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A1418 / EMC 2833 / Late 2015 / 3.1 GHz Core i5 or 3.3GHz Core i7 Processor. Released October 13, 2015.

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Need to test power supply from this iMac before buy a part

I got a problem with my iMac 21.5 retina 4k display model A1418 EMC 2833 the computer doesn't come on at all and I need to find a copy of the Apple technician guide iMac 2015 that way I can run a test for a power supply before buying a replacement part, so please someone can give me the PDF of this manual or someone tell me the volts for each pin on this power supply I appreciate so much thanks.

Update (04/30/2018)

Imac 21.5 4K 2015 this is what the led 1 make with the new power supply

Answer this question I have this problem too

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Surprising Apple has on-board diagnostic LED's on their iMac's!

It is the easiest way to see if you need a new power supply or not. Here's the location and def's on what the LED's mean:

Block Image

  • LED1 - Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. 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 source is disconnected or the power supply is faulty.
  • LED2 - 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.
  • LED3 - 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.
  • LED4 - 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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what about if the led 1 just blink for a second and then stay off wen i plug in the power source ? and the power supply make a little tiny noise like capacitors or small relay working


Bad power supply


I just buy another power supply and the motherboard still make the same thing the small led light 1 just blink went I connect the power cord


2017 iMac 21.5. Computer will work for a couple days the die. led1 and 3 are off. Led 2 flashes and led 3 turns off and stays off.

Un plug for a couple days and then repeat.



@Aaronr90 - See if replacing the PRAM battery fixes things. If not your logic board has issues.


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