Vizio E55-e2 ALL backlight goes out after approx 5 -10 min

I have replaced the PS board and checked voltage on PS board and it all checks out. I even tested the with volt meter on the old PS board and it tested out. I tested with volt meter after i purchased the PS board thinking it was PS issue.

Now i am looking at replacing the mainboard where the backlight power is coming off the main board where it appears two cables coming off the mainboard to the LED backlight strips.

When i power on TV the back lights are working and picture shows fine. The two connections going out to the backlights(circled in black) i put a volt meter on the right side it varies from 0 -2 V and on the left side it reads also varies from 0 - 2 volts. these readings are before the ALL the backlights turn off.

After about 5-10min the backlights go out and I put volt meter on those two connections going out to the backlights and the one on the right reads 4.6 V across all 6 connections. The connector on the left reads 4.9 , 4.9,5.0,5.0.5.0,6.4 V going from right to left of the pins

Should i just replace the mainboard?