You will solve some of the problem by the way you clean up the area. Most of the cleaning products we use leave behind residue with a smell similar (to cats) to that left by another cat.....so along comes your cat & smells that 'someone' is trying to muscle in on his terratory! So, he re-marks (with urine) that this is his house. You need to clean behind the TV with a solution of biological washing detergent which will break down the 'smell' part of the 'message'. Then, when dry, spray the area with surgical spirits - unplug the TV the night before so the capacitors can discharge & air well before you plug in & turn on the TV to avoid setting alight the spirit fumes with a spark!
Then you could try deterring him from even visiting that spot by using something that he doesn't like the smell of like citrus peel, an air freshener, essential oils on a cottonwool ball or piece of cloth or bought in repellent. Physically preventing access to that spot will also be effective but possibly not very convenient! Or you could try a pheramone spray from the vet. They cost around �15 & come with full instructions on changing both urine marking & scratching marking behaviours to more accetable facial marking.