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1.8GHz dual-core Intel Core i5 (Turbo Boost up to 2.8GHz) with 3MB shared L3 cache

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MBA Mid-2012 Screen doesn't work when dimmed (Backlight Question)

Hi, everybody! I have a Macbook Air 13" Mid-2012 that I've been able to troubleshoot pretty effectively up to this point, but now I need the advice of experts!

After suffering a water spill (I don't know how severe), the laptop display has been intermittent. Sometimes it works, sometimes it doesn't, sometimes it flickers. It works 100% perfectly when attached to an external monitor. If it's not working, sometimes moving it around, applying pressure, etc. might make it work to the point where you get a working display.

So... I took the back off and cleaned everything with 95% isopropyl alcohol and a toothbrush, let it sit long enough until it was dry, and then re-attached the display cable and the battery cable. There was no change in the behavior. Previously had reset PRAM and NVRAM and whatever else I could find online to rule that stuff out. No change.

Since there was no brightness at this point (after turning it back on and plugging into power), I used my flashlight to determine that *yes* there was a display and I could log in and clearly make out the icons, etc. with the use of the flashlight. Without the flashlight, it appeared completely dark, not just dim.

So... I moved the MBA around a bit till I got a dim image, logged into OSX, and then maxed the brightness using the F2 (brightness up) key. The display seemed to work perfectly. Then, I went to both the display settings and power saver settings and completely unchecked any display dimming feature. The laptop seems to work 100% with the backlight maxed out by software. I can reboot, shut down, etc... and it always comes back with a properly working screen. However, if I use the F1 (brightness down) key to dim the screen, when it reaches a halfway point of dimness, the screen flickers badly. **EDIT! On my fourth reboot, after working fine for hours, it did not come up bright, it came up dim again. AND... I confirmed that OSX thinks the screen is still at MAX brightness, and changing brightness does not impact the display at all. So clearly this is not a permanent solution, and OSX thinks it's putting out the right amount of power to light up the screen super bright!!!**

Given all that information, and that this was caused initially by water damage, what is the probable repair solution? Should I be looking to replace the backlight fuse? The driver? Is there a ribbon cable that might be iffy on the Mid-2012 MBA 13"? I have the behavior pretty much nailed down, I just want a permanent solution that isn't hopefully going to break the bank. Any help is welcomed!

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1 Answer

Did you try cleaning the motherboard with Isopropal alcohol? If not go ahed and do that. If you did it is very probable that water got in to the LCD panel and killed the backlight. Those leds are very sensitive to well anything. I have the same symptoms on my late 2008 MacBook pro. A display replacement fixed it.

Heres the link:

MacBook Air 13" Mid 2012 Display Assembly Replacement

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Thanks for the quick response, and yes, I did try cleaning with alcohol. It seems unlikely that the backlight/display is damaged, since it can work at 100% if the conditions are right (brightness maxed, etc.) The backlight can still produce plenty of light, it's just sporadically doing so. If I had to guess, it's something in the fuse or backlight controller, but since I'm not an expert, it's only a guess!

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Is there any bright spots on the lcd? Like brighter then it would normally be? And have you cleaned the actual cable end? That is another thing that could affect it. Personally I think the LCD controller board is what has damage not the motherboard but we might as well try everything before replacing parts.

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