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  1. #1
    iMac 21.5" - Only LED 1 lights up on diagnostics
    I have an iMac 21.5" Late 2012 - A1418 which started to repeatedly shutdown until eventually it wouldn't switch on.

    I initially replaced the Logic board. LED 1 comes on.
    I replaced the Power Supply. LED 1 comes on.
    I replaced the RAM. LED 1 comes on.

    I have gone through so many articles, and I just can't fathom what the cause of this problem is. Cables etc look fine.

    Any suggestions all of you Mac experts?

    Many thanks

  2. #2
    iMac 21.5" -  Only LED 1 lights up on diagnostics
    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
    Have you checked with the trouble shooting hints and answers at They would probably be of more help than most of us would be. Personally, I do not work on iMacs even though I have years of experience as an electronic and computer tech.

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