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Dell Laptop LCD Repair--Part way there?

Discussion in 'Electronic Repair' started by Iain E. Davis, Jun 11, 2005.

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  1. I've been working on a Dell Inspiron 8100. The LCD was remaining
    dark, after bootup, but I could get a clear picture on an external
    CRT.

    I determined the problem was mostly likely to be the CCFL tube, so I
    ordered a replacement from JKL. The tube replacement went without a
    hitch, and now the display lights up when booting.

    However...the display is still unusable. I can see that output from
    the video card is reaching the display, because as the computer
    software boots, I can see the display change, for example when its at
    the "windows xp loading screen" I can see vertical lines running the
    full height of the screen approximately in the right place
    (horizontally) for the progress meter that XP displays at that stage.

    I checked to make sure the flex/ribbon cable had firm connections with
    the LCD and the video card...without any appreciable improvement.

    My working theory is that I need to replace the ribbon cable, that it
    has developed a flaw.

    Does the inverter simply serve the same role as a the ballast in a
    traditional office or shop light? Or does it play other roles in the
    LCD operation?

    Iain
     
  2. The inverter only powers the cfl tube. The LCD should function without it,
    well it wouldn't light up but you could see something in the right light.
    When people make LCD projectors out of these things you usually remove the
    inverter board.

    - Mike
     
  3. Guest

    The inverter does not serve exactly the same role as a ballast in a
    shop light.
    Most laptop displays have 2 back light lamps, does yours have one ore
    two and did both get replaced if it has two (top and bottom)???

    The inverter generates the start up for the lamps and then monitors
    that there is not problem. If it detects any problem all the inverters
    shut down. Typically there is an inverter for each lamp controlled by
    one ic. Each inverter output has its own surface mount fuse and if one
    lamp went bad, the fuse may have opened up. If one of the inverters
    does not come up, you will get a single flash on power up or screen
    resolution change, then blank. Very common symptom, especially if all
    of the lamps were not replaced at the same time.

    In the units with a single lamp and inverter, it is common for the
    capacitors on the inverter board to go bad and cause same symptom.
     
  4. There is only one CCFL in the LCD. Which I replaced. The new CCFL
    lights the screen and stays lit. It also appears to respond correctly
    to contrast/brightness controls (which are on the laptop keyboard).
    However, my current issue is that what is displayed is significantly
    distorted, to the point that if I didn't know what was normally
    displayed at those points, I'd have no idea what was going on. I can
    clearly see the typical 'flicker' that changing video modes causes,
    etc.

    My question about the inverter was to eliminate it as the cause of the
    distortion, which your explanation indicates to me that I can do: If
    the CCFL is lighting display and staying lit, I can assume that the
    inverter is operating properly.

    Which by my estimation leaves me 2 or 3 points of failure:

    1) The ribbon/flex cable (which dell calls a video harness) has a
    problem between the video card and the LCD...I couldn't see any
    _visible_ signs of damage to the cable, but doesn't mean anything.
    Replacement cost is going to be around $53.

    2) The LCD itself is damaged in some fashion that I wasn't able to
    see, which means I'd need to order a completely new LCD module
    ($503!).

    3) The video card is damaged in some fashion (I currently regard this
    as the least likely explanation).


    Thank you for your explanation, it helped clarify my understanding of
    the role the inverter. I was feeling rather tentative about what I
    knew. :)

    Now if I could only conclusively identify where my "new" point of
    failure is before I go order a $500 (or even the $50) part...

    Iain
     
  5. Guest

    I had an intermittent similar problem with my IBM laptop. Turned out
    the surface mount connector on the motherboard with video had poor
    solder connections. This connector fed the video to the lcd display
    though the mylar cable. If you can run the thing with the case all
    apart, very carefully prod and push on the cable and connector.

    Also do not forget if the cable had an insulator on one side of it
    where the bend is located, to make sure you did not lose it. One side
    of those cables sometimes is not insulated and they put an insulator to
    keep it from touching the grounded/conductive case.
     
  6. Hmm. It hadn't occurred to me that those pieces of tape served any
    particular purpose. However, I made an effort to put everything back
    exactly where I found it when I took it apart, and I'm pretty certain
    I put them back in place.

    As you suggested, I took it apart far enough that I could access the
    cable while the machine was running and gently shifted the cable at
    various points along its path. At no point did the display change in
    any way.

    Just for fun, I took a digital picture of what's going on and put it
    on my personal website:

    http://www.kemenel.org/462.jpg

    This has certainly turned into more of a project than I anticipated!

    Iain.
     
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