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

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Not turning on at all.

I have an iMac EMC-2428 to repair and need some help diagnosing the issue.

Nothing happens when the power button is pressed… the diagnostic LEDs show one only, so I know the logic board is getting power.

If I test the voltage across the power button connection at the logic board it reads 3.5V then 0V when pressed.

Any ideas please?

Answered! View the answer I have this problem too

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It was the logic board causing the issue - replaced and working great.

Thanks for your help anyway.

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No, you do not know the logic board is getting power. All you know is that the power supply is getting power. Replace the power supply. Here's how:

iMac Intel 21.5" EMC 2428 Power Supply Replacement

Here's the part:

iMac Intel 21.5" 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.

iMac Intel 21.5" Power Supply Image

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Okay thanks Mayer, Replacement PSUs are out of stock just now so I'll look around and will update post.

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Apple Part #: 661-5299 or 614-0444

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The part number was actually 614-0445 on this one, but I've ordered a 614-0444 and will report back once it's installed - thanks

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The 614-0445 is a manufacture part number not an Apple part number. Sometimes they are close, not usually this close.

http://www.powerbookmedic.com/parts/661-...

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Did not work - just the same symptoms, 1 diagnostic LED and nothing when the power button is pressed :(

I've also tested the output voltages from both power supplies I now have and they are producing the same - I am also getting the correct voltage from the AC in.

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Paul will be eternally grateful.
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