Burnt polarizor in an LCD video projector

[N_Cook]

Well errupted if not burnt. The other 2 polarizors and LCD panels look
fine. This one is opposite a frame for its LCD , made of aluminium, that
seems to have corroded , or at least loads of white powder on and around
it.
http://diverse.4mg.com/polarizor.jpg
over some squared paper.
Could an excessive amount of dust on the polarizor surface have caused a
local hot spot, or some chemical process going on.
Robbing a polarizor from a 7 segment display and crossing with one of
the other projector polarizors gives a plum colour, wheras 2 of the
original are brown. I suppose better than the disrupted spidery
discoloured image before, a different colour cast in the "blacks"

[jurb...@gmail.com]

Betcha it's the blue. For some reason I see mostly the blue go bad in those. It probably has somethig to do with the wavelength of the blue light, though of course any of the could go bad first depeding on how the light engine is dsigned. Depends on the air flow through it and a few other things. Like if the filters were ever cleaned.

Shit like this is why I never recommended LCD projectors. If the manufacturers would supply light engie parts it would be different but they don't have to in the US so obviously they don't. Make ya pay twice what the thing is worth for the whole assembly. Should be illegal but, well not really. It would be unconstitutional. ?But then with the second amendment we could shoot the fuckers.

If you are going to replace it, you must determine the orientation. It is absolutely critical for getting the contrast ratio. You have to get the new one in front of the old one and see at what angle it is the most opaque. Then you must find a way to tunr it 90 degrees as accurately as possible. I mean within like a degree or two. Otherwise part of the curve will invert, and blacker will become whiter, or whatever color it may be in that channel. Don'r count on it being the same as any other channel, they could all be different as easily as the same.

I almost did a job like that once. I pondered using a plarizing filter made for photography but if it's glass it changes the focal length. You cannot adjust the focus indenendently as far as I know, so you are stuck with plastic. Hope it can take at least the same abuse as the original. That might be special high tmeperature material or someting and the one robbed from an old numeric display maght fail quickly from the heat. I do not know. It's just a bitch when you do al that work to have it fail in a week, and with no better solution. Or use a glass one ad put up with a little defocus in - wellllll

If it is the blue, it woul probabvly be the most tolerablt. Because o the colorimetry, the focus of the red and green are alot more critical. In fat, many RPTVs had the blue slightly defocussed on prupose to cause raster line fill in for better efficieny. Sony did this, and the reason they had to do this is because their blue CRTs had a deeper blue phosphor. Other units, the blue simply was not as blue because of the phosphor and the imbalance of efficiency was not as much.

If the blue is slightly polluted with white, or is a longer wavelength it is more efficint, but then the unit is limited in just how blue of a bli=ue it can porduce, and it DOES make a difference in image quality. One that some manufacturers are willing to sacrifice more than others.

In an LCD projo, rather than the phosphor determining this, the dichroic mirros make all the difference. I imagine pushing for a purer blue or a higher wavelength blue taxes it and makes it fail first.

That's why I would be surprised if your problem is not in the blue channel.

I'm sure you'll tell if it isn't.

Either way, hang on to that original part to get the orientation. That's what happened to the job I didn't do. I did not do the disassemble and they only had piece of the original polarizer. That graph paper might be a good way to accurately turn the new filter exactly 90 degrees.

I would like to ask (and I do not want the "proper" spelling of "Phosphour" here (lol) is that paper with the squares on by chance sized so that there are four squares in 2.54 cm square ? Here, it is four squares to one inch. I wonder if they just make it the same. I remember buying metric alen wrenches and they were like 1.27, 1.54 and shit. I thought to myself, shit, I woder if they are the same size as US inches.

Of course they weren't, but it seemed like the sizes were so arbitrarily chosen - why bother ?

[N_Cook]

On 15/08/2014 22:21, jurb...@gmail.com wrote:
> Betcha it's the blue. For some reason I see mostly the blue go bad in those.. It probably has somethig to do with the wavelength of the blue light, though of course any of the could go bad first depeding on how the light engine is dsigned. Depends on the air flow through it and a few other things. Like if the filters were ever cleaned.

With all that dichroic stuff around , I don't know how to tell RG&B but
a blue dot on its LCD ribbon.
It is nice not to have the whine of the colour wheel of DLP projecors.
I'd marked the position of the single mounting and positioning screws of
each polarizor before removing. The circular form of the edge of that
holder and about +/-5mm of adjustment available but all 3 were in the
middle of the slot

[N_Cook]

Its a Philips SV2 LC3132 from 2003
The paper squares are 5mm
I've only played with DLP types previously

[N_Cook]

confirmed blue path one, I replaced the lamp with a torch

[mrob...@att.net]

N_Cook <div...@tcp.co.uk> wrote:
> Could an excessive amount of dust on the polarizor surface have caused
> a local hot spot, or some chemical process going on.

Since maybe the late 1990s, a lot of video equipment (including the
projector itself?) seems to default to a blue screen if there is no
input / media present. Maybe somebody left it running in the "blue
screen" condition for an excessive amount of time?

Matt Roberds

[jurb...@gmail.com]

>"Since maybe the late 1990s, a lot of video equipment (including the
projector itself?) seems to default to a blue screen if there is no
input / media present. Maybe somebody left it running in the "blue
screen" condition for an excessive amount of time? "

This is not CRT technology.

The light is produced at maximum all the time by the lamp. The picture is produced by blocking it. As such, NOT blue would tax the system more than blue. If the screen is black, most of them waste more power, make more heat for the simple reason that the light is not allowed to pass.

I remember in the CRT days we got some bad blue tubes in RPTVs. In some brands I figured out it was because they wenyt to an RMS type of detector for beam current limiting. Since the blue was always driven harder, and collective detection of beam current would allow more blue beam current.

Alot of VCRs did that blue screen thing, not always the TV. People would fall asleep and their video tape movie would end. Made me money actually. The most frequently changed tube in those things was the blue. I did hundreds of them.

[jurb...@gmail.com]

I need to elaborate a bit.

This is the polarix=zing filter. It is not something that MORE blue light passes through when blue is on the screen. It's function is to BLOCK the blue light that is anti-polarized from its axis when blue on the screen is not desired.

[Cydrome Leader]

I thought the blue tubes just had to be driven way harder to get the
required brightness. Do you know if this is true, at least in RPTVs?

[jurb...@gmail.com]

>"I thought the blue tubes just had to be driven way harder to get the
required brightness. Do you know if this is true, at least in RPTVs?"

I THINK, on a molecular level that because the blue has a shorter wavelength, it posed the same problems as it did when LED technology came up. You are sending BLUE light through there, not RED or GREEN which are longer wavelengths.

It is hard to explain sghort. It has to do with the fact that higher frequency wavelengths have an inherent higher energy.

This is beyond the scope of this group and its intent.

I think.

Is it really ? Electronics is a part of science.

But...

[N_Cook]

Another point to consider is there is no sign of the LCD problem on any
of the 3, often seen with DVM say, when left in bright sunshine, and
black bleeding across the screen. Is the construction of these tiny
projector LCD arrays a different construction and the crystal cannot
bleed out of well if overheated?

[N_Cook]

Back to a good blue background (for how long as just ordinary low temp
LCD display polaising film transferred) , not tried a video feed. Going
through menu info , the white text is clear but there are displaced
minor ghost colour images of the text, like the CRT type of projector
with out of adjustment colour feeds. How come there is good white but
also displaced images.

[N_Cook]

Someone had been in here before. Each of the 3 LCD holders is held to a
steel frame with countersunk head , perhaps 1.5mm machine screws , in
countersunk holes of the subframe. 3 corners only, the fourth not having
a tapped thread in the mount. But one of these 3 screws was missing and
one of the 3 on another LCD was loose. I assume a tinkerer had played
with them. Countersink arrangements , however precise , I cannot see
being precise enough for sub-pixel alignment of a 1cm or so diagonal
LCD. The combined LCD holder and its subframe is held to another frame
combining all 3 . Each subframe has 4 pins and located in 4 holes of the
overall frame and the holes filled with epoxy or something like that.
Would that be where the precision alignment on a factory jig would occur?
The only way I can see of getting anywhere near any re-alignment is :-
There is a little space to fiddle with the red and blue frames through
available aperatures and align them to the green one which is
unaccessible, so keep that one fixed where it is. With the provided
countersunk screws and pits, that will not work. Perhaps temporary
longer cheesehead screws and springs under each would give enough suck
it and see and then stay in place manoeverability .
Perhaps a dab of epoxy on each of the 2 corner screws would be enough to
keep in registration , while removing the optical block , without the
flimsey ZIF ribbons dislodging the frames, then fix more permanenly.

[N_Cook]

Found a replacemnent countersunk screw but misaligned image
Blue displaced 8 pixels rigth and 1 down
Red 10 right and 8 up.
May as well have a go with sprung small screw temporary replacements,
can't make the situation worse. At least the misalignment seems to be
vertically and horizontally consistent, just displaced parallel.

[Cydrome Leader]

much much reassembly is required between each adjustment and testing the
alignment of the LCDs and other junk in optical path?

this project sounds pretty long.

[N_Cook]

I like a challenge, it was thrown out anyway. What is the saying ? "The
difficult is done at once; the impossible takes a little longer"

[Cydrome Leader]

Ha.

I offered to fix a camera recently that served no other purpose other than
to learn or something I didn't pay for.

[N_Cook]

Even better if you make a repair brief for the interweb thing, even if
just how to get inside things

[Cydrome Leader]

I've been thinking about this for a while in fact. The problem is making a
video is almost more work than any repair, and working solo makes it even
harder. If I can come up with more space for a new workbench there may be
a chance of this.