P50pdtv10a will not change channels stuck on channel 3
The system memory IC of your TV has damaged. This is one, which stores all the setting we have done with remote control, including channel memmory. This IC works in conjunction with the main system control IC. When we switch OFF or do any other adjustments with the tV, all the data will be stored in this IC, and tetreived from it to main system IC to process when we switch ON the TV. This is a non-volatile memory chip, ie, even the power is OFF, the data stored in it won't lost. This is a very small IC, can locate very near to main system control IC. Will have 8 solder terminals [normally], and ver cheap to buy too. Even though it is a very cheap and small one, the function of it in the circuit is great. In some Vizio sets, this IC will be of SMD [surface Mount Device] type, and on othere will be a DIL [Dual In Line] type pin confujuration. If your TVs memory is of first as stated above [SMD], replacing it will not be an easy job. If it is of second type, it can be replace easly.
Anyway, this is not a work that can be done without skill. If you have enough knldege in electronics, and have a concept of desoldering and soldering, have all soldering equipments with you, you can do this work by yourself at home. Otherwise you have to seek assistance from an experienced service technician. OK.