I encountered the following problem with Soundbar HW N550 recently purchased. It connects to a TV through HDMI (out). I connected Google Chromecast through an HDMI cable to the HDMI in for the Soundbar. When I switch the soundbar to HDMI all works fine for few seconds, then a message "PRT" is displayed and after it "Bye" and the Soundbar shuts off.
I found out it is related to the level of volume. When the level goes above 22 the issue happens.
Hey @yoavch! Best thing to do here is to get in touch with Samsung AudioVisual team. They are specialist support in soundbars and will be more than happy to help. You can contact them on this number: 0333 000 0333.