Samsung UNF series TV: why screen flickers black (backlight failure)?

Samsung UNF series TV: why screen flickers black (backlight failure)?

My Samsung UN40F6300 has been repaired three times. It's now out of warranty, lightly used, and has developed a flicker. The screen quickly fades to black for less than a second, every 5-30 seconds at random. Sounds like a backlight is going out. Can anyone help diagnose?

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