As the posters above have said, Tesco are entitled to offer you whichever of the three (repair/refund/exchange) it deems best value and convenience for all parties. In TV's this is always repair. If the repair does not fix the issue, they will usually give you a direct replacement, or if it's a discontinued model, they will either offer you an equal-spec replacement, or send you back into store with a returns number for a refund.