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laptop screen backlight off

Discussion in 'Hardware' started by daingu, Sep 20, 2010.

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  1. daingu

    daingu Thread Starter

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    Here's the problem I'm having with my laptop. I turn it on and you see it initially come on with all the text: i.e. Dell logo, drives connected, ram, etc. It then goes blank. I thought something was wrong with the motherboard, but if you wait a bit you can hear Windows start up. If you look closely at the screen you can still see everything: desktop, shortcuts, taskbar, everything. It is almost as if there is no backlight.

    Like every laptop there is a small button of some sort near the hinge of the screen that when pressed turns the screen off for when you close the lid. If I push this down for a second and then release, the screen shows up again like normal, but then it will immediately turn back off (backlight off ,but can still see everything if looking closely).

    I can plug up a secondary monitor and this works fine. When I plug up the monitor I have to hit the 'Fn' key and the 'crt/lcd' button to get it to link. Curiously, the laptop screen flickers on for a second, but then goes black again.

    Anyone with an idea of what is going on? Is it just the switch near the hinge that is the problem? I was thinking maybe it was the switch or spring in the switch getting old and always being in the state of pressed down. Pushing the button and releasing only temporarily springs it up for the screen to come on, but drops back down. I was thinking if it were just this switch, maybe I could just remove it and then screen would work again.

    Comments/suggestions?
     
  2. arknorth

    arknorth

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    Having just replaced the backlight on my Dell D510, I can ask simple pertinent question -

    When the picture went dark, did the image seem a touch red to you just before it went dark? (This can be confirmed if you see this 'red' shift when you're pressing the Fn+F8 keys and the screen flickers or pressing that hinge power button.) This is a sign of a blown out backlight bulb. Replacing it will be fun. Which model Dell is this machine?

    A-N
     
  3. daingu

    daingu Thread Starter

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    No, I didn't see it turn red. It just goes black. I don't remember the exact model off-hand. It was an Inspiron. I get you the model number if that makes a difference. If the bulb is blown, would the screen still be coming up momentarily when I hit fn/F8 or the hinge?
     
  4. arknorth

    arknorth

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    Yes - its a fluorescent bulb (just like the ones in the ceiling) - if you've ever seen a dying one of those, they will flicker. It could also be a bad backlight inverter (the power unit for the light), which hangs below the screen inside the bezel. Either way, it means -

    1 - Removing the screen from the laptop
    2 - Opening the bezel - the screws are hiding behind all those rubber feet
    3 - Removing the LCD from the bezel
    4a - Replacing the inverter
    or
    4b - Untaping and replacing the flourescent backlight (usually two screws and some tape is what keeps them attached to the screen - but its a very delicate job) which usually replaces the inverter as well.

    This can be done at home - but it is one of the most tricky jobs to be done to a laptop, and the most pricey if done by a repair shop - oddly, the bulb and inverter are usually cheap to get, its just the labor that drives the repair costs through the roof!

    A-N
     
  5. daingu

    daingu Thread Starter

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    do you happen to have a picture of the bulb and inverter or know where there is one online so I can see what I'm looking for? also a place were I can purchase these items, since you've done this before. you're help is greatly appreciated. if I can fix this without having to take it in somewhere that would be awesome.
     
  6. arknorth

    arknorth

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    Welll... that's why I need to know exactly which Dell you have - the reason being, they may look alike, but when it comes to screen configurations, they're all different. An example would be (like the one I use), this -

    Inverter - http://k-vlaptops.com/bmz_cache/f/f8f80befdb88de9e049b555c430eedb2.image.300x289.jpg

    The Bulb - http://cgi.ebay.com/New-DELL-LATITU...066?pt=LH_DefaultDomain_0&hash=item2eaee185da

    The assembly - http://www.enext.co.uk/images/products/567_img.jpg (all that along the bottom of the screen)

    A-N
     
  7. lewmur

    lewmur

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    I doubt that the bulb is bad. I've never seen one behave as you've described. It is more likely to be the inverter. You should be able to find one on eBay for under $10.

    Go to the Dell site and get the maintenance manual for how to disassemble the laptop to change the inverter. Unlike changing the bulb, which can be a nightmare, changing the inverter is fairly simple if you have a philips screwdriver that fits the "jeweler's" screw.
     
  8. daingu

    daingu Thread Starter

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    cool. thanks guys! I hope it's the inverter. I'll post the model number once I get it. I've taken this laptop apart a few times already so that shouldn't be a big deal.
     
  9. arknorth

    arknorth

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    Ah - a true owner of a Dell laptop! ;-)

    Good luck!

    A-N
     
  10. daingu

    daingu Thread Starter

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    it's an inspiron 600m
     
  11. arknorth

    arknorth

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    Okay! That would be the Inspiron version of the Latitude D600 series. That would be the same setup as my two Dell laptops (this D510 of mine and the Mrs' D600).

    As for the question of the inverter Vs the bulb - AND general rule #1 when it comes to flourescent lights - (And this is where the computer looneys just had to confuse everyone and call them inverters - in the lighting field this little beastie would be called a starter or a ballast - and YES, technically, this divice in the laptop is BOTH an inverter AND a ballast - the bulb works on an AC current [the laptop provides it DC], which is why the power needs to be inverted, but it also has the chargers of a ballast built into it to turn the bulb ON) - when you replace one, you usually SHOULD replace the other and for this simple reason...

    What kills a ballast/inverter? When a bulb begins to die, it makes the ballast/inverter work harder to start it and keep it running (Ever see a flourescent bulb blinking along with an annoying buzzz-CLICK! sound? That's not the bulb making that sound, that's the ballast). So replacing the bulb and leaving a worn out ballast/inverter shortens the life of both.

    A-N
     
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