Released June 2012, Model A1278. Intel processor with Turbo Boost, Up to 512 MB DDR5 Video RAM

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Why is my screen having no brigtness?

I opened my laptop after a day of resting and it seemed like it did not turn on, battery died, etc.

So I rebooted with no success.

After reading couple of foras I realized that the screen is still showing all contents. When I hold a flashlight close to the screen, I can see everything, when I point it at the Apple logo at the back I see a normal screen, including colors and all, e.g. a screensaver.

I rebooted, rebooted.. I rebooted the CMD OPTION P R, rebooted the smc, tried adjusting the power saving setting, went through all I found and finally resorted to a clean install and downgrade to Mavericks 10.9.5 {before Yosemite}.

What do I do next?

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Martin, the fuse is a 3A 32V in a 603 package and the driver is a LP8550.

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To check the fuse, all you will have to do is use a multimeter and check it either for continuity, (you do not have to remove it for that.) or check for positive voltage on either end. Use the positive probe on either end of the fuse and the negative probe to ground.

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Hey old turkey, thanks a lot for your help! Just to be 100% sure, the part in my laptop as the one in the picture, is brownish. This one is green . Is it the correct one? Also this is the WLED driver I want to order


Martin, the fuse looks right. Coloring may be a manufacturers issues, not a value issue. The WLED driver appears to be right as well. Google does not translate that page very well and I can not see if there is a datasheet. You could get the datasheet from here and see if you need to find more information. Right now, both parts look appropriate.


I just noticed that one of the LED battery indicators on the left side of the laptop (the 3rd one from right) is constantly on. Otherwise, everything seems to be working just fine. What can be the reason?


I checked the fuse with multimeter today. At 2MΩ setting it reads 0.000, at 2kΩ setting it reads +/- 1. Now I don't know what this means.


The reading of the value does not matter, what matters is that you have continuity by touching both ends. Sounds like your fuse does show continuity.


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Sounds like you're facing a backlight issue here.

Did you sit your laptop down on a wet surface? Some times water will seep in.

Are you up to fixing your own system?

You'll need to pop off the bottom cover to do an inspection to see if the WLED chip is damaged which is the backlight driver. These SMT components do need special tools and skills to replace.

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I left my laptop in a suitcase at a hostel reception on Monday. It was in a pouch in a front pocket of a suitcase, no idea what happened.

Can you navigate me to the WLED chip? The bottom cover is off, I unmounted the cable which leads from motherboard to monitor and inspected it, it looks ok.

To fixing the system by myself, I want to detect the problem, order the part and find somebody who can do it. I watched few youtube videos and that's too much for me.

The computer Model No is A1278, last four digits in Serial No DTY3, EMC 2554.

I found this video guide (, it shows exactly my computer and fixes the fuse for backlight. Mine has also letter P on it.

Am I thinking correctly - is this the WLED chip - the fuse?

If so, where do I get it?

Thanks a lot for your help!


Ok, I get it, the problem should be either the fuse or the WLED chip/driver. Correct? How do I make sure which one it is? Where do I order any of them?

Thank you again for your help!!!


Heres the specs on the fuse: 2AMP-32V in a 0402 package. Here's one source: MacBook & MacBook Pro *No Backlight Fix* (replacement fuse).


But before you replace the fuse make sure the is bad. It's also possible the LVDS cable is damaged as the fuse burnt for a reason. And lastly, the WLED driver blew the fuse.


What are the WLED specs? Little dummy, but how do I make sure that the fuse is faulty? And lastly, I am in China currently, can you check if this is the correct part: ?


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Martin will be eternally grateful.
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