on my samsung u can change an option to do standby mode upgrade and im pretty sure it turns your tv on everytime if this is set to anything else other then OFF even if there is no upgrade.
press menu, then go to the bottom one "support", then go to software upgrade and make sure next to Standby mode upgrade is set to "OFF"
you can set it to either: 1hr after turn off, 2hr after turn off, 2pm, 12pm or 2am.
check that this option is turned off.
if this is set to off or it dosent change it, go to the samsung website and find your tv model then download and install the latest firmware update
if that dosent fix, it most likely is a faulty power supply failing, but if it is always on a certain time it may be the standby mode setting that malfunctioned