sharp lc-43cug8462ks backlight has no power but leds are all good

hi I have a sharp lc-43cug8462ks the backlight has no power.i can see a faint image on the screen with a light and I have tested th leds and all are good so I tested the power board.i tested the plug that powers the leds and was getting a spike or around 110v down to 0.3v in about a second so I thought the power board was faulty and fitted a used one from ebay.but now fitted am still getting the same reading? any help and information would be greatly received thanks.