Hi, have a Seiki 40" LED TV, 9 yrs old, how many diodes have to burn out to get a black screen? mine works a little with a flashlite, trying to figure out if only 1 diode or 1 strip can cause black screen, want to figure out if TV is going to be worth repairing before I spend money on a LED tester or back lights,seems my back lights no one has,or can order, but I can get them in China