Chosen Solution
Computer was working fine except for old battery and a broken key on the keyboard. Ordered a new topcase and battery, swapped everything over… The machine will power up but there’s no chime. fans spin, caps lock works. but the display shows nothing and no backlight.
I had a similar thing happen with a repair I just did on a 2015 MacBook Pro Retina. Did the screen replacement just as I did with all others in the past, and in trying to turn it on it had no life. An SMC reset (Hold Shift+Control+Option+Power button) was able to get me fan spin and the keyboard backlight, but no picture. I am not sure if there is some sort of sensor that can make the Mac tell when the screen is open or closed, but when I had just about given up on it I closed it and noticed that the Apple logo on the back was lit. I opened it and saw the display was functioning fine. I’ve noticed that sometimes I have to close it and wait for the backlight to come on before I can use it. After a week or so it started functioning normally. TLDR; Just do an SMC reset and then give it some time to power on, and try opening and closing it until the screen turns on. Not sure if my situation was an isolated incident, but this is what worked for me. I hope this helps!
@j__ - Thats Good! But, still not great ;-{ So that implies we either have a blown fuse on the backlight power line or the backlight logic on the logic board is damaged. Do you have a DVM so we can check the fuse?
