I didn't realize this was a TV (My fault) . Most of those have all the LED's in series, and if 1 dies, they all go black.
So I seriously doubt it's more than 1 LED, but you usually have to buy them a strip at a time. EBay is a good source for that. But if you do it, you better have the hands of a surgeon, and make VERY sure every thing is not only put together in the exact same way, (there are a lot of thin flat panels, that have to face the proper direction, reflectors, diffusors, etc. Actually, you need to buy all strips, it sounds like 4 in your case, or the lighting will be uneven. Newer LED's put out more light, so 1 led goes bad, and you need all the strips.
I have done this a few times. Is the Pic dim or barely there at all?