Backlight acting up on toshiba tv

Okay, I have a Toshiba 5OL1400U tv, and lately it started acting up, the corners of the screen darkening to where it is hard to see the picture. So I look it up, wondering what it could be, and everything points to the backlight, either it is burned out, or something is wrong with the power supply board giving power to the backlight.

I open up the tv, half terrified I’ll ruin something, until finally I can see the “backlight” led strip on one side of my tv. I plug my tv in while still half dissembled, and turn it on. All the led lights turn on for a brief second before everything but the middle of the strip turns off, then even the middle strip dims, until it is half as bright as it started. This happens every time I turn the tv on.

This problem makes me wonder if the power supply board is bad, not the led strip lights, but it gets better, I took my multimeter and tested the pins connecting the led to the power supply, 8 pins total, four cathode, four anode. I tested anywhere from 12-15 volts between any two of them EXCEPT for cathode 4, my multimeter wouldn’t read a voltage from cathode 4 to any other point. Is this important?

My main question is, what the heck is wrong, and what do I need to replace to get my tv fixed?

Thanks ahead of time, here are some pictures to show you kinda what I’m seeing