Samsung trouble shooting
symptom no back light
test 1 : disconnect cable from main board to power supply
plug in ac cord if backlight stays on leds and power
board is probably good.If not power supply or leds are bad .
symptom tv on and off slight flash of backlight.
test 2 : remove ribbon cables / cable between screen and
main board with power board connected . turn on if backlight stays on the screen is shorted .