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LCD BACKLIGHT and no F1/F2 response

I recently bought a second hand MacBook Pro 15" mid 2012. I thought I could upgrade to 2 SSDs. Upon checking the F1/f2 brightness o roll were not responding. I could see the indicator on the screen where it'll show the brightness going up and down but actually the LCD doesn't becomes brighter or dimmer.

The seller said its due to a software bug. The system was at El Captain. It was stupid of me to believe him.

I bought it and updated to high sierra thinking it would fix the problem But no.

Second problem I found out was that once the system goes to sleep, the backlight won't come back on until I open up the back cover and unplug and replug the battery again.

I went to the Apple Store to get it check and they found a unauthorized modification made to the logic board. Here's are the images. You can see a copper wire connected to 2 fuse I suppose

Block Image

Block Image

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Sorry to say, but looks like you've been had...

So, what going on here is- some reason, your LCD Backlight driver (little square chip above the bottom of the wire) was not receiving its correct signal from the GMUX (larger chip a little below with the silicone stuff around it) If I'm correct, that GMUX would send the signal strength to where the bottom component (resistor) your cable is attached to. That works in tune with your f1/f2 keys and tells the LCD Backlight driver how much to let through.

What they did was connect it to a component that should have 3.3V when the screen is open (basically slamming down the gas pedal for backlight brightness) BUT that signal is also dependent on the GMUX... so it seems like your GMUX is having issues an they made a bandaid fix.

Sorry about the trickery someone pulled on you and how you had to find out about it... That upsets me because it causes doubt for reputable repair shops alike...

Best of luck! If you want it fixed, there are some local repair shops out there that can do it!

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Is there anyway I could order the tiny parts and fix it myself? I've got basic soldering knowledge.

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There are places. To work on this one you would need a Hot Air station, reballing stencil, solder paste or balls, flux, and probably the best bet is a doaner board to take the parts from. They can be found on ebay or aliexpress (a dead board for parts) but... you never know if the part you want is the dead part or not. I would say you should also do some probing around and figure out why the signals are not making it to the LCD Backlight driver, it might be a completely different problem or a missing voltage/cracked trace or something - so some more troubleshooting should be preformed before blindly replacing/reflowing the GMUX. I am not sure if basic soldering skills would cut it, but if you do get a doaner board, practice on it first with taking things off and putting them back on to get the hang of it, then when you feel you can do a bga chip, try it out.

The only caution is, you could easily turn your working macbook with no brightnes control into a dead macbook... so that is the risk.

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