Chosen Solution
I replaced the logic board on my A1342 the other day, and this time everything works, except the internal display. It’s still giving me the black screen with backlight, although if you close it immediately after turning it on, it will show something on the external display. (I’ve tried with the old logic board, still nothing) Is this an issue with the display itself or something else? Edit - I should mention that I didn’t set up the computer when I wrote this, now I have and it functions as a normal MacBook would do when connected to another screen, only of course the main screen is dead.
Nagayoshi765 since everything else seems to be working well it is possible that this is a display issue. Of course make sure that everything is properly connected and that nothing got damaged around the display connector. I am certain that you already shined a flashlight against your screen to ensure it is not a backlight issue.
