First, make sure that the touchpad is working properly. If the touchpad is working properly, the main control board is likely at fault. If the control board is defective, replace it.
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UPDATE 12/20
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If your microwave continues running when you open the door, it may be a problem with the door interlock switch. ... The components that could stay on when the door is open, but the door switch isn't working are the fan motor, stirrer motor, and interior light.
First, make sure that the touchpad is working properly. If the touchpad is working properly, the main control board is likely at fault. If the control board is defective, replace it.