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Hey Gang!


While I was watching a DVD on my Sony 1271 via HTPC, I noticed something odd.


Usually when I watch a film there is a small amount of ambient light in the room from some recessed lighting. Last night, my girlfriend and I wanted to watch Final Destination in complete darkness (the film is tense at times).


So, during just about any scene, I can clearly see the outline of the full CRT raster on the wall where my screen is. Its like a light leak, but it is pretty uniform, almost like there is light being projected from the area outside the image area.


I double checked to see that my blanking is set, as well as making sure my brightness wasn't set too high (its set at 44).


Soooo....any ideas what this might be? Gain, Bias, Screen Volume???



Thanks in Advance!


Andy
 

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I agree with Axe.

That sounds pretty bad.
 

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Is it just on the top, bottom or all around? If you have any large air bubbles in the crt coolant chamber this can happen. Large bubbles will cause light to scatter off the bottom of the screen.


Chip S.
 

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Andy ,

-- I agree with Axe and Mark [ Chip brings another possible issue which I have seen first hand as well ] . I would bet the G2 is set too high .

-- Jason Berg
 

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Guys!


If not brightness or G2 set too high, it could be the dreaded bounce phenomenon, whereby light from inside the intended raster area of the tube face hits the first lens element, bounces back to every part of the tube face, and a little bit reaches the screen. If your projector had liquid coupled optics this would not happen, the fluid would absorb the bounce and give higher contrast ratio also.
 

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If the problem is internal light scatter you might try the following trick. It should work on most (if not all) CRT projectors other than those with liquid coupling.


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Remove lenses.


Turn brightness and contrast down so as not to blind yourself. (remember your old settings)


Display the largest image you intend to view and let the projector fully warm up.


Observe where the image is located.


Using flat-black (VERY important to be flat black) poster board, cut out a piece which will cover the face of the CRT. Cut the center of the poster board so the the image is viewable when the board is held to the face of the CRT. Take your time- remember the better your cuts the better the end results. Extend the opening in the poster board so that it is

ever-so-slightly past the CRT's image when viewed straight-on. A slightly larger opening than needed helps to compensate for drift/projector not being fully warmed up, etc. You can always experiment with the exact size, but for a starting point I would go about 1/16" The tighter your cuts are to the image the greater the possibility of edge distortion in your image. The bigger your opening, the more diminished the results will be.


Attach your poster board to the front of the CRT. A semi-permanent adhesive might be best, especially if you might change how the projector is set up down the road. Don't use tape except to "experiment" as it will slide over time and make a mess. Ive had good luck with basic white glue. In any case, make 100% sure the glue never gets near the raster --- "just in case." (we all know how "Murphy" is...) Use an adhesive you are comfortable with, as some adhesives/brands may not be removable or may potentially damage the CRT. You may need to tape the poster board in place until the glue fully dries in order to prevent a drift in placement. I used white glue because it is (normally) easily removable from glass, yet strong enough to last a long time.


Do the above procedure for all three lenses, then reassemble the projector. The convergence will most likely be off from the removal of the lenses and re-assembly, so you may need to make some adjustments. Once done, you should also notice far less light to the sides of the screen, particularly if your room is not a cave. You will probably notice blacker blacks as well.


Keep in mind this kind of trick will only solve internal light scatter issues where the reflections bounce off the phosphor. If there is something wrong in your projector it might serve only to mask (no pun) the situation.


I found the above tip from the net, but I don't remember where. I think you will find the few hours it takes to be well worth it. Ive personally only done this to the 10xx series. The results where more than impressive in both cases.



Let me know how it works for you.



Kieth
 

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I can see the raster being projected from my 9 PG Xtra as well (On to a white wall). I thought that this was normal and is why you are suppose to use dark material around the screen (border) and on the wall (curtains, felt, dark paint, etc.) to absorb this light??
 

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There are a few of ways to narrow down the problem. Here are some questions to ask:


Does the light spillage occur equally when the central image is dark or black versus when the central image is bright? If the light only spills for bright scenes, it could be caused by internal reflections of some kind within the CRTs and/or lenses.


If the light spills even on black/dark scenes, then it is probably some electronic adjustment that is out of wack, like brightness, bias, or G2.


If you are actually seeing "raster", horizontal lines, as opposed to just smooth light spillage, then your source could be errantly putting side blanking greater than "blacker than black" levels (-5 IRE or so). This is unlikely, but you never know... perhaps there is some "CRT saver" greybar mode that you got yourself in.


-Tom
 

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I've got to go with the G2 and/or brightness settings, as well. It is a very critical adjustment and being off just a little will give you a grey raster.


It's also possible that the projector wasn't set up in a totally dark room.


Vern Dias
 

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What is the best way to adj. your G2 setting? (i.e. what type of image/Raster to display)

I too have this light spilling problem...
 

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When you look into the lens you should not see any illumination outside of the raster area. If you do, then most likely the G2 is set too high.


Try looking into the lenses.
 

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Kieth: Thanks for the masking tip, though I'm not suffering from this light spilling problem myself I think it could indeed improve black levels in some extent, will try this myself for sure ;) Though I wonder how/if this will affect the cooling of the tube, or would that just be very little?
 
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