Canadian model number is 58L1350UC. Power supply part number is PK101W0220I.
I had previously repaired this model with a shorted power supply transistor here. On this tv, the backlights would flash on power up which is a sign of bad backlights. I ordered a full set of backlights since the owner said it had been previously repaired and it may have been run at maximum backlight level.
With the TV opened up, I found one out of five strings with multiple led failures. I replaced all the strips anyways. With the new strips installed and the tv plugged in but off, the string with the previous failed leds glowed. When turned on, the backlights did not come on.
Checking the LED controller circuit on the power supply board, it appeared each strip was individually powered and controlled. I checked all the transistors in the circuit and they all appeared good. I suspected the bad LEDs damaged the LED controller IC OZ9908BGN. I was able to find a replacement on Aliexpress.
Once the part came in, I did have a lot of issues soldering the IC since the part was probably old and there was poor solderability on the pins. With each pin tested for continuity, I finally got the TV to power up with all the backlights staying on.