Q:

How does a microwave door interlock work and is a DIY repair feasible?

Our microwave has developed a problem.  If the door isn't shut just so, the microwave thinks that it is open.  The door can be shut too lightly or too hard to exhibit the problem.  Recently it has began to pause right in the middle of cooking because it thinks the door has suddenly opened when it is still shut tightly.
From what I've read, the problem is likely with the "door interlock", a kind of sensor (or multiple sensors) that let the microwave know when the door is open or closed.
How do these sensors work, and is it possible to fix them yourself?  (I don't mind taking things apart.)
The specific microwave in question is a GE Profile PVM1790 over the range model.

A:

This particular model has three microswitches to detect the door being fully closed.

If any one of them are loose or defective, it would cause the symptoms you experience.  Each switch is pricey at $30 from GE or $23 from Amazon but there are many low priced sources (see comments below), so I would open up the appliance and have a look to see if a wire has come loose, or a switch is no longer seated properly.  With it open, you should also be able to trigger the switch and see if it sounds like it is working correctly.  With this type of switch, listening to it can successfully diagnose them 90% of the time.
If all the switches seems mechanically okay, then bust out a DMM and use the ohmmeter to see which one is not remaining closed when toggled.

A:

The door interlock circuit is typically at least 3 microswitches which have to close/open in a specific sequence and arrive at a specific end-configuraton to convince the controller that the door was actually closed properly, rather than a crude attempt at bypassing the switches being made.
The switches themselves are normally very reliable (they are one of the nearly always salvageable parts of dead microwave ovens) but if the door-latch has worn or broken it may not contact them correctly.
In short, I suspect the sensors (switches) are probably fine, but the mechanical parts that actuate them are more likely to be the problem.
As for testing the switches, just check for continuity - the NO contact should be not connected until the switch is pressed, the NC contact should be connected until the switch is pressed, and both should change to the other condition when the switch is pressed. Pay attention to what wires are connected and where the switches are - it's typical for a contact to be cut off if not used, and which switch goes where (and which wires connect to it, where) are important for the whole business working correctly.

A:

I haven't looked up your specific model but every modern microwave I've taken apart has used a micro switch, they're so commonly used that people refer to them as microwave switches now.

They come in a few different configurations and sizes but only cost a few bucks, you can find them anywhere from RadioShack, Sparkfun, Mouser, Digikey, etc. I'd take a look inside the microwave before ordering but should be a fairly easy DIY if the switch is gone. If the place where the switch mounts is broken or the plastic pushing it is broken you may need to buy an manufacturer part at that point.

