Zenith E44W46LCD Polarizers

On Sun, 28 Jan 2007 11:07:58 -0800, Andy Cuffe Has Frothed:

I doubt a polarizer from a CCFL would stand the heat. I read some stuff about your set in this forum. Have a look.

I got the same problem in one a bit older and bigger.

I've studied the theory of operation and there is a BIG BIG problem changing polarizing filters. Orientation.

If you get it 90 degrees off the color affected will appear in negative. Anywhere in between no amount of gamma correction will fix it.

If we assume, and are correct, that the polarization is along the plane of either the vertical or horizontal boundries, we achieve a

My unit appears to possibly use more then one for the blue channel. The filter is gone, and everything that is supposed to black is blue. But then there is some modulation. See nowhere in the actrive video can it produce white. It gets the dingy brown, except for in the menus.

PTVs have long had problems with blue. It was dealt with many ways in CRT days. A blue push circuit, Sonys used a controlled defocus.

Of course these things are a different animal. But blue is still blue, and I believe it is still a problem for engineers. It is probably because of it's short wavelength. In an LCD, the blue is obviously hotter, as anything that passes blue has to absorb or reflect everything else, including heat and IR, which are at the opposite of the visible spectrum.

I'm sure that the polarizing filter from a camera shop would probably work, but which way does it go in ? The material itself is not hard to get.

It appears that they glued the material to glass to provide some thermal damping. But on glass, it obviously didn't work very long.

For reasons like this I highly advise customers against buying any LCD based PTV. Even DLPs melt the color wheel. It is just too damn hot.

Actually your symptom doesn't sound like the primary polarizing filter for the blue channel, but these wild designs do make troubleshooting by symptom difficult at best. Why can my Zenith display white only on the menus ?

LCD technology is fascinating, but IMO is not ready for the mass market. It just ain't ready,. polarizing filters should be available like light bulbs and air filters. They probably never will be.

The main question, if we intend to replace polarizing filters is, once the light comes out of the lens is it still polarized ? If so we can determine the axis at the light output. Follow the light path backward and figure out which way to put it in. I don't see any other way.

JURB

I took the filters out today. The green and blue filters are definitely damaged. There is a very noticeable rectangle in the middle of both bad filters.

Using a sheet of polarizer from a bad LCD display and rotating it until the TVs filter goes dark I could see that the faded part is not completely polarizing the light any more. The blue is also a little dark in the middle. This explains both symptoms with the picture.

Figuring out which way to cut the new filter isn't a problem. You just put the old filter on top of the new one (so the glass is NOT between the old filter and the sheet of new filter). Then rotate it until it's as clear as possible. Then it's just a matter of cutting the new filter.

I tried it with this LCD screen filter and it worked surprisingly well. Blacks are much better than with the original filters. The only problem is that the filter plastic I used doesn't pass as much light as the original stuff. The whole picture is about half as bright as it used to be. It's still an improvement since black is better and there's no tinting to the picture.

I ran it for about 3 hours and it seemed to hold up. If I can find a more efficient polarizing filter I think this could be a practical repair. Andy Cuffe

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Bravo, you've made more progress than I have.

I understand that orientation can be determined the way you did, however in my case the filter had already been removed by the time I got to it. Thus my problem.

Is what you used a polarizer from a direct view LCD ? If so I think that explains the lower transmission, it probably has some anti-glare or anti-reflective properties that are not needed in a PTV.

Problem is I think the new filter(s) are going to run hotter due to those properties.

I think we will be able to repair these things if 1, we get them while there is still some of the original filter to determine orientation and 2, obtain the high transmission polarizers.

Oh, I forgot number three, have the hands and skills of a microsurgeon and quit drinking coffee three days before working on them. For a fraction of the pay I might add.

Mine is coming back when the work slows down. We can barely keep up right now. Actually I am surprised I wasn't handsomely bribed to work today, with super bowl Sunday coming tomorrow. But I have this policy of not working Saturday anymore so, this would have to be one sweet bribe, and I think they know it.

Anyway, if you have a lower light output than before, I think it will burn up faster than the original. I don't think you can really call it repaired. If it burns up in a few months, the customer will blame you, not the manufacturer. I could say it right now, the filters should all be glass, or embedded in glass, not glued on like a decal. In addition, I believe the manufacturers know of this limitation.

Congrats on making progress on this, but that doesn't solve my problem. I still have the burning question, is the light still polarized at the lens output ? If so, with it running, when the blue blacks disappear that is the orientation. With a bit of mental gymnastics, looking at which way the mirrors go in the light engine, I think I could make a heck of a good guess.

JURB

I agree that these filters probably won't last, but it at least proves that they are the only problem with the projector. I think you can get polarizers for theatre lights. They should be designed to take some heat and might work.

On this projector, it has maximum transmission when the projector is off, so I could find the correct orientation by rotating the new filter while looking through an LCD panel. The design of the optics make this easy, but it might be impossible of other projectors. Andy Cuffe

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I work for an LG service center in the Twin Cities. In fact as of three weeks ago we awarded the the number 2 LG service center in the nation. All that to say that the polarizers are available from a LG authorized service center but most wont sell them over counter. The blue IS the most common one to go. The others usually have no problem. Our cost on a 52 which had the same problem was aroun $120. Good luck! The best would be to bring to a LG service center.

Later..

Do you have any idea where I could get these? I need both the green and blue. Andy Cuffe

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