We let our boys take apart broken appliances. They LOVE this. I count it as part of their grand and beautiful education. When a boom box I've had since (muffled year) finally gave up the ghost, the boys saw it in the trash and claimed it as their own.
They've learned that boom boxes are made to be put together, not taken apart - but this has only heightened the intrigue and mystery. They've learned what makes the cassette doors open and holds them closed, how magnets come in to play and a million other little things I'm sure. Just about now, it's demolition is ready to be swept away for good but they have salvaged parts to build their robot using a knex motor. I can't wait to see it.