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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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iMac display not powering up after logic board change.

I recently replaced my logic board, power supply, case and installed an ssd drive. After putting everything back together, the display will not power on. I reset the pram and smc but still no luck.

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What does the onboard diagnostic LED’s telling you?

  • 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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3 Comments:

Thank you for your response. Sadly it was the video card. I baked it and got it going again thankfully! I was worried it was the display.

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What would you recommend checking if led 4 is not lit. I’ve

already checked all connections to the screen.

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@JAFFEE JAY - Your GPU has died

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Francisco C. Hernandez will be eternally grateful.
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