Why is my screen dark but I have sound

brucetristen  check to see if this is a backlight issue. In a darkened room and the TV turned on and on a channel that is working (audio present) shine a flashlight beam angles against the screen. If you can make out silhouettes/shapes etc. you know that this is a backlight issue. The backlight gets its power from the power board after being told by the mainboard to turn the backlight on. So if the backlight is not working, you need to check the voltages from the power board to the main board and finally on the power board to the LED backlight. If all of those are correct then the issue is most likely a bad backlight array (common on LG) If the voltages are not correct we will need to know what you measurement were. Post some good pictures of all of your boards with your question so that we can see what you see. Use this guide Aggiungere immagini ad una domanda for that