Replacing a stirrer belt
NOTE: Before you begin any microwave repair, including this one, make absolute sure you unplug the microwave and discharge the capacitor first.
To get to your stirrer and stirrer belt, remove the outer cabinet. The outer cabinet is usually held in place with just a few screws. The stirrer belt will be on the very top of the unit under the cabinet, and will be easy to identify.
Before you go ahead and replace your stirrer belt, first examine the part to make sure there is no debris blocking its movement. There may be an object restricting its path of motion, and you may not need to replace the belt at all. If you find a blockage restricting the stirrer belt motion, clean it out. Test to see if this has corrected the problem by running your microwave. DO NOT run your microwave with nothing in it.
Next, affirm that the belt is properly installed in the unit. It may not be sitting properly in the correct position, and may only need a slight adjustment for proper functioning.
Remove the belt and examine it for signs of wear. Stretch it out about 25% beyond its normal size. When released, the belt should instantly revert back to its normal, relaxed length size. If your belt does not instantly return to its relaxed length size, or shows other signs of being worn or flabby, then replace it with a new belt. A new belt will slip on the same way the old belt came off.