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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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diagnostic lights,i get 1st light good 2nd light blinking and fans

IMac 21.5 mid 2011 A1311

So after replacing the imac with a brand new power unit i get on the mother board from the diagnostic lights 1green

than as i power up the 2nd green light flashing and the fans go on and off?

What would be the next step,what can i check more ore does this mean the MB is faulty.

P.S the problem was caused by a stormy night than after the mac did not power on anymore.

thanks in advance



Answered! View the answer I have this problem too

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Hi so i found out thanks to a online guide that i could download to android phone

There is a detailed info/guide about all that can go wrong and how to find out whats wrong on IMac's 2011

very informative and recommendable !

i stumbled on the link 1st of a forum

But the link was dead so i kept looking and found it as mentioned above for a android download,luckily for me i own one.

So the problem i have is a bad MB,but thanks to this guide i could test more options before having to make such a drastic conclusion.

i hope this link can help others..



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Where did the power supply come from? You HAVE to have a know good power supply to proceed.

To observe the LED's you need to apply power to the iMac with the front bezel off. Please ensure you don't touch any part of the iMac or the exposed circuit boards while you have power connected.

Locate the Diagnostic LED's between the RAM slots and the SATA connector.

The LED's are numbered 1-4 from left to right. You may need to move the SATA cable to get a clear view of the LED's.

If you are using this guide for iMac Intel 20" EMC 2210 and 2133 the LED's are located above the SATA connector and not as visible.

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.

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Hi there Mayer thanks for your reply,yes i know where the leds are other wise i couldn't see them question was if the 2nd green light is blinking on and off and the fans go in the same way on and off,what could that mean?

Bad connector cable,faulty MB i just would like to know what else i could check before i decide its the MB?

the power source is from The they sell good stuff it was brand new not used.

been very careful not to touch anything i followed the manual of Ifix it and actually did it a on a few Imacs before with out problems..only this one won't boot and i get the 2nd green led blinking with the fans going on and off as mentioned,the 1st green led is on as soon i put the AC in so the power source seems to be good.

so ya i got this far.




Hellow did you solved this problem?


i have Imac 2015 but i don't hear any sound and only two led light are on..what could be the issue


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