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Model A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5 or 3.8 GHz Core i5 or 4.2 GHz Core i7 Kaby Lake Processor (ID iMac18,3) / Retina 5K display. Refer to the older iMac Intel 27" Retina 5K Display (Late 2014 & 2015) guides as the system is very similar.

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Backlight Wont Turn On

I bought a new iMac 27" 5K base model so I could replace all the upgradeable parts.

I was able to follow the guides here to easily do so.

Now when I put everything back together and power the system on, I'm able to hear the fans run and also the display is showing the user account start up screen.

My only concern is that the backlight is not at all turning on. This is a brand new Mac and there is absolutely no damage done during the upgrade. All the connectors and cables seem perfect.

Only that when I pulled open the display from its housing, I accidentally yanked on the power cable and the data cable a bit. But there's no damage or lose connections, everything snaps together snug. Just that the back light isn't working.

Any suggestions?

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Can you take a picture with your cellphone so we can see what the screen looks like. Paste it into your question (edit mode).

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What all did you upgrade?

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Plenty of factors in tampering can cause this issue, and the most frequent are listed below.

remember to disconnect power source before any repair.

1) The Connections to the screen are loose: re-remove the screen, and attach it again. make sure you hear a click with each connector you apply. Should you have access to it, i would also suggest cleaning the connections with 99% isopropyl for a longer lasting device.

2) The Flex Ribbon has been damaged: the stress put onto the flex ribbons can not only have the chance to tear the ribbon, but more commonly, partially sever the circuit attached to the LCD/Digi itself. (this is not a visible damage, and is actually inside the LCD assembly. accidents can still happen. In this case, replacing the screen should fix the issue.

3) Inverter Coil Failure: Though most are attached to screens, some are moduler. A small board that the LCD flex attaches to, which processes the Backlight. replacing this may solve your issue.

4) Backlight control failure: Low quality screens, lack of Antistatic protection, and use of metal tools can cause static discharge which damage the motherboard components. A much more advanced repair, replacing components in this circuit should fix the issue.

5) Missing/damaged components in the related circuit: There are hundreds of components on a board. using the wrong tool in the wrong spot, slipping with the drivers or even a drop, can cause failures on the Screen. Manually scan the board for damaged or missing components in the areas you have worked, and replace as necessary. (A microscope is very helpful attempting this)

6) Motherboard damage: If ALL else fail, you have a perminant failure in the PLB, and need to replace it.

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