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Why is my backlight only working at a certain brightness?

I have a handed down Macbook Air Early 2014(A1466) that is showing some odd backlight problems.

Upon opening it up the first time the screen was dark, but I could still make out the screen contents with a flashlight. Some searches results yielded that this is a backlight issue. Shortly after that initial bootup I tried booting into recovery mode and the backlight started to flicker until it was fully illuminated, however after a restart the backlight was off again. I did a PRAM and SMC reset, which also did not help.

This initially led me to think that its possibly a bad screen cable causing the problem – I had ordered the proper screw set to open back lid as they aren’t available to buy at retailers in the area. In the meantime, I decided to do a ‘factory reset’ and reinstall the OS (doing all this through external monitor as that still worked).

It’s during this were it gets confusing for me – because during the actual install phase the backlight just simply turned itself back on, clear as day. Even when the screen went dark during the installation a few clicks would turn it back on. However, a restart simply made the backlight go off again, but this time I waited till it fully booted (with external still connected) and checked the display setting – turned off the automatic brightness and as I was switching between the External’s settings to the built-in, the backlight turned itself back on again!

Anyway, I was able to replicate this switching on of the backlight by tinkering with the display settings again, since restarting still did not help. This is also when I noticed that once I got the backlight to work (which would ony be on a low brightness setting) and I attempted to move it past approx. 70% of maximum brightness – it would cut the backlight out, so it won’t turn on during boot up and will not go past a certain point of brightness when I can get it to work.

What could be causing this?



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It sounds like a backlight circuit fault on the board. Something there is stopping it from providing the required power.

A few things I would check are the screen connector on the board, the connector on the cable side too for any signs of damage.

Then the components right near the screen connector then the backlight driver chip (which is on the other side of the board) and components around it for any kind of liquid damage or corrosion. This’ll look like white, black or green crust / smudge marks.

Here is guide for removing board:

MacBook Air 13" Early 2014 Logic Board Replacement

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Thanks - will be inspecting the above mentioned when I get the screwdriver set. Additional question: since the backlight can still illuminate, would it be correct to rule out the fuse as a possible cause?

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Yep correct. The fuse is still working fine as the backlight is still functional at the very least. Location of Backlight driver chip LP8550 is shown here:

https://ae01.alicdn.com/kf/HTB1etqrkr9YB...

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