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Dirty Screen affect?

Discussion in 'Televisions' started by bazzae123, Jan 15, 2004.

  1. bazzae123

    bazzae123
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    Just a quickie,

    Is the "Dirty Screen affect" simply that i.e. the screen is actually dirty on the inside, or is it due to some other affects. I can't understand that manufactures can produce screens that leave a residue during the manufacturing process.

    Bazza
     
  2. blindlemon

    blindlemon
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    I don't think it's dirt as such, as all the "dirty screens" I've seen have had a fairly regular pattern of "dirt" - which is actually slightly pinkinsh in colour.

    IMHO it's more likely a problem with the factory adjustment of the tube yoke during CRT setup. I expect it's done by a spotty youth with about as much interest in PQ as I have in hair gel. I also suspect that he/she is allocated about 5 minutes to do it - when it should take a skilled engineer up to half an hour. :mad:
     
  3. davej

    davej
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    My PD30 dirty screens looked like they'd tried to wash the dust off the inside of the tube but not rinsed it off properly (don't factories have to pay for the amount of water they use? makes you think.... ) so in my case I'm convinced it really was dirt.
     
  4. bazzae123

    bazzae123
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    My Philips 9528, to me, is quite bad. Every thing is OK until a scene showing a light sky is present then you can see a brownish haze on 70% of the screen, part from a patch in the centre where the picture is brighter and clearer. I have an engineer calling later to day to have a look. I've videoed all the scenes I've seen so that I can replay them. I'm interested to hear what their explanation is. Apart from that its a great set.

    Bazza
     
  5. Kula

    Kula
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    "The problem is caused by a minor error in the way the scanning coils, mounted around the neck of the tube, are steering the beam of electrons towards the screen. This may be the coils themselves, some external magetism, or some residual internal magnetism.

    Working perfectly (and few, if any do) the beam of electrons from, say, the red gun, is exactly steered towards the shadow mask so that is passes neatly through the corresponding holes in the mask and lands on the red (say) phosphor spots on the screen itself.

    Working less than perfectly, the beam of electrons does not hit the shadow mask in exactly the right place and part of the beam is absorbed by the mask. Only the remaining part hits the screen and the phosphor is thus illuminated somewhat less than it should be. Hence a dark patch.

    Working even less well, and the beam passes through the wrong hole in the shadow mask and lands on the wrong phosphor. So, for example, the red signal actually (partly) illumintates, say a blue phosphor. And this is what causes colour staining.

    So, colour staining is the same problem you have, made worse.

    It can be fixed by a competent and experienced engineer, who can affix small permanent magnets to the neck of the tube, to correct any mis-steering of the electron beams.


    __________________
    Formerly known as LV426"
     
  6. Kula

    Kula
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    Let us know how u get on - if an engineer can come out and solve the problem without taking the set away that would be cool.
     
  7. LV426

    LV426
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    Kula - thanks. Saved me the job.
     
  8. Kula

    Kula
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    :)
     
  9. Kula

    Kula
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    How did u get on with the engineer?

    Did he manage to fix the problem?
     
  10. bazzae123

    bazzae123
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    No he didn't repair it. He just filled out a piece of paper and said go to the local store, or web site, and arrange for your money back, or get a replacement. So, do I get a replacement, or try something different. Decisions, decisions.

    Bazza
     
  11. RocketNige

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    I'm on my second Panasonic 32" PD30, and the dirty screen is driving me up the wall. I don't think, in my case, it can be caused by this scanning coil error. Reason: I turned the set off and directed a pure white picture from an LCD projector onto the screen (it was the only source I had which was uniform and intense enough to do this with). Result: even in reflection, I can see irregularities in the coating on the tube, which match up exactly with the dirty patches I see when the TV is on. Doesn't this rule out the coil explanation? (Genuine question - I don't know enough about the mechanics of these things to know for sure).

    I bought the 1st set on Dec. 20th - had it exchanged for unit number 2 in late January. Too late to get another exchange or refund now?
     

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