Microwaves run on a cycle, just like a washing machine. Inside the oven is a magnetron that emits waves of energy at a frequency of 2.45 GHz (gigahertz). When these microwaves come into contact with food, they cause the water molecules in the food to vibrate, creating friction and thus cooking your food.
If your microwave's working correctly, then you should expect some hot spots as that is how it works. Some microwaves may not have hot spots due to their design or heating mechanism (e.g. inverter models), but this shouldn't affect the quality of cooking.
When your microwave is putting out too much or too little heat, however, it can be a different story. Several things could cause this problem. For example, if there are small holes in the door, then some microwaves will leak energy and not cook food properly. If you've already tried to seal up these holes with duct tape, then the problem may lie elsewhere. Here are five of the most common microwave problems and how you can fix them.
1) Food isn't cooking - The door is letting too much energy out
This probably means that your microwave needs to be cleaned. Food particles will build up over time and can cause the door to let out energy. Clean the microwave thoroughly and then dry it with a clean dish towel or paper towel before using it again. You can also use vinegar and water to get rid of food particles, but make sure you don't get any on electrical components (e.g., magnetron) while doing so unless you want to make your microwave explode.
2) Food isn't cooking - The door is letting too much energy in
If the food isn't cooking, but you've already checked to make sure there aren't any holes or cracks that could be letting energy out of the oven then check to make sure that you're following the proper cook times and power levels. Also, make sure you're using the proper cooking utensils (e.g., ceramic dishes for microwaves with lower wattage) and that your food is in the appropriate proportions (e.g., don't overfill the dish).
3) Food isn't cooking - You smell smoke or burning
This means you either have a problem with the magnetron (i.e., you're burning out the filament) or the timer is broken. First, try to reset your microwave by turning it off and back on again as this may solve the problem. If that doesn't work then you need to contact a service technician as something else probably went wrong beyond what can be fixed with a simple reset.
4) Food is overcooked, even on the lowest power setting
This means you should check to make sure that your microwave's rated wattage matches what the pre-programmed buttons indicate and then check your cook times and power levels. The problem may also be caused by a faulty door or timer, so you'll need to check those as well.
5) Food is undercooked, even on the highest power setting
This usually means that there's something wrong with your magnetron or timer. First, try resetting your microwave by turning it off and back on again as this may solve the problem. If that doesn't work then you need to contact a service technician as something else probably went wrong beyond what can be fixed with a simple reset.
Now you know how to fix the most common microwave problems! If you're still having trouble, try consulting an appliance professional!