I managed to damage the LCD thermal sensor socket in the logic board. Now the connector won’t stay in place. I know the missing thermal sensor should cause the fans to spin up (they do spin up after a while), but the screen is blank.
I connected an external monitor and it works fine, so it doesn’t seem to be a graphics or logic board issue. I also replaced the LED driver board with one from a working iMac, to no effect.
Can the missing thermal sensor be causing this?