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モデル番号 A1418 / Late 2012 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7プロセッサ

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No power on this 2012 21,5" iMac

Hello, I have a problem with a late 2012 21.5” iMac (A1418) EMC 2544

Mother board 820-3302-A It does not turn on, so I lifted the screen off

There are 4 diagnostic LEDs

Test 1: With power supply cable connected

  • Black
  • Black
  • Black
  • green

Test 2: If I press the button, there are just

  • Black
  • green
  • Black
  • green

Nothing happens on the other

  • no ventilation which turns
  • no beeps nothing

How do these LED corresponds with this model?

Usually: power unit + motherboard + video card + screen

The I find bizarre as it skips the second and there's only 1 and 3 lit.

Thank you for your help, failure arrival alone

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I have same problem but my 1 led is on, trying to remove battery and put it back, replaced UPS and still same , power Botton works, what else can it be done to diagnose problem , I have 3 iMacs acting same way late 2012

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Wow! This question was hiding!

Its a bit late for fandeimac  sadly ;-{ @michael niedzwiadek thanks for finding it!

So here’s the deal! Here’s the breakdown on the LED’s

Block Image

Here's a breakdown of the onboard diagnostic LED's:

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 still have no power on the second LED I replaced power supply and still same , need to perform turn on without battery or need to replace RAM sticks

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@miksuiek75 - The coin battery is just holding your EVRAM settings. It does not have any bearing on the onboard diagnostics LED's

Unless you leave the system unplugged from power for long durations the battery should be fine.

If you altered your RAM then you could have an issue with a bad SO-DIMM

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fandeimac さん、ありがとうございました！
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