We are full-timers and our microwave is starting to go. There is a relay or something that keeps the unit on after it is supposed to shut down. After giving it a couple of quick slams on the side it...
We replaced ours with one from Walmart. As long as its dimensions fit the cabinet you can do the same ... unless you don't have an outlet nearby. Also, make sure the amperage on the new microwave doesn't exceed the amps limitations of your rig.
The metal facing on our cabinet had to be removed before we took out the old one. Stuck the new one in its place, plugged it in, screwed the metal facing back onto the cabinet and all was copacetic.