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

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Power supply or logic board?

Hi all,

I'm trying to determine if I have a bad power supply, or logic board on my iMac, big difference in the price to fix and if its the logic board, its probably not worth it. My iMac is now out of warranty and suddenly won't power up. I've read through all of the threads I could find and done as much testing as I can to this point. Powering up the iMac results in no power, hard drive doesn't spin, fans don't spin, no noise whatsoever. LED 501 is lit, but none of the others. I've tested for continuity on the power switch and it seems fine, I've tried the reset procedure to no avail, I've also tested voltage off the power supply, but I don't know what to look for and some have power, others don't.

Any help would be greatly appreciated.

Thank you.

Answered! View the answer I have this problem too

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I'd replace the power supply as you don't seem to be getting any power past that. Here's how to do it: iMac Intel 21.5" EMC 2428 Power Supply Replacement

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Thank you for responding, I really appreciate it. I have the current power supply out, do you know of anyway to test it for proper voltage output?

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I have a similar issue (no chime, only LED 501 is lit) except that I hear the disk drive and the optical drive spinning (but fans are off). Does is mean that the power supply is working and that it is the logic board that is dead?

Thanks a lot.

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No. The first LED will light even when bad.

LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.

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 LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

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