MacBook backlight turns off when brightness is set at 100%
I was using my MacBook today when suddenly the backlight turned off, right while I was in the middle of using it. I know it was the backlight because:
- I have an external display, which remained on, and I could still see my desktop (so the computer hadn't turned off)
- The windows that were on the internal display didn't move over to the external display, meaning that the internal display itself was still on, but just not illuminated
After some experimentation, I discovered that I could get the backlight to turn back on by holding down F1 (to lower the brightness) until the brightness setting reached 0, then holding F2 (to raise the brightness) until it was back at 100%. It was as if the system didn't "know" that the backlight was off until I manually lowered the brightness to 0, and then it would know to turn it back on when I raised the brightness.
However, after doing this, the backlight would only last for a few seconds at 100% and then it would turn off again.
Finally, I tried raising the brightness slowly from 0, and was able to work my way back up to 100% without it turning off. It's been working since.
Is this a hardware failure or a software glitch? I'm running OS X Mountain Lion (10.8.4) and the issue persisted through a reboot.
The issue is caused by a burnt out soldering attaching a cable to an iron bar component situated in the lowest part of the screen. It is part of the module named 612-0035-a. It is the LCD inverter. It is not user solderable with standard equipment.
There's no need to buy an entire screen to fix this, just a new LCD inverter. To prevent same damage from happening again, it is recommended to brace from power surges.
I was able to resolve the similar problem by resetting the PRAM on my MacBook. I followed the helpful article on The Next Web, which along with explaining the how, when & why of resetting PRAM and SMC also contains the instructions:
Shut down your machine. Yes, all the way down, not sleep or logging out.
Press the power button and then press command-option-p-r. You have to make sure you get those keys pressed before the gray screen comes up or it won’t work.
Hold those keys down until your Mac reboots again and you here the startup chime.
Let go of the keys and let your Mac reboot normally.