Screen has started to flicker constantly. tv is 9 months old. When switched off flickering stops for about 5-10 minutes and then starts again

The power supply needs to be replaced. In some cases you can turn down the backlight level and the flickering will stop.

I had the same issue occur on my ln55c650 and they had to replace the power supply pc-board. Seems some issue with power module in the TV rather than the side panels. Luckily for me, TV was still in warranty.

Same here. TV back-light would flicker occasionally. Sometimes it would stop and other times it would not. This is the only TV I purchased with a warranty (because I bought it online and got a great deal). The Samsung repairman came out and changed out the circuit board that has the power supplies for the back-light. Total time was 10 minutes to fix. Apparently this is a known problem with some of their TV's. He said the vendor for the power supply transformers had issues and they have since changed vendors. The flickering is caused by one of the transformers failing (it has 2 to power the back-light).

*NOTE: even if your TV is not under warranty call Samsung directly. They should still do the repair for free according to the repairman. Just tell them that you have seen postings on the internet about this problem.