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Sony TV brightness/tint glitch

Discussion in 'Electronic Repair' started by zmike6, Jul 26, 2004.

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  1. zmike6

    zmike6 Guest

    I've just started having a problem with a Sony TV, model KV27V20 (27",
    direct view, V-series) which is about 6 or 7 years old. The
    problem(s) appeared suddenly today. Black levels have become much
    more bright (gray), and the colors have taken on a bluish tint. The
    blue tint is not overpowering, but it gives blacks a bluish glow, and
    reds look a bit magenta. Adjusting tint doesn't really help. Whites
    and yellows are less obviously affected by this strange blue effect.
    The grayish blacks combined with the blue tinge gives the picture a
    flat lifeless appearance. Input doesn't matter, DVD/VCR/cable all
    show the same effects.

    I can make the picture look tolerable by greatly reducing the
    brightness, but then I lose a lot of picture detail. Something
    clearly has gone amiss, any ideas or suggestions?
     
  2. Jerry G.

    Jerry G. Guest

    Most likely, the CRT is starting to go weak. The electron-guns are starting
    to loose emission, and the AKG circuits are running out of range to maintain
    the colour balance, and proper biases for the electron-guns in the tube.

    If you have a DVM, and know what you are doing, it is possible to check the
    bias levels at the tube socket, but it is rare that I have seen faults in
    the drive to the tube. Considering the age of the set, I am betting on the
    tube failing.

    --

    Jerry G.
    ==========================


    I've just started having a problem with a Sony TV, model KV27V20 (27",
    direct view, V-series) which is about 6 or 7 years old. The
    problem(s) appeared suddenly today. Black levels have become much
    more bright (gray), and the colors have taken on a bluish tint. The
    blue tint is not overpowering, but it gives blacks a bluish glow, and
    reds look a bit magenta. Adjusting tint doesn't really help. Whites
    and yellows are less obviously affected by this strange blue effect.
    The grayish blacks combined with the blue tinge gives the picture a
    flat lifeless appearance. Input doesn't matter, DVD/VCR/cable all
    show the same effects.

    I can make the picture look tolerable by greatly reducing the
    brightness, but then I lose a lot of picture detail. Something
    clearly has gone amiss, any ideas or suggestions?
     
  3. I haven't worked on TV's in years, so this is speculation: We used to do a
    thing called tracking, where we went for a perfect black & white picture --
    no color tinting anywhere. For your problem, check for controls marked blue
    screen, blue gain or blue grid and start tweaking. Do it with a B&W
    picture; go into setup and set color to minimum, avoiding confusion caused
    by color in the picture. (The mention of blacks that are now gray gives me a
    problem. There's no one single tracking adjustment that would be "off" to
    cause both that AND the tinting problem.)

    If it changed once without provocation, it may mean something failed that
    you can compensate for with an adjustment. The flip side is something is
    failing that will continue to fail. Time will tell.
     
  4. Art

    Art Guest

    Sounds like either th eCRT is gettin weak or the AKB circuit is having
    problems, most likely the CRT is getting weak and the AKB can no longer
    compensate.
     
  5. Xmttrman

    Xmttrman Guest

    If the picture suddenly goes bad such as described here, component failure, such as small
    electrolytic caps is a good possibility. There are many caps in the CRT screen supply that fail
    producing similar symptoms. I could give you values of caps to check but tearing into a Sony chassis
    such as this is a major undertaking.

    If the picture was clear/in focus/good black-white tracking, etc before this problem occured, I
    would advise repair. If the picture was not.... don't fix it.
    If you do repair it, find a QUALIFIED Sony repair shop. Sony factory service costs $$$ but you will
    get a good repair.

    -rcs
     
  6. Cross-posting corrected.

    Actually, we have pretty good results with restoring Sony tubes with a
    Sencore CR7000. It depends on how they test, but the set is certainly worth
    a check. Be sure to find someone with a good CRT tester who has experience
    using it and can recognize which tubes can be worked with and which ones are
    ready for the scrap heap.

    Leonard
     
  7. Paul Jackman

    Paul Jackman Guest

    Hiya

    Personally I would forget repair, it's never very sucessful on trinitron
    tubes, leave it be, don't fiddle with the adjustments too much cos it
    often just makes it worse.

    Be prepared to buy a new set fairly soon, alhtough it may soldier on for
    years.
     
  8. Interestingly, I just had a Sony KV27EXR25 (1991) come in with the pix
    flashing on/off. Tested the CRT and found emission very low. After
    restoration I get full scale emission and no drop on the life test,
    indicating a very successful restoration. In my experience when they test
    like this the customer has quite a lot of life left in the CRT. The pix
    looks great. Good focus, near perfect gray scale tracking, stable cutoff.

    Charges $89 + tax, including resoldering a few connections that tend to
    cause problems in the set and adusting, leakage testing. Highway robbery
    according to Ken, I am sure, but then I wonder if he has invested $2000 in a
    CRT tester.

    Leonard
     
  9. Art

    Art Guest

    My experience with restoring CRTS have been both good and bad, we always
    told the customer that they had absolutely no warranty on the CRT or it's
    restoration, that it could fail at any time!! Most of the time you can buy
    the consumer a couple more weeks or months of reasonable picture quality in
    doing this but you are just putting off the obvious, they will either need a
    new set or CRT eventually. When the customer agreed to having the
    restoration done we would tell then it was $50 US cost to do it, again with
    no warranty. 90% of the time they would opp for the procedure. Had many
    return calls from these customers when they finally were able to upgrade to
    a new set commenting that they appreciated our candidness and truthful way
    we handled our business. .
     
  10. With experience and a good tester it is possible to get a good idea of when
    a restoration will last a while. If the results do not test very strong we
    don't charge for the restoration at all, just the normal estimate charge,
    even if it improves the pix.

    Similarly, we advise customers that there is no certainty about the life of
    an aging CRT. We offer 90 days warranty on the restoration that can be
    applied to the purchase of a new set if it doesn't last. We tend to be very
    conservative about doing CRT restoration. If the tests are marginal we
    don't recommend it.

    Leonard
     
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