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This means that the tv is not retaining its channel setting memory once the tv is turned off which woul require and internal repair. If the tv is not that old you would need to check with your local laws and company provided warranty info as the problem may be covered under the factory warranty.
This is so long as your not only scanning for the channels but also set the tv to scan and add/save them.
If you need further assistance just let me know.
There would be one of two things used, either the power supply supplies a small amount of power at all times for the memory retention or an internal battery small and round is placed on the board for memory.
One way to know is before if you unplugged the tv from the wall/mains and the tv could be plugged back in and still had the channels then it uses an internal memory battery this battery is either able to be removed by popping out or they solder them in place.
If you need further assistance just let me know,