Hello , my name is Jack Perhaps I can help you with this problem but first i would have a few questions ;
Is this tv connected to a cable box/converter,satellite receiver,digital converter etc ?Or directly to antenna/cable from the wall outlet ?Do you have other equipment like a dvd,bluray,games etc. connected to this tv ?If so , did you notice this problem no matter what equipment is playing on tv ?
Sorry , had to step out for a while (lunch time).
O.k then you are using only the internal apps .
Does it go dark all of sudden or gradually ?
When this happens , if you open the tv`s menu , does it also show darkened ?
O.k then this is definitely not a normal function no matter what .
At first i was thinking of some sort of screen saver perhaps but this is not the case .
I`m afraid that this tv will need to be serviced , something beyond adjustment is at play here .
Did you buy this tv locally at a place like curry`s or online perhaps ?
If locally then i would contact that store to see if they have their own service center or contact samsung at this number 0330 SAMSUNG (7267864) and they should be able to tell you where is the samsung ASC (authorized service center ) near you.
Just have your paperwork (serial number, date of purchase etc.) handy when you call them
You can also look at their webpage at the link below;
Wish i had an easier solution for you today like some sort of reset but not the case i`m afraid.
Hope this still help somewhat and please take the time to rate my answer positively (use the smiley) if that answers your question as it is the only way i get paid for helping you , otherwise do not rate at all , just let me know and we`ll see what can be done.Note that you can reach me here at any time after rating if you have questions.
Thank you and good luck with your warranty claim