TV hisses, pops, and went out for good

Hissing and popping generally would point to a PSU problem, specifically:

a capacitor

1 or more diodes

a device on a heat sink

In that order.

I don't see anything to indicate a bad cap. I can't see the devices on the heat sinks, so one of them might contain some charcoal.

Start with checking the fuse.

Then eyeball and smell the board.

Then test the diodes with the diode function on a DVM.

Replace parts as necessary.

I'm betting the fuse and a diode or two.

@blueicefrostyy looks like your power board got hot (very hot) check the area of the red markings. The IC's thermal paste does not seem to healthy either. I would consider that the sizzling culprit. Removing the board and checking it from the bottom side may also shed more light onto this. The very first checks would have been to see if your POwer LED comes on, if you have power on the board at the fuse and if you have the standby voltage as shown on the board to be at 13VDC. Use a multimeter on DC settings and place red probe on the pin as pointed to on the board and black probe on ground. Since this is going to a kive test (plugged in and turned on) there will be power on the board. Do not touch anything with your bare hands. Could be a shocking experience. If you do not have that, you could try and find a schematic for the board or replacing the board.