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Defective PCB-mount Switches

Defective PCB Option Switches This type of switch is a nice alternative to the ordinary pin-header option jumpers: pull the white plunger up to open the switch, push it down to close. Nothing to lose or (worse) drop into the machinery.
Being that sort of bear, I test most components, particularly surface-mount parts, before soldering them onto the board. Switches, however… well, what could go wrong?
Unfortunately, both of these switches were defective.
The gutted switch at the top of the pictures stuck open after I soldered it in place: pushing the plunger down didn’t do anything at all. Leaning rather hard on it didn’t get its attention, so I unsoldered and tore it apart. The parts looked OK: no obvious corrosion or deformity.
I tested the second switch, found it worked perfectly, and soldered it in place, whereupon it failed just like the first: stuck open.
Perhaps the soldering iron’s heat (immeasurably) reshaped the plastic or (invisibly) oxidized the contact point? Maybe the design is close enough to not working that installing it pushes the tolerances over the edge? I’ll never know.
These were surplus parts, so there’s no recourse, but I’m pretty sure they’d misbehave the same way if I’d paid full retail for them. If you see any inside your widgets, this may be why you can’t select an option… or why the widget suddenly enters a mysterious new mode.
I tossed the rest of my supply in the trash.