http://www.samsung.com/au/support/model/LA55C750R2FXXY

When faced with a machine that doesn't want to give up what part is bad, an grey haired tech (you know they're good since they didn't pull out their hair over the years!) said this: "Replace the cheapest part first."

As a TV tech I take it you already have been through the service manual so this is what's next.
Bob