Kitchen Small Electric Appliances - haunted microwave

We have a Sharp R420 countertop microwave. It seems to have adopted a ghost. Infrequently, the unit will turn on for a few seconds (lights and motor running) and then it will turn off like nothing happened. One the rare occasion that I was standing next to it when it went on, I opened the door and it stopped. Sometimes it happens when no one is nearby and other times it will turn on for a few seconds right after closing the door.

My wife is concerned that it will turn on like this when we are asleep or not home and end up causing a fire. I tend to think that it does not stay on for very long or have this symptom very often so either leave it alone or decide what to do if it gets worse. The unit does work very nicely when we use the keypad.

Any suggestions on what to do? Does it sound like the control board? Seems like poor judgement to spend money on parts when it is already 5+ years old. An identical model new is about $140 and I already put out $25 for a replacement wave guide cover so another $100 for a controller or other part is not my idead of money well spent. I guess the main question is if this is a dangerous condition?

You answered your own question.It's not worth repair especially including diagnosis.It's probably the switch but still....time for a new one.