Microwave Oven Failure: Spontaneously turned on… by its LED display
My microwave oven started to malfunction at around five years old. It started to randomly power on the lamp, fan, and turntable. It progressively got worse over several weeks until it was mostly stuck on. The microwave oven is not usable when this happens: It behaves as if the door were open, causing the control panel to ignore button input and to stop cooking if it was cooking.
The obvious suspect is a failing door switch, which is a common cause of failure. There are three switches in the door, and a failure of one or more of them can cause strange behaviour when not all three switches agree on whether the door is open or closed. However, all three switches were tested to be in good working condition, so the most obvious reason is not the cause of this failure.
My microwave is an Insignia NS-MW09SS8 (a Best Buy brand), which is manufactured by Midea (FCC ID: RSFXM925AYY), with model number EMXAUXX-05-K marked on the circuit board inside. There are many other brands/models that use the same internal components. Unlike most similar models, mine has a blue LED display.
Spontaneously turning on is apparently not an uncommon failure. The one-star reviews on the Best Buy website for this model has almost 40 reports of this exact symptom. Many people (unnecessarily) worried that spontaneously turning on was a fire hazard. None of them seem to have found the root cause.
What went wrong?
The microwave “turning on by itself” was caused by an aging/failing LED display. Yes, really.
This unexpected conclusion is worth a blog post explaining exactly what went wrong, why it causes the observed symptoms, and how I repaired it.
This is a summary:
If the lamp is on and the door is closed, the turntable and fan also turn on. The magnetron stays off, so there is no fire hazard. This is expected behaviour.
... continue reading