TV Back lights problem

My Philips 43pus6401/12 led 4k TV has a back light problem , they don't work if the back light strips are plugged in to the power board, but will work with a led tester ,the voltage is 26v for 2 rows of 10 led strips and 27.5 for 3 rows 10 led strips all the LEDs are working ,but the power board shows the same voltage output when tested on both red wires , so at this present moment in time I am stuck,