Electric Oven erratic operation - works sometimes

Hi,
I have a Frigidaire Professional Series double electric oven. The lower oven works fine. The upper oven works inconsistently. Sometimes it will not heat at all, other times it heats to the wrong temperature, other times the bottom element will heat, and still other times both elements will heat. I changed the elements and that did not fix the problem. I suspect I may need to replace the control board, but not sure which one to replace. The clock, timer, etc., all function properly. The only issue is with erratic operation of the top oven. Any help is GREATLY appreciated!