iMac does not power ON
I have a Power issue with my mid 2011 iMac.
I've already opened it up. I have experience with repairing electronics, etc. But now i'm stuck. On the logic board ( Main board) :
- Diagnostic LED 1 goes ON, this seems a power-OK led to me, I measure 12v on the supply.
- If I press the power button nothing happens.
- I detached all peripherals, sdcardreader, camera, audio, hdd, speakers, etc. Still nothing.
- I checked the power button, the button and cables are OK.
- I can also measure 12v on the logic board.
- What can keep it from powering on, what does it need?
- Does it need memory in the banks to power on, ( LED #2) ?
- Could it be a faulty CPU or GPU, does it need that to power on?
- Do all the sensors have to be connected?
- Could I detach the video card an test power without it?
The thing is I don't feel like replacing the logic board, its to expensive, I just wondered if there is any information about the "logic" which turns on the power, could I override it, so I can see where the smoke comes from ? :)..
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I know this is a little old post but Guido hit the nail on the head.
The numbered steps in the post below I appreciate, but it still tells nothing about why the board will not run the fans even.
I've replaced the power supply with brand new one as the old one would only work here and there.
Now I have replaced the logic board & power supply (new), and I only get First LED Lit, Just as always.
But now no matter what I try I can't even get power for fans or hard drive . Even swapping back out to old PS, that would power it up but black screen and hard drive spin up noise.
Tried known good working RAM. checked wires from plug input in the back of case to the board and grounded to the PS standoff to tighten it down.
So #2 is not working for me , and if you do not need it to diagnose, why is the logic board not detecting proper power from the brand new PS <or even the half working old one> on new and old Logic boards, to show me the next LED ? #3 which obviously should be on if I get #2 to light.
But the one led was the problem in the first board I took out . Sometimes on a fluke it felt like , when hitting the power button it would power on but do not dare shut it off as you can sit there for hours or minutes stressing the power button. So I bought a New Working Board from ebay hoook it all together and same exact thing except I have not got it to boot at all now. Can anyone tell me When Dry Testing a Mac board What plugs/sensors/ Devices need to be plugged in in order for video signal to be sent to screen? In other words detailed power from button to Screen as I think maybe a sensor or something is prohibiting the boot . All fans turn on and I know everything else works as I had it running a couple times before board swap . TY in advance,