Tv goes black with sound on.

@mark34041 First you need to verify that you have no image on all inputs. Try all of those. If it remains dark, unplug everything that is plugged in the back of your TV. unplug the TV and push the power button for about one minute, then plug it back in. See if that resets your TV.

If it remains dark, turn the TV to a channel where you can hear the sound. Next, use a flashlight and shine the beam at an angle against the screen. See if you can make out shadows or shapes. If you do, then it is your backlight that has failed.

If you do not see anything, unplug your set and remove the back cover. Then visually check the boards for any obvious damage like domed or leaking capacitors. Check all the wiring and unplug the wires and plug them back in, make sure they are properly seated. Post some images of all of your boards with your question. Use this guide iFixitでの質問に画像を追加する方法 for that so we can see what you see. It is possible that this is either a power board issue or a T-con board issue.