The twelve-year-old microwave oven failed last week. Tam bought it not too long after she moved in; my dinky 700-Watt zapper with a balky mechanical timer wasn't enough oven to keep her fed. She got a modern one, 1100 Watts and big enough to warm up a whole ham.* It worked well for years.
Last week, the microwave finished failing: the "buttons" on the control panel have been gradually dying for a couple of month. It's a problem Litton and Amana solved in the 1970s, with non-tactile glass-surface touch controls -- but the solution didn't stick. Membrane switches are cheaper to produce and less finicky.
But they do fail. The "1" and "6" buttons when first, then the whole left half of the number panel and, slowly, all but the rarely-used controls at the top and the "start" and "stop" buttons. It wasn't much of a problem, really. On that model, pressing "start" calls up a thirty-second run and additional presses add thirty more seconds, up to a total of five minutes. If you're mainly using the microwave to bake potatoes and defrost leftovers (the "defrost" button worked until the last), it's not a problem.
Then the "start" button died. Punching around, the only one that still worked was "popcorn," a three-minute, 100% power cycle. That was usable but it was clearly time. I ordered a new microwave and it showed up yesterday.
Why didn't I fix the old one? Membrane switches is why. It'll be a bespoke layout, conductive material screen-printed and fused onto plastic. If it peels apart -- not all will -- you can clean them up, even paint new conductive goop over the old pads, but it's a short-term fix. There's not much to work with there and nothing will hold up as well as the original. It's a hundred-dollar-or-less consumer good. The part that does the actual microwaving? That's all working fine.
The Amana RR9 chassis I remember fondly from having been a tech in the factory of a subcontractor that built the controllers for them, way back before the not-yet-public Internet snuck off college campuses? That thing cost as much as a crummy used car. The limitation was magnetron life, and those were field-replaceable. The controller interface was simple -- power in, switched power out, and a pair of leads for a temperature probe in the higher-end models, all on a Molex connector. In a pinch (or, say, a test equipment maintenance shop), you could replace the controller with a toggle switch; add a pushbutton in parallel to pulse the tube to make popcorn. Sell a family one of those ovens, and they'd have a microwave for thirty years -- if they could afford to buy it in the first place. Which is possibly why cheaper, overseas-made ovens displaced them from the market.
* This is not to imply that Tam considers a whole ham a proper snack. My old microwave, though, wouldn't even fit a some dinners.
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