Dead iMac and out of ideas- full details in post

This is a discussion on Dead iMac and out of ideas- full details in post within the iMac forums, part of the Mac Forum category; Hello, new user here and hoping I could get some suggestions on a really tough hardware problem. Here are the details. Machine: Apple iMac 21.5-Inch ...

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    Unhappy Dead iMac and out of ideas- full details in post

    Hello, new user here and hoping I could get some suggestions on a really tough hardware problem. Here are the details.

    Machine: Apple iMac 21.5-Inch "Core i5" 2.7 (Late 2013) ME086LL/A - iMac14,1 - A1418 - 2638

    Synopsis: iMac will not power on after completing several upgrades / part replacements

    Original symptoms prompting the upgrade

    • iMac works OK, but runs slowly and occasionally “dies”.
    • This is an intermittent power / wake problem
    • After going to sleep, iMac would be unable to power on.
    • No combination of power button / keys would wake or boot iMac
    • Only temporary solution: to leave unplugged for an amount of time and try again


    Initial repair/upgrade attempt



    (few photos of the process here)

    Put everything back together and hit the power button. Nothing.
    Machine will not power back on after repairs/replacements.
    It booted once, randomly (?!) after indeterminate changes.
    I manually shut computer down (*regret doing this*), never started again.

    Diagnosis / Troubleshooting attempts


    • Replaced HDD with SSD→ Reverted this, old HDD back in
    • Repaced 2x4GB RAM w/ 2x8GB RAM→ Reverted this, old RAM back in
    • Replaced PSU with new PSU→ Attempted revert, no change, new PSU back in
    • Replaced BR2023 mobo Battery w/ new CR2023 (might as well try?)
    • Reseated all the above components, plug/unplug, re-seat RAM etc
    • Many, many, many combinations of the above


    Description of current state


    • iMac will not power on nor boot, nor make the boot chime noise
    • Screen stays black, does not light up. No beeps. Sometimes I can hear a very faint click sound when pressing the power button.
    • Startup key combinations seem to have no effect (difficult to know w/ wireless keyboard though- I’ve tried a mini USB PC keyboard w/ no noticeable effect). This means all the Reset NVRAM/PRAM/SMC processes seem not possible.
    • I can force the iMac into a “Fans on High” state by holding power button down while plugging in the IEC cable
    • The above implies that the PSU is not dead and the fans at least can power on
    • But no other signs of life from the machine whatsoever


    I have been working off a mental list of 'things I haven’t tried yet' and going through them one at a time. I’m afraid I am at the end of that list. The only things I can think of

    • The motherboard (logic board) is “fried” or dead somehow, I’ve never seen this actually happen to a computer but maybe it does actually happen ?
    • I somehow broke something (?) while doing the repairs, I don’t know what it would be, I’ve visually inspected every connecting ribbon cable and component and seen no damage, I experienced no static discharges at any time, I’ve done this before on PCs and Linux computers many times … also annoying that current state is not *that* different from original intermittent issue state
    • Some unknown Apple-specific angle that I am unaware of as this is my first time working on an Apple computer. e.g. "you'd never know this unless someone told you but an iMac won't boot unless ___ (tiny thing easily missed)"


    I’m at the point where I think I just have to bring it into a computer repair service, as I think this may be beyond me. Frustrating situation.

    If there is anything else I can try here I would love to know, thanks in advance

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