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Dull red from a video projector

Discussion in 'Electronic Repair' started by N_Cook, Oct 17, 2012.

  1. N_Cook

    N_Cook Guest

    As though the red of the colour wheel has gone dark with age. Instead of
    vibrant red it is dull red/brown. Improved a bit with up to the limits
    changes to the colour matrix, now dull red rather than dark brown for a
    saturated red input . Not a leads problem , computer in and then computer
    out to a monitor is fine. Video source is similarly affected. No loose leads
    inside. "Service" manual has no schematic of course.
    Is there a generic cause to this as it seems quite common across different
    makes and models?
     
  2. I have no idea if it's commonplace, but the cause is likely related to the
    effect of photographs and advertisements turning magenta under exposure to
    daylight.

    The red filter is red because it absorbs green and blue light. Blue light is
    most-effective at breaking molecular bonds, as its photons have the highest
    energy. QED?

    It might also be that the designers chose a poor-quality dye for the filter.
     
  3. N_Cook

    N_Cook Guest

    Perhaps the dystuff centrifuges out to the edge ;-(
    I'm surprised these colour wheels hold together as they seem to be
    individual glass sectors super-glued into a disc.
     
  4. Is there any easy way to look at the colour wheel and see if the filter
    really is the problem.

    Could it be the lamp failing in some strange way? You can get a rough
    idea of the spectrum if there is some light spillage which has not come
    through the colour wheel (reflections coming out of ventilation slots in
    the projector, for instance). Take one of the clear CDs that is used to
    protect the bottom of a pack and, taking care not to get any
    fingerprints on the disc, hold it so that the tip of your nose is poking
    through the centre hole. Close one eye and move your head so that the
    light from the lamp appears above the top edge of the disc.

    If the light source appears sufficiently small, you should see a clear
    spectrum with a good quantity of each colour.
     
  5. N_Cook

    N_Cook Guest


    What an intriguing test, I'll make sure no one can see me while doing it,
    they may phone up the funny-farm.
    (look, the loon has taken to playing CDs with his nose)
    The lamp spillage looks normal white but
    if such a spectrum test shows an absence of red it would be useful
    elimination test. Would your "CD" difraction grating disc yest work with any
    lamp souurce for comparison say car headlight or a xenon floodlight bulb
    just to see what a complete spectrum would look like with such a disc.
     
  6. I once demonstrated it at a coffe morning of the Bath Royal Literary &
    Scientific Institution. After handing out half a dozen discs, I had a
    great time watching them trying it out (pity I didn't take a
    photograph).
    I would have thought that a normal-looking white would suggest that the
    lamp is OK - although I suppose there is a faint possibility that some
    sort of filtering or correction system could be upset by the absence of
    some parts of the spectrum which are too narrow to affect the overall
    appearance.
    It works with any source, but the image you view should be as small as
    possible if you want to see any detail of lines or holes in the
    spectrum. You can either mask-down a large source or stand a distance
    away from it.

    I've just tried the test with my own projector and the lamphouse spill
    shows a fairly continuous band with a couple of strong lines in the
    green and one in the cyan. I have tried to photograph it for you, but
    the bands don't show up:

    http://www.poppyrecords.co.uk/other/images/CBAT01_1122.JPG

    With the screen set to 'black', the residual light coming through the
    lens appears a bit stronger in the red region and the lines are not
    noticeable, so I suspect there is some correction going on.

    The light seen through one of the other vents appears to be a very
    strange magenta-ish colour (too diffuse to analyse with the CD). I
    would guess that this is coming out of the back of the lamp and is the
    unwanted transmission from a dichroic mirror.
     
  7. N_Cook

    N_Cook Guest

    The menu structure is that functions selected are designated vy changing
    blue to red lettering so are not that obvious as highlighted
     
  8. N_Cook

    N_Cook Guest

    So you replaced the cable?
    As the monitor out seems fine I assumed it could not be a cable problem
     
  9. N_Cook

    N_Cook Guest


    I suppose those discs are rejects from the pitting stage so never go on to
    the matalising stage.

    I tried with some LEDs , the most convincing was "point source" non diffused
    blue, just a slight bit of green in the spectrum with the blue. Even orange
    lens over a neon was quite convincing. The more light the less convincing
    presumably because the eye is overloaded with the most prominent allowing
    the minor spectra components to be more prominent

    Through one section of the fan louvres you can see part of the dichroic
    mirror and that is distinctly red when the lamp is on , I wonder if the
    dichroic plating? can break down over time and stop reflecting red and
    absorbing it instead, ie passing red and infra-red light.

    If I get inside again I may try mounting a piece of mirror in the lamp light
    path and try reflecting a red LED laser into the light tunnel and
    colourwheel and see if that brings up the red component/s of the image
     
  10. [...]
    Don't risk damaging your eyes, a focussed arc lamp is a dangerous
    beast*. If you can see inside with the machine switched off, it would
    make more sense to just look at the red sector of the colour wheel and
    see if it has turned brown.

    I am begining to think that the other respondents have got better
    suggestions and the problem is more likely to lie in the cables, the
    signal, or even the colour-handling software.



    * These lamps are dangerous in other ways, too. I once had to replace
    one which had burst after a cooling failure, the explosion had bent a
    0.375"-thick extruded alloy heatsink.
     
  11. N_Cook

    N_Cook Guest


    Not just the bright light , but the cooling is disrupted by removing the
    cover. I drape silicone sheet over wonen glass mat over the active area to
    obviate shatter, intense light/UV, venting pitfalls.
     
  12. N_Cook

    N_Cook Guest

    The spill over light gives plenty of red on the "difraction grating". I see
    this "blank CD/DVD" has a big clear patch on its surface, so those discs are
    rejects from the first stage of production
     
  13. N_Cook

    N_Cook Guest


    Tried another cable but the same absence of red
     
  14. Guest

    This thread is a bit confusing. To got one person talking about a color wheel and another talking about a dichroic mirror.

    The twain shall never meet. there can be a DLP without a color wheel, but it will be a three panel and it will have dichroic mirrors. Though I don't believe it has been done, there could be an LCD with a color wheel, but it would need one superfast refresh panel.

    Why don't you just post the model number.

    You have two completely different scenarios here, and one main point, is the red dull in the OSD generated inside ?

    If it is a three panel of whatever type, and the fault appears in the menus, you are looking at a fried dichroic. If it is a one panel it is most likely the color wheel but a physical inspection is warranted.

    If it only has a three section color wheel that's one thing. They just are n ot very likely to fail in that way. If they do you will see it, there should be a band where the light was. If it has a seven segment color wheel, yes it could quite have darkened but it's not all that likely.

    Incidentally one brand of these does get a fault in which the red section of the seven segment wheel breaks free and then not only is the color screwed up, the thing vibrates like all hell.

    Why no model number ? Or did I miss it ? I do believe I read the thread here. Hell, I might have the service manual on my harddrive. sure you have it,but I don't know what this thing is and we don't even know if it's a DLP or LCD or lycos or what.

    If it's a seven segment color wheel and the red looks good, it probably is in the signal processing. That is a whole different basllpark.

    J
     
  15. N_Cook

    N_Cook Guest

    This thread is a bit confusing. To got one person talking about a color
    wheel and another talking about a dichroic mirror.

    The twain shall never meet. there can be a DLP without a color wheel, but it
    will be a three panel and it will have dichroic mirrors. Though I don't
    believe it has been done, there could be an LCD with a color wheel, but it
    would need one superfast refresh panel.

    Why don't you just post the model number.

    You have two completely different scenarios here, and one main point, is the
    red dull in the OSD generated inside ?

    If it is a three panel of whatever type, and the fault appears in the menus,
    you are looking at a fried dichroic. If it is a one panel it is most likely
    the color wheel but a physical inspection is warranted.

    If it only has a three section color wheel that's one thing. They just are n
    ot very likely to fail in that way. If they do you will see it, there should
    be a band where the light was. If it has a seven segment color wheel, yes it
    could quite have darkened but it's not all that likely.

    Incidentally one brand of these does get a fault in which the red section of
    the seven segment wheel breaks free and then not only is the color screwed
    up, the thing vibrates like all hell.

    Why no model number ? Or did I miss it ? I do believe I read the thread
    here. Hell, I might have the service manual on my harddrive. sure you have
    it, but I don't know what this thing is and we don't even know if it's a DLP
    or LCD or lycos or what.

    If it's a seven segment color wheel and the red looks good, it probably is
    in the signal processing. That is a whole different basllpark.

    J

    +++++++

    The dichroic is the parabolic reflector behind the discharge lamp, letting
    through IR and reflecting visible light. 3 sector colour wheel. If I can rob
    a colour wheel from a defunct projector I will try its red sector in the
    light path of this one just to check the white areas go red etc in the
    output image.
    As putting a normal mainly white image through the projector from a graphics
    package, ramping up the red slider to 200 so the pc monitor image is redded
    out , the projector image is no change in the white areas , so I suspect
    signal processing area fault
     
  16. N_Cook

    N_Cook Guest

    This is a Mitsubishi XD200U projector. I've just taken the optical block
    apart from an InFocus LP420, RGB when viewing through the colour wheel but
    interestingly complements of cyan,yellow , magenta mirroring reflected when
    viewed at an angle
     
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