Oven Not Staying at Temp

The range is a double oven model. The top oven will heat up, but then not hold the temp. Bottom element does not come on. Same thing happened about four years ago and I think that the control unit (clock) was replaced.

Is there an easy way to troubleshoot to find out if it’s the burner or control board? Is this a problem with Maytag? Should it still be covered by the parts warranty?