Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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Mac doesn't start after installing SSD

I followed the guide to install an additional SSD in my iMac (27'', mid 2011). After I put everything back in place, it won't start. When I press the power button, the fans start to spin for a short time, then stop, then start again, and so on.

Is there any indicator to figure out what's wrong? I checked all connectors I disconnected when disassembling, they're all back in place.

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I have the same problem. Did you figure out what was wrong? Please help me..


I'm having the same issue. How did you solve your problem?


@fixitm - What do the diagnostic LED's tell you? Review Djh145 for more information on them.


i only have led 1 , but when i press the power button, led 1 turns off.


Lets try again,

The LED's we are talking about are the ones inside the system (Diagnostic LED's). Is that the LED you are talking about here LED #1 ?


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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,

If you take off the display panel and plug the power supply in (taking care to avoid the power unit) you should see a single green LED just off-centered on the logic board. Press the power button and check which other LEDS light up and turn off.

The order for the LED's:


| | | |

LED 1 is lit up then the Logic Board is receiving power and should be on whenever the power supply is plugged in.

LED 2 will light up when the computer is turned on

LED 3 shows the Logic Board and Video Card are communicating correctly

LED 4 indicates the Logic Board and Display panel are communicating. In this case this will not light up as your Display panel is unplugged.

You should try unplug the SSD and see if the machine powers on

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The issue you describe sounds like a P.O.S.T. failure. When you first start a computer whether it's a smartphone or a super computer and everything in between runs a Power On Self Test. This is the first program that every computer runs before the operating system is loaded. If there is a failure the computer will not boot. The P.O.S.T. is controlled by the BIOS. Chance are your BIOS cant' see the drive. The easy way to resolve this issue is to boot into your BIOS set-up utility and change your boot order manually. Chances are with a hard drive change the BIOS can't find the operating system. Also you may need to update your BIOS to the latest version. An updated BIOS may include the driver necessary for the BIOS to read or see your new drive. I had the exact same problem with my Lenovo Y700-17ISK. This model has 2 internal hard drives. When I removed the rotational hard drive and installed a Crucial SSD and reinstalled the OS the computer would not boot. Once I manually change the boot order the computer started normally. Also to boot from a M2.NVME hard drive you must have a dedicated boot partition. I currently run Xubuntu 16.04 64-bit LTS so the procedure was simple. Since you are using a Intel processor your Mac is really a PC. Do yourself a big favor, update your BIOS, install Linux ; there are 300 different versions and you are sure to find something that will suit your needs. This is a very secure, sophisticated OS that will run on any hardware. And the best thing is it's free!

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