Chosen Solution
Hi, guys! I’ve problem with my iMac. LCD Display shows black screen (no picture at all), external display works correctly through Mini Display Port - HDMI. 4th LED doesn’t lit up, only 3 LEDs are lit up. I’ve already changed LVDS cable and LCD Display - problem still exists. But if problem is a logic board or graphics - how external display works?
I got the answer for my problem: Blown fuse on the logic board.
See if a flashlight at a sharp angle resting on the display allows you to see the faint image of your desktop icons if it does then your backlight circuitry is the issue. Update (08/17/2017) In that case you either have a damaged connector on the display or the logic board or the cable is defective. Otherwise the display it’s self is bad. Take some detailed images of the connectors on both the display, logic board and cable ends so we can see the pins and the latches. Maybe we can spy what’s up here
