It should go back to the input - assuming you're using a cable/sat box. If not, the tuner should revert back to the channel it was left on. The only scenario I'm aware of where this might not happen is if the television is in Shop Mode.
Let's see if your television is in shop mode.
Try changing the brightness or the contrast and turning the television off. When you turn it back on, are the settings the same, or did they revert to the numbers that were there before?
Hi Samsung Tech,
I've a LA40A750 model and noticed that when I turn on the TV it does not revert back to my previous TV channel. It normally goes into an analogue TV channel. Do you know what's wrong?