Hi, got an issue with our TV. Picture/sound breaks up/flashes on regular basis to point where it's not watchable. Worse when it goes dark. Done diagnostic check on "Settings" but won't complete Port test. Port settings are - Port80 & TCP 7288. Know its not TV unit because no problem watching Freeview TV. Had engineer out & when he left all OK. Within 90 min back to picture break up. Suggestions appreciated.