It is either the backlight LEDs or the power supply, especially since part of the screen went dark a bit before the pop.
The power supply board is responsible for driving the backlight LEDs.
If you have a very powerful flashlight, try shining it on the screen and seeing if there is still a picture (something with lots of white works well, since darker colors are hard to see without a backlight).
Since you still have sound, that means that the low voltage section of the TV is still functioning.
If you do still have picture, you should try opening the TV and looking for obvious damage on the orange(ish) colored board that should be visible. Please make sure to not touch that board, too. It carries high voltage AC and DC, and will still have power left in the large capacitors on it after it is turned off. Things to look for would be scorch marks, cracked/burned components, and bloated capacitors.
If you see any of those things, the board is definitely bad. If there aren’t any of those, there’s still a chance it’s bad, but it could be the LEDs too.