Chosen Solution
So after I upgraded my late 2015 iMac 27" and put it back together, the backlight did not turn on when started up. Its just the backlight because I can see everything on the screen if I shine a strong light on it. I recently looked at the diagnostic LEDs on the logic board and the 4th one will not light when starting up. That leads me to indicate the issue is with the backlight board. Any thoughts on how i can fix that? Or, could it be an issue on the display side like the connections? The connections were good from what I could see. I can’t seem to find any info in 2015 iMacs.
The only thing I can think of is you blew the backlight LED voltage regulator on the main logic board somehow. At this point I think you’ll need to throw in the white flag and bring your system into an Apple Store or Apple authorized service center. Hopefully you can weasel your self into a free repair otherwise it could be expensive!
Hello! So a few years later- I also have a 2015 that has no backlight. I went through replacing the logic board, power supply and LVDS and had the same results: 3 leds on and the 4th is off. The only thing I haven’t tried is another LCD. Thoughts? Thanks for any help!
