#Solved
Our microwave has just begun to show a failure mode. With no settings on the timer/modes when we close the door we hear a 60-cycle hum.
We put a coffee cup with water in and closed the door but did not push any button and noted the hum. The water got warm, for the exposure of 20 to 30 seconds, the water got the expected level of warmth we think.
Is there any danger if we leave the door open? (No hum with the door open)
Could the Magnatron be running at a higher output than it is supposed to when the door is closed but the microwave is not under the control of its built-in circuitry?
Of course, there is no danger of the microwave doing anything other than heating stuff (No mad science going on)? We know that microwave ovens work by making the water molecules vibrate faster.
We intend to replace it soon. In the meantime, we will leave the door open. We do not hear the humming sound when the door is open. Do you suppose we should unplug the unit? (nontrivial as the unit is an over-the-stove kind with the plug high in a cabinet above the microwave and of course, in the back of the cabinet.)
