05:10 AM
 
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Quote:
Originally posted by madden
Well I adjusted my auto focus. very easy and my screen is not as blurry anymore :) I still have a slight blue glow around some dots but that sounds like its normal thing to happen. Big thanx to Mfusick and sthong for all their idea's and helpful pictures. :D
The blue halo around the white dots is your blue focus.

Hitachi's are set with lose or not exact Electonic blue focus from the fatory to make the whites bluer and brighter...

You can tighten that up a bit if you reduce your contrast and do Manual and Electronic Focus:)
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