24" iMac-black screen-image visible whem shining a very bright light on it

Discussion in 'iMac' started by Jeroenvw, Jun 16, 2011.

  1. Jeroenvw macrumors newbie

    Jun 16, 2011
    Hello everybody,

    I have an 24" iMac, of which the screen doesnt work.
    But, when I shine a very bright light at the screen, I can see my desktop.
    So the screen is working, only there is no backlight.
    I like to fix this! :)
    Mac is out of warranty, and I have am not that bad with electronics; so its not a problem to take out the screwdriver and the soldering iron :)

    My question is if the inverter is responsible for the backlight? Or is there another component that might be causing this?
    I think the graphics card is fine, because I can see my desktop.
    Also, when I attach an external LCD screen via the display port, it works fine.
    So I think it has to be something in the LCD panel itself, like the inverter.... or the cable to the inverter... or... the inverter cable is connected to the logic board, so theoretically it could be something on the logic board as well.....?

    Can someone please shed some light (haha word-joke... shed light... backlight....... never mind :D) on this issue?

    All the responses are greatly appreciated!
  2. Detrius macrumors 68000

    Sep 10, 2008
    Asheville, NC
    Depends on the backlight method used by the machine. It's pretty rare that we see an iMac with the backlight completely out. Usually, it's either the top half of the screen or the bottom half, and this tends to correspond with the inverter being bad (could still be LCD). On some of the machines, there's a power cable back behind everything that can be a little flaky that provides power to the inverter.

    I've never seen one of the LED-backlit screens with the backlight out, but there's a backlight board for those, and it could still be the LCD.

    Summary: There's no way to know what's failed without actually seeing the machine.
  3. Warbitrary macrumors regular

    Nov 24, 2009
    Montréal, Canada
    It's most probably the inverter. The same problem you're describing happened to my dad's iMac. We got it fixed at a mac repair shop.
  4. Jeroenvw thread starter macrumors newbie

    Jun 16, 2011
    Thanks for the replies!
    My best guess is still also the inverter.

    Thinking out loud:
    There are two cables going to the LCD panel; one is called LVD. if I look at the datasheet of the manufacturer of the flat panel (Philips/LG), then I can see that this is used for data (turning pixels in the screen on and off), not for power. So based on this I conclude (for now) that this is working as it should because the screen displays like it should (only with no backlight). I also think this rules out the graphics card as the cause of the problem.

    Next what I am going to do is remove the LCD panel from the iMac, and measure the inverter cable and it's connections. Maybe I can also find some information on the net on how the inverter gets controlled. There could be a change that the inverter is fine, but it doesnt turn on for some reason.

    I will post my findings here, maybe someone in the future can use the information to fix his/her faulty iMac :)

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