I'm a homeowner with some experience in electronics, and I'm having a problem with my Kenmore Elite Model # 721.80833500 over-the-stove microwave. It's been running fine since we bought it several years ago, but this AM, I tried to cook some bacon using the pre-programmed setting for bacon. After a few minutes, the unit stopped cooking before the timer was done and the display panel said "Press enter". I pressed "Enter" and it started up for a second or two, then shut down. I tried to start it up several more times with the same result.

I tried to start it several more times with no improvement. Then I unplugged the microwave for 30 seconds, hoping the brain just needed to re-boot. Re-set the clock and tried again. No improvement.

I removed the bacon and replaced it with a glass conatiner of water for an energy load and started trying different ways (different keypad combinations) to get the unit to stay on, with no improvement. Now when it shuts down, I get a fast 8 beeps that I assume are an error code.

The way it's acting, it seems like either a temperature or current overload feature that's kicking in. The oven doesn't shut down altogether (everything [display, lights, fan] still works except it doesn't cook), it just shuts down after it starts. Sometimes it runs for half a second, sometimes for several minutes before shutting down prematurely.

I have the Sears Field Manual for this model, but it doesn't address a problem like this in the troubleshooting chart. I was thinking at first that it could be the electronic circuit board, but the schematic also shows a MGT (magnetron?) thermostat, an oven thermostat and (on the circuit board) a thermistor that all seem likely candidates.

Anybody seen this kind of problem before?

Sounds like the magnetron is kicking out on a thermal overload. Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears Parts Direct | SearsPartsDirect.com from Sears has the part for $80. Not necessarily the cheapest source. They have exploded diagrams of the appliance as well.

Replacement is straightforward, but the supply to the magnetronis about 3000 volts, so you have to be comfy dealing with the possibility of charged caps.