Chosen Solution
Dear all, I have a mid 2015 MacBook Pro retina and one day it just flicker and goes black. Works on an external display though. So, I ordered a replacement display and replaced it, guess what, it still does work. i asked a few repair shops and they all say it should be the display but nothing else. Are there anything else that I should test out and isolate the problem? thanks in advance.
Your internal display has two services which need to pass from the main logic board to the display: The video signal for the imageThe backlight power to power the backlight Clearly the GPU is able to supply the video signal as you are able to see the image on an external display so that leaves the backlight power as the issue. Both sets of signals pass though a connector on the logic board which can get damaged from moisture. So I would inspect it
Use a soft tooth brush with some 85% or better isopropyl alcohol to clean the solder joints. If both areas look good then the logic board backlight power circuit needs repairs.
