Presume you've checked through these troubleshooting steps:
• Ensure the Sleep Timer is set to Off in the Setup menu.
• If your PC is connected to the TV, check your PC power settings.
• Make sure the AC power cord is plugged in securely to the wall outlet and the TV.
• When watching TV from an antenna or cable connection, the TV will turn off after 10 - 15 minutes if there is no signal. (Related to that there may be a timer on a set-top box causing this too.)
Unsure if a software update would help as beyond the stuff outlined above, TV power issues have a tendency to be more hardware related. However, to see if a software update could help you out here, what's the current software version on your TV?
Edit: Latest software version available to download from the Support page here is T-TDT5DEUC-1024.1.
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