Model UN55C6400 UN55C6400RF UN55C6400RFXZC
This TV did not turn on and would click every few seconds.
This youtube video indicates to check for shorts on transistors for the LED drivers on the power supply board.
Power supply board is BN44-00358B. Schematic is available online here
There are 4 transistors Q9101, Q9104, Q9201 & Q9204 and I found one shorted and previously replaced. I ordered replacements on Digikey part#FQU5N40TU-ND (Mosfet N-CH 400V 3.4A Ipak) and replaced all four proactively.
This board may also have an issue with blown fuses which means you should check QP801, QP802 and CP808 for shorts.
After replacing the transistors, the TV powered up but one side was dim. This was traced to loose connections on the LED connector.
Update: The TV came back with a dim side again which I suspected was a power supply fault. I ended up buying a compatible substitute board from the Chinese company buyqual.com which ended up fixing the problem.