Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor

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iMac 27" power problems

I am having powe issues with my iMac. I get nothing when I hit the power button. I have installed two different power supplies thinking maybe the first one was DOA, but not the case. There are also no LED lights lit on the logic board when I have it plugged in. I thought for sure it was a PS issue but I was wrong. Any help is appreciated. I have had this computer a little over a year and didn't purchase Apple Care.

Also, prior to this all happening I was hearing buzzing noises out of the back of the screen. I have read that this is a known issue.

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Did you get hit by lightning or have some power line issues just before you noted your system won't work? Do you have it plugged into a surge protector or UPS? Can you tell us more on what happened just when your system died?

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No lightening and no power issues. Yes I have it plugged into a surge protector. Before the system was completely unresponsive I was noticing a buzzing sound coming out of the rear of the computer. Buzzing would change volume when I changed the brightness of the display, so I assumed I was starting to have a power supply issue. The buzzing issue happened for maybe 3 or 4 weeks and than one day when I went to restart my computer for an update, it failed to start back up again. No response what so ever when I toggle the power button.

Again, I have installed two different (new) power supplies and still no luck.

Thanks again!

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Just so we're clear here, review this TN: http://support.apple.com/kb/HT2674. None of these conditions apply correct? Fully dead not a bit of life. If thats so, lets start with the basics: Have you tried replacing the line cord and make sure the surge protector outlet is alive (plug in a light or something into the outlet). Sometimes the simplest problem is over looked.

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Correct, none of those conditions apply. Computer is fully dead. I have tried multiple outlets, and yes, I have also plugged in lamps to verify outlets are working. I have also tried different power cords, still nothing.

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You'll need to trace out with an Ohm meter from the case power socket to the power supply the cable harness and connectors.

I've never seen a cold dead system that didn't have either a bad power supply or a basic AC or DC power harness defect. Don't forget to check the power on button cable connection.

Again, are you sure you have a working power supply?

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How can I test my power supply with an Ohm meter? I am assuming its working, I wouldn't think that this company would send me two DOA power supplies.

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Ok I put an Ohm meter to the back of the power supply and I'm showing a full 120v through it, so I'm assuming its good? I also put it against the logic board and am getting no voltage. Bad logic board? Or should I even see a voltage reading through it when the computer is off?

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I was expecting you to check continuity with the Ohm meter Vs voltage (just safer). Good to hear the AC side works. You'll need to hit the power button and watch what happens on the logic bd.

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Nothing on the logic board still.....

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Starting to sound like the power button has a problem, have you checked continuity across it yet when you press it?

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It sounds silly but is it plugged into a outlet that is controlled by a light switch. If so, make sure the switch is on or plug it in another outlet. If it is plugged into a power strip , make sure it is on. I have had this exact silly thing happen to me. Good luck.

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Not so silly ;-}

Sometimes we get over focused looking for a complex problem, when it's in fact only a simple issue!

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