Sunday, December 4, 2011

Repairing an ultrasonic cleaner

I love my ultrasonic cleaner, and have been using it daily since I got it almost two years ago. Unfortunately, in the past few weeks it's started to get unreliable: press the button, nothing happens. Try a few times, and usually it'll work, especially with jiggling. Sounds like a wonky connection, but where? I had a couple of ideas: one, that leaving it full of water all the time, in defiance of the instructions to empty it after use, caused something to corrode somewhere. (I'd change the water/soap about once a week, or if I thought it was getting grody.) Or, noticing that the buttons were located on the hinged lid, maybe something having to do with the hinge. Tonight I took it apart. Here are some pics:

View from above, with the lid more or less in place. I've removed the smoked plastic insert which keeps dust out. You can see the buttons on the bottom of the picture, and the hinge on the top. It's a little ajar, since I've already started taking it apart. Also visible is the entirely pointless blue LED light for the chamber.

With the top piece removed. The wire harness connecting the switches and the blue LED comes out of the hinge at the top. No wait: the wire harness, carrying delicate wires without which the machine won't work, *is* the hinge, or one side of it anyway. Oh my goodness. I'd wondered how they'd arranged to avoid stressing those connections inside the moving hinge, there are ways to do that, no doubt. But not only did they not bother protecting the wires, they used the wires themselves as a structural component of the hinge. Probably durable enough to last for the one year warranty period, and no doubt flimsy enough to ensure that it wouldn't last much longer. Kind of a Chinese version of planned obsolescence. The thing is, putting the switches on the lid is totally unnecessary: they'd have worked fine fixed on the body, which would have avoided running wires to the top. The only requirement for a wire to be located up there is for the useless blue LED, whose primary purpose is to make the gadget look "techno" in marketing photographs.

Just for fun, pics of the bottom interior. The big piezo attached to the chamber bottom is the main thing here.

And the circuitry. At the left there are two big transistors attached to a black finned heat sink, this heat sink has a cutout for it which lets it rest near the chamber bottom. The circuitry and the piezo dump enough heat into the solution to get it warm during use. Whether it's just a convenient place to put the heat, or if it's an intentional design allowing the solution to warm to aid cleaning, I'm not sure. You can also see a fuse, a nice feature in an electric gizmo that's around water. In addition to driving the piezo, the circuit has to recognize the on and off switches, and has a timer, to let it buzz for three minutes before stopping automatically. At the bottom is where the wiring harness comes in. If I was going to jumper a new switch in, I guess I could do it there.

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