Model A1418 / Late 2012 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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iMac Will Not Turn On

I have a late 2012 iMac 21.5" that will not turn on. Black screen, no gong, nothing...

I've disassembled the iMac and looked at the diagnostic LED's and found that only LED #1 (at least I believe it is #1) is the only one that turns on. I then tested the power coming from the power supply which is giving me 11.79 volts on the following Pinout.

0 - ground

0 - ground

0 - ground

0 - 11.79 vdc

0 - 11.79 vdc

0 - 11.79 vdc

From what I read this is pointing to the logic board but I wanted to make sure from the Pro's out there in this forum. Shouldn't I at least be getting 12 vdc and not under that? I've watched it drop from 11.84 vdc to 11.79. Please see the following pictures to understand what I described above.

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Answer this question I have this problem too

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Did you end up fixing it? i have the same problem with mine

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I see this question is backdated a bit and hasn't been replied to. I dont know if you still need input on this one or if its too late.

LED one indicates that the logic board is receiving a trickle charge from the PSU. when you push the power button, the second LED should come on, indicating that full power has been received, then the 3rd indicates the GPU initialising, and the 4th indicates the LCD is connected and enabled.

if you get no second LED, then i'd initially check that the power button hasn't been damaged.

You can start by unplugging it and shorting out the power pins.

If you still get no response, then it could be PSU or logic board, but its hard to trace without a process of elimination of some kind.

I hope this helps.

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steharmon will be eternally grateful.
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