Our Panasonic microwave claimed to be state of the art by virtue of using a high frequency inverter to drive the step-up transformer that feeds the magnetron tube that generates the microwave energy to do the heating. So far so good. That portion may actually have been designed by a real engineer, although I am certain that the real reason for using the inverter is to avoid the expense of the high voltage transformer.
The moment of grief came when I returned home one afternoon, and my wife informed me that her breakfast was still in the microwave because the door would not open. I tried the button to release the latch and found that it had no resistance to my push, which convinced me that the linkage inside had somehow failed. Thus, the next step was to open the housing and see what had failed, and how a repair could be made.
Panasonic evidently believes that the housings of their products contain private materials that others should never see. The screws holding the cover on were the security TORX type that have a post in the center of the star. Fortunately, my security bit set from Microcenter had the correct bit to match, so the effort to keep me out was thwarted, and I removed the cover. While the screws on the back were the security style, the ones on the side were plain Philips style. So now the unlatching mechanism was sort of visible, but only a small part of it.
The majority of the mechanism contains three limit switches; two are implemented to open the AC line supply if the door is not totally closed. The third switch is wired to short circuit the input to the high voltage supply until the door is completely closed. I already knew that -- they are all that way. There was no circuit diagram inside the cover. And, there was no list of parts, replacement or otherwise.
I decided to remove the assembly without disconnecting the wires, since there was nothing to help get them back in the correct positions. With the unlatching assembly removed, a detailed examination revealed no worn or broken parts, and nothing out of adjustment. Yet the door was still latched shut. Reinstalling the assembly magically unlatched the door. Closing the door resulted in its latching again and not being able to unlatch it with the release button. But a clever poke with a long screwdriver produced the needed unlatch. So what was the failure that caused the problem?
The design of the latching system is unique in that the latching and unlatching are done by completely separate mechanisms. There are two barbed hooks that extend out of the door at the latching edge, and these barbs hold the door closed. As the door closes they ride up a cam surface inside two openings in the front of the oven, and when the door is fully shut they slip down beyond the end of the ramps and securely hold the door closed.
The upper one of those barbed hooks was extending the correct distance, while the lower hook, which is the unlatching mechanism, raises to allow the door to open. It was not extending nearly far enough, so the unlatch mechanism was unable to move it upward and unlatch the door.