Chosen Solution
So I attempted an LCD replacement from a mid 2015 BTO integrated graphics card, replacement Lcd was to be installed in my mid 2015 dual graphics card. All the connections were the same nothing was different, except after powering on the display there is no light, although you can see the desktop folders icons and etc. Nothing leads me to believe that the display was defective in any way shape or form as it works in the previous machine MBP. My question is are the displays different for the discrete versus the integrated graphics card? Of course I did all the necessary resets, SMC PRAM!! Ugg Otherwise the machine works perfectly on an external display, It also recognizes the retina display but it won’t allow me to adjust the brightness. Update (12/27/2018) A small drop from 6”… lol Display went dead but everything else works. Update (12/28/2018) So here’s to images I found I’m not sure of the location of this fuse, The zoomed in image is of my logic board, The other is from a thread I found here. Any help is greatly appreciated!!
Hello, Did you replace the LCD panel, or the entire display assembly? You could have gotten a defective part, but it could just as easily be a problem with the backlight output on the board (you can blow the backlight fuse if the laptop is on when the connector is removed / inserted). I would disconnect the battery, remove the LCD cable, check the end for damage, and reinsert it if it looks OK. If you are comfortable with using a multimeter and probing small things you could check for backlight output voltage. I wouldn’t attempt this if you are not comfortable however, as it is relativity easy to slip and short something out with the probe tips.
From the sounds of it you need to replace the backlight fuse on the logic board and you should be OK, I’m assuming the system was running at the time so the backlight logic was shorted out which is why the backlight is still out with the other display. I wouldn’t waste the effort swapping the display around again. The display is more likely OK, its the logic board its self that needs repairs.
