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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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iMac Core i7 3.4 27-Inch (Mid-2011) EMC 2429 Gets No Power

iMac "Core i7" 3.4 27-Inch (Mid-2011) EMC 2429

My iMac "Core i7" 3.4 27-Inch (Mid-2011) is unresponsive. I've opened it up to find only the first diagnostic LED lit. The other three are off.

Before I buy the power supply and replace, I am trying to think this through. Prior to the computer not booting at all, I have on at least three occasions in the past, had trouble getting it to power on. Previously I pulled the power cord, talked sweetly to it, plugged back in, sometimes into a different outlet, and it has eventually come back on. This time it's dead.

My question is this. Is it possible the problem is in the switch itself? The power supply has no visible signs of damage, and considering the previous problems leading up to now, I'm wondering if the switch was going bad. Or is the power supply still more likely?

Edited to add another note:

I also managed to damage the clip on the sync cable to the LCD when removing it. How big a problem is that? Wondering if I can rig it back somehow.


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1 Answer

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Very nice that you talked nicely to it. Most people put a curse on their machine first, which makes it much harder to repair as it has to be exorcised first. Go for the power supply.

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.


vertical sync cable Apple part# 922-9161

Keep in mind this:

iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program

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What do you think about that verical sync cable? It seems I could just buy a replacement for that. I traced it up the back of the LCD and found where it's fairly easy to remove the other end. In the process of tracing it and pulling the tape off, the tape pulled out the ribbon connection too. Now I'm realizing that I don't know exactly how to reconnect the ribbon connector. Is there a trick to that?


Hello mayer, I have a similar problem. The only difference is that upon connecting the AC to the iMac a LED is lighting up once and then a second time and afterwards it goes black again. I cannot see which LED it is, though. So I checked the voltage on the pins of the logic board. Pin 4 is showing 12V constantly. So I suspect the power supply must be okay. But what's with the LED then? Pin 12 is showing 3.8V. This is the power button pin. I am a bit confused that the voltage stays the same even if i plug out the power button cord from the logic board. Pin 11 should show voltage upon pressing the power button, but nothing there. I suspect the logic board but they are too expensive for an 8 year old machine! Maybe it's better to use the HDD in a Mac mini and sell the rest.


@benjamen50 Power supplies can partially fail. I've ha everything work but the hard drive, or optical drive. Your's sounds bad, I'd replace it. If it is working you will get #1 for sure(most of the time, even a failed PSU will light #1). But if it just flashes it's gone. Very seldom does the logic board fail. In order of failure on this model - PSU, Hard drive, GPU.


Thanks I will get one and report.


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