Hi @mycatginger ,
My initial thought is the control board only because if it was the control pad, then, to my mind, the light, fan and turntable would also operate because the control pad doesn't control these functions. (don't know your model so maybe the light but not the others). It just sets up the control board and the start button sets it going. If it was the start button on the Control pad for example then I'd assume that 'all' the functions, light, fan turntable would work, when they shouldn't.
This all may be a moot point as I cannot find your model number listed in any of the Kenmore appliance spare parts suppliers available online. Neither SearsPartsDirect or AppliancePartsPros or RepairClinic recognize the model number even though the model number is correct as I found the User Guide for it. You could try calling them to see if they do have parts but they are not listed etc, or whether they know or not that the model is no longer supported for spare parts
It may be that there is a relay on the control board that supplies power to the magnetron and its contacts are stuck operated I don't know as I cannot find a schematic for the oven, (there isn't one on the inside of the oven cabinet is there?) so this is only conjecture