Black screen but LEDs tested good. What do I do now?

I have a 43S431 TCL TV. I took the tv apart and tested all the LEDs, they all worked individually at 6 volts as well as simultaneously. I plugged the tv in to see if a miracle happened and they wanted to start working, well they come on for half a second then shut off. I’m assuming it’s one of the boards now? But which one and how can I test them? The photo I provided is the voltage from the LED strip going to the power board and the volts on the voltage meter is what I get whether the tv is on or off. It only changes for the split second that the LEDs turn on. TIA