What are the signs of a bad microwave?

What are the signs of a bad microwave that needs repair or replacement include several symptoms indicating magnetron or control failure. First, not heating food even though it runs, light works, and turntable turns, most common sign of bad magnetron at 50 to 100 dollars or high voltage diode at 10 to 20 dollars that generates microwaves, food stays cold after 2 minutes. Second, loud buzzing, humming, or grinding noise during operation due to magnetron failing or high voltage transformer failing or turntable motor failing. Third, sparking or arcing inside due to food splatter on waveguide cover that is mica plate on side wall, clean cover, if sparking continues, waveguide damaged. Fourth, door not closing or not latching and microwave not starting due to door latch or hook broken at 20 to 40 dollars from slamming, safety interlock prevents operation. Fifth, turntable not turning due to turntable motor failed at 15 to 30 dollars or coupler cracked. Sixth, burning smell or smoke during operation due to food buildup or magnetron overheating, unplug immediately. Seventh, control panel buttons not working or display blank due to touchpad failure at 40 to 80 dollars or control board failure from power surge. Eighth, microwave runs but stops after few seconds due to door switch failure. If microwave is over 7 years old and needs magnetron replacement over 100 dollars, replacement is more economical as average lifespan is 7 to 10 years and new models cost 80 to 350 dollars.