LCD failure; works under some circumstances but not by itself?
Quick summary of my issue:
- Starting from a normal boot, my display works until the login screen. From there, it either freezes and the bottom backlight is flashy, I get a black screen with my mouse stuck in the top left, or it shows my background & password field but gets dark and slowly fades dark purple.
- If I shut and open the lid, the screen either stays how it was (frozen at login) or displays a random barf of colors. It is different every time. Sometimes a solid color, sometimes a pattern. It doesn’t really matter, there’s no GPU in this model.
- If I boot to recovery, diagnostic, or safe mode the internal display works perfectly fine.
- If I boot normally and plug in an external display via HDMI, the internal display works fine UNTIL I unplug the external display at which point the internal display will either freeze or the backlight will dim and the display will slowly fade into a dark purple.
I’ve tested several other displays, and the results are mixed. Some have no backlight, some start with no backlight but then the backlight turns on, some have no backlight or image, and some act exactly the same as the original. These other displays are all broken screens pulled off other 2015 machines that were otherwise working despite cracks in the LCD.
I’ve replaced the backlight and display driver twice on my board with no change.
I’ve tried every combination of turning it on with different things disconnected from the board. And of course I’ve reset the SMC, NVRAM, and tried a reinstall of Mojave and even started from scratch at Yosemite. But of course that did nothing.
Oddly, it works perfectly if I install and boot Windows.