700m laptop backlight fails after 1 min.

Discussion in 'Dell' started by John Vallelunga, Apr 30, 2008.

  1. My wife's 700m laptop backlight will light up when first turned on, but
    then shuts down after 30-200 seconds. An external display works fine.
    I assumed this was an inverter problem and bought a new one. I replaced
    it today, but the problem remains. And yes, all the connectors seem to
    be solid.

    After some research, others have suggested the lid-closure switch could
    be the culprit, but this switch seems to be working just fine. I can
    boot to the bios and see the backlight come on and off as I activate the
    switch (this assumes I do it within the 30-200 seconds that it works.)

    Two questions:
    1. Can a bad backlight tube cause this problem? It seems to work
    fine, and has normal brightness when it works. Could it be taking too
    much current which makes the inverter stop working? Could it require
    more voltage once it warms up? Any chance that replacing the tube will help?

    2. Any other ideas or suggestions?
    Thanks, JV
    John Vallelunga, Apr 30, 2008
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  2. hmmm....Interesting.
    Well a new tube only costs $10 (+ shipping) so it is probably worth the
    gamble. Anyone else fix this the same way?

    John Vallelunga, May 1, 2008
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  3. You might be on to something here.
    I tried a tube from another old display and, although it was not the
    right size, it did remain lit.
    I am going to order one now. Thanks
    John Vallelunga, May 2, 2008
  4. Well, I hope to be able to fix this myself. I ordered the tube already
    and it should be here by Monday. As it happens, I ordered it from
    Moniserv. I am used to taking things apart, and am an EE, so I am
    hopeful. The display I took apart to try the experiment was very
    simple...the tube assembly just slid right out....no skills necessary.
    I will let you know how it goes.

    John Vallelunga, May 3, 2008
  5. Well Sh!t! I got the tube today and I must admit this was a very
    difficult job. I am very used to working with microelectronics (over
    30years), but this had me pretty much beat. The tube on these is very
    difficult to remove. I was hoping for something much easier...like the
    display I took apart to test it. This 700m display is extremely
    difficult and without instructions, I would never attempt it again.

    On the bright side (no pun intended), I did manage to replace the tube
    and it did solve the problem of the light going off after a minute or
    so. So if you have this problem SEND YOUR UNIT IN for a tube
    replacement! The laptop works just fine now except for one minor
    problem that I caused. Somewhere in the process, and I have no idea how,
    I managed to crack the display in a corner. I now have a working
    display except for a big hole in the corner....but the other 95% works.

    Oh well. My wife has already ordered a replacement laptop (she did not
    think I could fix it) and it should be shipped this week. I guess this
    unit will go on ebay AS-IS. It would be a great server and it works
    great with an external monitor.
    What a bummer!
    John Vallelunga, May 3, 2008
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