Problem retaining correct date time



10 year old 32" tube [with converter] fried a power board last week. Purchased a Vizio E480i-B2 'smart' TV but only connected to antenna and DISH. Date/time is auto set by entering time zone and zip code. There is a problem while on 'antenna' mode receiving and retaining the correct date/time. TV keeps reverting to January 1, 1970 midnight. Date /time can be corrected by turning TV off and then back on.
While using remote and clicking 'guide' or changing channel, date/time may or may not be correct time. And if correct date time, it usually shows the last time remote was used and takes a second or two to self correct. All info in the program info pop up box is correct.
Vizio tech support told me that the TV is designed for internet use and a router/modem to get correct date/time.
Some entity in the Tampa FL is sending date/time, the tuner and the system date time program is accepting it. But the TV will not retain it.
I'm trying to determine if there is a problem with the TV or with who is sending the signal.
Anyone know who sends date/time to a TV using an antenna [and especially for Tampa FL]?