I have a Samsung Smart TV (UN50NU6950FXZA) which just started
acting up. When powering on it no longer defaults to the HDMI input
coming from the cable DVR box. The TV now defaults to the Samsung
TV Plus app*, which a set of free TV channels provided by Samsung. I
have to manually switch the source to HDMI if I turn the TV on.

*Well, it sort of defaults to the TV plus app. It shows the TV Plus logo in
the upper corner and it displays the name/number of the channel that
it was last tuned to, but it doesn't actually display the channel. The
screen just goes blank after a couple of seconds. If I select a different
channel, it will then display it. When it first powers on it's kind of in a
TV Plus-esque limbo.

I called Samsung and they tried to blame my cable provider's equipment.
When I told them that I tried both a different HDMI cable and even a
different cable set-top box, they were stuck. The only other suggestion
they had was to try a factory reset. Great, now I'll have to reload all my
apps, hoping I remember what password I used years ago, etc.

I'm really just venting but also sort of hoping that someone has other
suggestions to try before I do the factory reset. No, there is no "Default
Power On Source" that needs to be selected in the settings. If there is a
signal at the HDMI port, it's supposed to default to that.