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A1418 / EMC 3069 / 2017 / Processeur quadricoeur i5 à 3,0 GHz, quadricoeur i5 à 3,4 GHz ou quadricoeur i7 de 3,6GHz. Sorti le 8 Juin 2017.

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LCD won't come on — LED #4 is low and #5 is off

I upgraded RAM and SSD of a 2017 iMac 21.5”, everything went good.

I was at the last step where you have the adhesive strips ready to be pulled off and you actually plug the LCD connectors to see if everything works before removing the outer part of the adhesive and then sealing it.

Boot was good I could see the factory reset screen, and then.. something bad happened.

The LCD panel slipped by an inch or two and the LCD connector:

Block Image

disconnected by the force of the LCD dropping down… the power connector remained connected and visually there is no damage.

The LCD went dark and now the LEDs are like this:

Block Image

the LED #4 is low and #5 is off.

I have another iMac 2017 same model, so I actually took the monitor on the faulty iMac and it works on the un-damaged iMac.

I think I damaged the LCD connector on the motherboard… not sure of what to do now.. any ideas?

The connector doesn’t look damaged.. but I guess something got unsoldered:

Block Image

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It does look like the connecter is damaged the top edge looks pulled. See if you can take a picture looking down into the connector slot.

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3 solutions

Solution retenue

Ended up going to a repair shop, the connector on the board was damaged. Thanks for the replies!

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I would start with connecting an external display and seeing if you get image that way. If you get display, shut down the computer, then check the LVDS cable where it slides into the socket on the board. If the pins are damaged, you could try replacing the LVDS cable.

Also connect the display and power the computer on. Use a bright light and shine it on the screen to see if you can see a faint image on the screen.

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> then check the LVDS cable where it slides into the socket on the board. If the pins are damaged, you could try replacing the LVDS cable.

the cable is fine, I tried the faulty display and its connector on my other undamaged iMac and the screen worked

> Also connect the display and power the computer on. Use a bright light and shine it on the screen to see if you can see a faint image on the screen.

no faint on screen

I have to find a thunderbolt + adapter + display to try with an external display

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btw thank you for your answer; also, do you know what is LED #4 for?

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@phil_lgr I'm not sure what LED #4 is for off the top off my head. I could try to do some research and find out though.

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@phil_lgr If you are not getting display with an external display, you likely have a logicboard issue (replace the device in most cases, but not always). However, if you get display on the external monitor, you likely need a display replacement, Without having the device in my possession it makes it difficult to diagnose.

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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 dedicated GPU are communicating. This LED will be ON when the computer is communicating properly with the dedicated GPU. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the logic board needs 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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Philippe Léger sera éternellement reconnaissant.
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