About 3 weeks ago while cooking, a fan came on and we coulld not turn it off . It sounded like the exhaust fan but no switches could control it. Now, when I try to use the unit, it shuts off after 1 second and says to reprogram the clock. I will do this but the same thing occurs. Did something get too hot that time and burn out?
Remove the top grill, open the control panel and start the microwave with the control panel hanging on its bottom hinges.
If it will do the same thing, replace the control board.
If not, replace the magnetron.
Here are the breakdown diagrams and Replacement parts for MAYTAG MMV5207BAS Mwave - Mounted Over Range/wo | AppliancePartsPros.com
Gene.