Problem with control board?

Got PRB error when baking. Purchased new power/relay board and installed. Now get F4 code (temp sensor open) upon power up and, after clearing, as soon as hit buttons for bake, broil, clean, etc. Replaced temp sender. No change. ERC no longer available. Picked up "used but tested good" board from tech who parts out appliances he picks up in his work. No change. Picked up new, membrane panel and installed. Still, no change. Have used VOM & built in diagnosis along the way. Indicateds issues on bake, broil and door latch cycle. No resolution in sight. And, techs I've called can't promise anything but billing me for time and one - not particularly technical IMHO - suggests "throw in towel and buy a used oven from him".