Microwave fan stopped working

Our Whirlpool microwave’s fan just stopped working. It makes a humming noise when we turn it on, but the fan does not work. I do not know if it is still heating, but it sounds bad and I do not want to overheat or burn out the microwave. We had a repair guy out and he said that we just need to replace the fan motor, but he did not even take the microwave down from under the cabinet and you cannot get to the motor to look at it. Do you think that is the problem or might it be something else? I am pretty handy and I am willing to take the microwave down and either replace the fan motor, or something else…but just want a few people’s input that know what they are talking about! Thanks for your help!!!