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Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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No power on iMac

Hey guys,

I have an iMac emc 2428 that is not powering up. The unit was left in sleep mode overnight and the next day it wouldn't power up. When the power button is pressed nothing happens, no noises or fan spin.

I've tried multiple known working power cords and different AC outlets. I've reset SMC and tried leaving it unplugged overnight and tried the next day, still no signs of power.

Apparently there are diagnostic LEDs that I am trying to locate. I removed the RAM and looked through the bottom vents and RAM slots but couldn't see any LEDs.

My guess is the power supply is dead, therefor no LED. Or the issue is I'm not looking in right spot. I have purchased suction cups but haven't opened the iMac until I know it's necessary.

Any help would be greatly appreciated!



Answer this question I have this problem too

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2 Answers

This series is a bit different than the older models, the diagnostic LED's are located about mid point in the logic board and looking at the system standing are also backwards! The most right LED is #1.

Block Image

Diagnostic LED's marked in green and the order from this perspective is: 4-3-2-1 (zoom the image)

Basically, it's setup so if you rest the system on its back and lift the display up using a foam wedge to hold the display you should be able to see the LED's Follow this IFIXIT guide iMac Intel 21.5" EMC 2428 Display Replacement follow the guide to Step 4 and then carefully lift the display up a bit. Are you able to see any lit LED when you power up the system? If not your power supply is gone.

Update (03/30/2017)

LED #1

  • Indicates that the trickle voltage from power supply has been detected by main logic board. This LED will turn ON when you connect the iMac to a working AC power source. The LED will remain ON as long as the computer is ON or asleep.

LED #2

  • Indicates that computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly.

LED #3

  • Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the backup battery (on front of logic board) may need to be reseated, or the video card might be installed incorrectly or needs replacement.

LED #4

  • Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED #4 is ON and there is no image on display, then LCD panel, LED backlight board, or cables between LCD and logic board or backlight board might be installed incorrectly, or need replacement.

LED #1 = Power available

If first LED is not lit:

  • Disconnect the power cord from computer, then reconnect it to reset the LED status.
  • Verify AC power source.
  • Verify known-good power cord is connected.
  • Verify cable connection between AC inlet and power supply.
  • Verify cable connection between power supply and logic board.
  • Verify power supply.

LED #1 + #2 = Power available, and computer is powered on.

If second LED is not lit when power button is pressed:

  • Verify power button cable connection to logic board.
  • Verify power button functionality.
  • Verify cable connection between power supply and logic board.
  • Verify power supply.
  • Verify logic board.

In your case you've proved the issue is not the power button and the system is getting power, so the issue is more likely the logic board.

Update (03/30/2017)

@gamefreak701 - Here's the power supplies header marked in green:

Block Image

And here is the pins voltages you'll need to see:

Block Image

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Oh awesome, thanks for the response! I opened it it up and only LED #1 is lit. Once I push then power button LED1 goes out and the unit remains dead. I have to unplug AC, wait 10 sec then plug back in to get LED back on. It then goes out again once power button is pushed. Any idea what this could mean? Thank you!


Not good ;-{ More likely your logic board is gone.


@danj Why do you think it's the logic board and not the power supply?


Ok, thanks for the help I appreciate it. This is my mothers iMac so I will break the news. I now need to salvage the data from her HDD. Any tips on that? I know if the computer was able to be booted you could boot into the firewire target disk mode.

Thanks again :)

EDIT: Any other testing to confirm if it's power supply or logic board? I'm willing to replace power supply, but only if I know it's going to fix it.


Yes, the power supply could also need replacing. But more often than not I've found the logic board was the more likely.

You'll need to measure the voltages of the connector or the power rails of the logic board to see whats present or not.


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Sounds like it could also be the Power buttons continuity. Maybe the power button is bad and its shutting itself back off when the button is pressed?

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The buttons rarely fail in the iMac's. What does happen is the connectors get pulled off or the wires cut during repair. As I stated in my remark in my update Adam proved the issue was not the button. From Adam's response: "Once I push then power button LED1 goes out and the unit remains dead" The iMac's use a soft button design so the mechanical button triggers the power supply logic to power up. As the button caused the Diag LED to go out that proved the mechanical button was working and the fact the LED went out also proved the switch logic is working.


Right on thanks for that. I haven't seen it very often but I have seen them stop working. Which is why I Asked about that.


Thanks for the suggestion, Daniel. I'll keep that in mind. Sounds like the button is working from that Dan suggested though.


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Adam will be eternally grateful.
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