gradual screen darkening???

Discussion in 'Displays' started by Roger-L, Apr 1, 2005.

  1. Roger-L

    Roger-L Auditioning

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    Screen Problems on JVC i'Art Av-30W585 where after a few hours of operation, the image gets progressively darker. Anyone experienced this on CRT's before?
     
  2. John S

    John S Producer

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    It would almost have to be a power supply issue...

    I have seen general power grid brown outs sort of cause the same symptom though.
     
  3. Roger-L

    Roger-L Auditioning

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    John, I had briefly considered that but the set is on a separate, conditioned line. I'm thinking it's somehow related to the unit heating up during normal operation - either the tube or the powersupply might be getting overheated? But the set is on an open shelf with plenty of circulating air. The unit's only a month old. I'll guess it's time to have JVC make a service call to see what they think.
     
  4. John S

    John S Producer

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    Well, I see your in Westchester, NY.. Notorious for brown outs....

    best of luck with it.
     
  5. Jay Taylor

    Jay Taylor Supporting Actor

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    When you are experiencing this problem you can measure the AC line voltage with an AC voltmeter to determine if the problem is a brownout.

    If brownout is the problem you may get a decent UPS for your TV set that will maintain constant AC voltage during most brownouts. However, unless you purchased a monster sized UPS I wouldn’t power your surround sound system with one. Playing at reference level your sound system needs a lot of current that a UPS may not be able to supply.
     
  6. Leo Kerr

    Leo Kerr Screenwriter

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    Classically, in brown-outs, the image shrank.

    I haven't tried it on a 'modern' set, though.

    Anyway, this sounds to me like a problem internal to the set, and it's probably a $0.35 electrolitic capacitor going bad.

    A sort of side question is,
    if it dims down to, say, half brigthness, and then you turn it off. How long do you need to wait until when you turn it back on, it's full brightness?

    Leo
     
  7. Roger-L

    Roger-L Auditioning

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    Leo, I agree that it sounds internal. It takes approx. one hour of "off-time" for the image to restore to "normal" after which it begins dimming again after another 1-2 hours of use.
     
  8. Leo Kerr

    Leo Kerr Screenwriter

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    Somebody's gone heat-sensitive.

    Might not be a cap, though - I have a hard time seeing how they'd get heat sensitive, so I'll change my guess to a $0.45 transistor.

    leo
     
  9. Jay Taylor

    Jay Taylor Supporting Actor

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    Have the power supplies in this type of set gone modular like computers?

    If so, the fix may be to replace the power supply module or whatever module is defective even if the bad component in the module costs 50 cents.
     
  10. Leo Kerr

    Leo Kerr Screenwriter

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    The last CRT sets I looked into were quasi-modular. They weren't a neat "box" like a computer's power supply, but were boards on mounting points with cable harnesses connecting them around.

    Some modules are probably pretty easy to replace. My Sony CRT at home, however, has a small board on the very back of the CRT itself, and I suspect that one would be very difficult to do.

    The catch is, it's not entirely clear which board might be going bad.

    It could be the input card, a power supply card, or the drive card. (Unfortunately, the drive card is, in the case of my set, the one on the back of the tube!)

    Leo Kerr
     
  11. Roger-L

    Roger-L Auditioning

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    Going to let JVC have a look-see and will report back on their conclusions. Could be something's not properly isolated back there and as the CRT reaches higher operating temps there's some interference. Kind of aggravating since, to paraphrase Ogden Nash, when the pictures good, it's VERY good. And when it's bad, it's awful.
     
  12. DonRC

    DonRC Stunt Coordinator

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    Yeah, they'll do it to you every time... You ask a question and they lowball the price, only to see it rise dramatically (errr...) as time goes on... [​IMG]
     
  13. Leo Kerr

    Leo Kerr Screenwriter

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    yeah, but wait 'till you see what JVC does to the price!!!
     
  14. Roger-L

    Roger-L Auditioning

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    sure, 'cause to them it's the space shuttle. No such thing as a $0.35 part. I can't wait for the verdict.
     
  15. Roger-L

    Roger-L Auditioning

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    UPDATE: JVC repair came today. Acknowledged the problem but said he couldn't give definitive diagnosis without getting it on the bench. He says he suspects the problem is the flyback. Took it to shop and said don't expect it back for at least 2 weeks because since it's a new model, he might not have the necessary part(s) on the shelf.
     
  16. Leo Kerr

    Leo Kerr Screenwriter

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    The interesting thing is there are still some shops that do component-level work.

    We had a CRT front projector (Sony 1215 comes to mind, but it doesn't sound right, either,) start going wonky. We sent it out to a local shop for service, fully expecting a $1500 parts, $500 labor charge to replace the Red electronics.

    Ultimately, it came back as about $200 labor, ~$15 parts.

    But, bet of luck to you.

    Leo
     

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