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  1. #1
    iMac Late 2012 27" - No Backlight

    I have an iMac late 2012 27Ē that has no backlight.

    The diagnostic LEDs 1, 2 & 4 are on, but 3 is not.
    I can see the graphics on the screen when I shine a flashlight on it.
    It works with an external monitor.

    A while ago I replaced the hard drive with an ssd and all was fine until the screen fell off a few weeks later due to poor quality tape supplied with upgrade kit.

    I replaced the screen and all was fine for a year except occasionally the screen would dim slightly for a second and then go back to normal. It gradually got more frequent until one day there was a green line down the screen and then the next day there was no backlight at all.

    Iíd consider buying a new screen if I was sure it would fix the problem, but Iím not sure if itís the screen or the logic board that needs replacing. Does anyone have any experience with these symptoms? I stupidly got rid of the old broken screen, otherwise I could have just used that one for testing. Itís a bit of a pain using it with an external monitor as you canít see whatís going on at startup - and I occasionally need to boot into Windows.

    Thanks in advance.

  2. #2
    iMac Late 2012 27" - No Backlight
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Keller, Texas
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 7+, iPhone 8, Numerous iPods, Mojave
    Rep Power
    Welcome to our forums.

    You're not the first person that reported their screen fell off due to poor tape provided with the take apart kit. It seems only Apple has the proper tape although it has been reported that other suppliers are now including better tape with their kit.

    A google search yields many similar problems with the backlight on the 27" iMac models. You need to do some reviewing of what those say and advise. Replacing the screen or logic board can be expensive and since Apple has declared the 2012 iMac as obsolete, you're not going to get any help from them.

    My personal advice is not to spend any more $$ on that machine and if possible, sell it for parts and purchase something newer. Or, live with it as is until you can afford something newer.

  3. #3
    Thanks for the response.

    Yes, really annoyed about the crappy tape I was supplied. The machine would have been fine now if it wasn't for that.

    I agree it's probably not worth spending money on it. However it's still a fairly decent machine - top spec i7 and 2gb graphics.

    Most of the backlight problems I have found on google apply to the previous model - which seemed a lot easier to fix. There's not a lot I could find relating to the late 2012 backlight.

    Does anyone know what LED 3 off means - does that mean the problem is with the logic board?

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