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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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iMac 2011 won't start up

I need your help/advise,

I've got a problem, couple of months ago I've installed SSD to my 21.5 iMac mid 2011, everything smooth, no issues. Installed Windows in partition and played some games on it (like Diablo 3). For a few times I've experienced that system stuck, and reboot by it self (in Windows), after that it will restart right away as normal. But today with the same thing, and I can't turn it on. After pressing the "on" button, I can hear cooler/HDD/DVD sounds, but there is no start up chime and no response from screen (just a blank screen). Yes, I've left HDD and super drive with SSD.

Most of the posts online suggest to reinstall RAM (I have 16Gb, but it installed over a year ago, no issues), I've tried it, same thing (even with one module at a time). Other common comment to hold Shift+Option+Command+something, to reset something. I have bluetooth keyboard, which obviously is not responding, I got another wired one, same thing. However, my wired mouse blinked when I'm trying to turn on the system. I guess USB port is alive (as well as mother board, I hope).

I've tried to connect external monitor to see if there is some error and my LCD died, but nothing... SMC and PRAM not working either. I've opened the machine to check Power Supply, and LED's indicators. Power Supply showing me 12V at some pins, but the LED test from here (diagnostic lights,i get 1st light good 2nd light blinking and fans), showing just a two lights, in other words something wrong with GPU, I got it right?

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FYI, I've brought my unit to repair centre, and they replaced motherboard (MB) and it turned on, but the screen is flickering now. They suspect power supply (PS) problem, which may burn the MB. Right now waiting for new PS unit, hope it will solve the problem.

PS On the day of burning, my neighbour apartment was under renovation, and they used some heavy equipment, which I think may cause power surge, unfortunately my power filter was temporarily disconnected... ;( So far replacement will cost me ~400 CAD.


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Sounds like a power supply issue. Take a look at the diagnostic LEDS to the right of the RAM slots after removing the frame, and tell us what you are getting.

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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I got 2 green lights from 4 LED's...


And mine doesn't have a frame to remove, just a glass...


I have only the LED 1. Is there a print out for the voltage on a iMac mid 2011 A1312 ECM 2429? Thank you


kika - replace your power supply


That is with the new power supply in it.


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Replace the PRAM battery on the motherboard.

Here's how:

iMac Intel 21.5" EMC 2428 PRAM Battery Replacement

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