Fill it with water and nuke it in the microwave oven. The memory in it is probably a PROM, and it won’t be bothered in the least by any magnetic field you could generate. The micrwaves, however, will quite likely transfer enough energy to electronics to toast something in it.
Zev, if you’re going to try the magnet thing, note that you can find a strong magnet at the back of most speakers. (The speaker itself, not the box that it’s in.)
DDG’s magnet won’t be strong enough (no offence DDG).
If the magnet doesn’t work:
- put about a half inch of water in the mug.
- put it in the microwave.
- set the microwave for 1 second, and turn it on.
- check whether the mug is dead. if so, end.
- set the microwave to 2 seconds and repeat step (4), try longer times up to about 5 seconds.
- try something else.
Usually, the maelevolent mechanical musical mischeif-maker is concealed in a plastic false-bottom on the base of the mug. Using a slim-bladed screwdriver/knife you should be able to turn the mug over and pry off the false bottom, remove the gubbins, and re-glue the bottom.
Putting it in the microwave might result in a shower of sparks and the demise of the microwave, due to the presumably metallic electronic components within the mug.
jjimm, cite?
Here you go, Desmo.
And personal experience, too!
Cite in return, jjimm. 
I have done several of these (I blew up an egg only yesterday morning, to the consternation of the wife and the cat) - the soap trick is fantastic too, and you can use the soap as soap afterwards, too.
I see the site you posted recommends a glass of water during each ‘experiment’ to protect it. About 3 months ago, some bozo put a metal-rimmed plate in our company microwave, with a small amount of food in it. In addition to the buzzing and sparking and the pitting of the plate rim, it also disabled the magnetron.
We’ll just have to agree to disagree.
Are you saying that arcing and so on can’t destroy a microwave, or are you saying that the water in the mug in your suggestion will preserve it? From the notes page of your cite:
My emphasis. Or am I being whooshed?
Sorry for the hijack, Zev.
Look, jjimm, I accept that a magnetron may be damaged by being operated without a load. A load in this case is something that absorbs microwave energy.
Arcing on the silver or gilt edging on a plate isn’t going to damage the magnetron, and neither will the arcing inside Zev’s cup.
You aren’t being whooshed.
The rule is “don’t operate the magentron without having something to absorb the energy it produces”.
The easiest way to absorb the energy is to put water in the oven. Metallic traces like gilding or electric circuits will preferentially absorb the microwave energy.
Introduce it to the SDMB. That way it’ll only work for a couple of hours a day.
OK I concur. Must have been a coincidence.
lieu, you’re too right.
I don’t think the magnet or the microwave will make a differnce. The cup is triggered by movement of the cup which means it has a mechanical trigger that has probably gotten stuck in the on position.
Sure it’ll help. If the little computer generating the tones is toasted, then the little switch can stay turned on all it wants - nothing will come out.