Jenn-Air Slide-in: No Display; Fan on

I have a ~17 year old Jenn-Air electric slide-in downdraft range. The oven and burners work fine. Although the touch pad works (e.g. for setting time, type of oven function, fan, temperature), there is no display. The exception to this observation is that on occasion, if the grill is on for a long period of time, I can see a dim display. In addition, to the display problem, I hear a fan (but it doesn’t appear to the the downdraft fan or convection fan??) when the oven temperature is around 200 degrees. When the oven is turned off, the fan will stay on until the temperature falls to around 200 degrees. I have lived with these quirks for several years, but I would now like to fix the stove. What tests do I need to perform to determine what component(s) need to be replaced? In the distant past, boards were replaced, but I do not recall what they were.