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RogueChili
Joined: 31 Mar 2008
Posts: 162
Location: Westfield, MA
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| Posted: Fri Aug 28, 2009 3:57 pm Post subject: INFORMATION REQUEST |
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I found a secondary problem with the video circuit in the 1292 and would like to know if other model projectors suffer from this problem.
What I found is a shadow following a long bright horizontal bar.
The best conditions to test for this are:
• Set projector brightness to 100 percent
• On a black background, project a white horizontal bar centered on the y axis; the length of the bar should be 50 percent of the raster width; the height is not important
• Looking at the tube face observe the area following the white bar looking for a slightly dark shadow extending to the edge of the raster.
Please let me know what you find.
Thanks
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Fri Aug 28, 2009 10:08 pm Post subject: |
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This is a design issue with the 1292 and some other sets. One of our members has a fix, see a different thread here..
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RogueChili
Joined: 31 Mar 2008
Posts: 162
Location: Westfield, MA
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| Posted: Fri Aug 28, 2009 10:44 pm Post subject: |
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Does the fix require high elevation and an open window?
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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RogueChili
Joined: 31 Mar 2008
Posts: 162
Location: Westfield, MA
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| Posted: Fri Aug 28, 2009 10:56 pm Post subject: |
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:thumbsup:
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Fri Aug 28, 2009 11:28 pm Post subject: |
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Is this the black bounce issue?
There are two issues I know of with the 1292:
1. Streaking
2. Black level bounces around.
I thought they might be related, but I know squat about a 1292's guts.
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Fri Aug 28, 2009 11:31 pm Post subject: |
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Oh, and a NEC will do this black shadow after white as well. And given the right circumstances an XG will streak. Just not as bad as a 1292.
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RogueChili
Joined: 31 Mar 2008
Posts: 162
Location: Westfield, MA
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Fri Aug 28, 2009 11:35 pm Post subject: |
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Bloody hell, stop posing links to mystery dirt cheap electronic stuff. I'm sooooooooo tempted! 
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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RogueChili
Joined: 31 Mar 2008
Posts: 162
Location: Westfield, MA
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| Posted: Fri Aug 28, 2009 11:52 pm Post subject: |
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Only additional info the seller has is he thinks they are made by Panasonic
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Fri Aug 28, 2009 11:54 pm Post subject: |
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I've asked for some more pix of the units. Looks like nothing I've seen before.
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Sat Aug 29, 2009 12:04 am Post subject: |
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I want one! Who's in for a drive and owns a truck? lol
_________________
Tech support for nothing
CRT.
HD done right!
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Sat Aug 29, 2009 12:48 am Post subject: Re: INFORMATION REQUEST |
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| RogueChili wrote: | I found a secondary problem with the video circuit in the 1292 and would like to know if other model projectors suffer from this problem.
What I found is a shadow following a long bright horizontal bar.
The best conditions to test for this are:
• Set projector brightness to 100 percent
• On a black background, project a white horizontal bar centered on the y axis; the length of the bar should be 50 percent of the raster width; the height is not important
• Looking at the tube face observe the area following the white bar looking for a slightly dark shadow extending to the edge of the raster.
Please let me know what you find.
Thanks |
One possibility is the video drive "undershoots" after a long white bar when it makes the black transition. That can cause a dark "shadow" after the white bar. Break out the scope and look very closely. Cathode drive will be inverted from the pic.
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Sat Aug 29, 2009 1:08 am Post subject: |
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Yes, that is what NECs do.
It's not surprising when you graph out the infinite bandwidth path the video has to follow.
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RogueChili
Joined: 31 Mar 2008
Posts: 162
Location: Westfield, MA
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| Posted: Sat Aug 29, 2009 1:37 am Post subject: |
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What I have seen is similar only the slope of the white level (top of pulse) increases during the sweep. Another interesting point is that the brightness level slowly increases with each scan line as if the clamp voltage is slowly increasing.
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RobertMfromLI
Joined: 29 Jun 2009
Posts: 114
Location: West Islip, NY
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| Posted: Sun Sep 06, 2009 5:13 pm Post subject: |
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| Curt Palme wrote: | | I've asked for some more pix of the units. Looks like nothing I've seen before. |
It reminds me of the guts for a tabletop/rear projection projector (like used in various game consoles and odd computer applications) or fixed screen old style projector.
My guess is that this was used in an outdoor movie theater for ad projection, in which case, it's likely CRT if it is as old as it looks. I've seen a few but recall little to nothing about them.
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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| Posted: Sun Sep 06, 2009 7:15 pm Post subject: Re: INFORMATION REQUEST |
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| tse wrote: | | RogueChili wrote: | I found a secondary problem with the video circuit in the 1292 and would like to know if other model projectors suffer from this problem.
What I found is a shadow following a long bright horizontal bar.
The best conditions to test for this are:
• Set projector brightness to 100 percent
• On a black background, project a white horizontal bar centered on the y axis; the length of the bar should be 50 percent of the raster width; the height is not important
• Looking at the tube face observe the area following the white bar looking for a slightly dark shadow extending to the edge of the raster.
Please let me know what you find.
Thanks |
One possibility is the video drive "undershoots" after a long white bar when it makes the black transition. That can cause a dark "shadow" after the white bar. Break out the scope and look very closely. Cathode drive will be inverted from the pic.
Scott |
My BG808s with 120MHz rgb amps (no overshoot streaking) have light undershoot after long white bar. My BG500 had it, streaking modded 801s have it and same thing with BG1200. It can only be seen with test picture or windows over desktop in pc picture.
I have been called it negative streaking, since it does lower black level.
I made this test pic some time ago, it have also black bars to see what it causes to gray level.
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