Staying on the theme of lights and switches, I have a sequel to my previous household light switch teardown: a double switch! This unit was retired and replaced by a new unit once one of the two switches (the lower one) could no longer stay off.

On the left, both switches are in their "On" position, and this is fine. On the right, top switch is in the proper "Off" position, but the lower switch could not do the same. If I flip the lever to "Off", it doesn't stay there but would move back a bit. Sometimes that's still electrically off, which is fine. Sometimes it springs back to electrically on and I have to try again, which is annoying. But the real problem is the rare case when it stops in an unfortunate middle ground, and I can hear a lot of popping noises consistent with sparks/arcing inside the switch. Very bad! I replaced it promptly to avoid risk of permanent electrical damage. After it was replaced, I want to see exactly how the switch mechanism failed.

On the back side of this unit is a rivet-like structure, surrounded by text PAT PEND (patent pending?) and SPEC GRADE. I have no idea what spec it met the grade for, but I know this rivet has to go.

After drilling it out, its front facade was still held by four plastic clips. When I pried that face open, it was a sudden release and everything flew apart. Several pieces of metal landed at various places on my workbench. I think I found them all, but where did they used to live, and what were their function?

Two large pieces remained inside. They look like they carried power, with a rounded contact pad at the end. Two of the metal pieces that fell out have matching contact pads and wiring screw terminals, they must make up the rest of the power-carrying circuit. The lower pads are more charred-looking than the top, consistent with suffering a few arcing episodes, but other than that both sets look identical and would not explain the problem.

My hint came from looking at the lever's back side. There are actually two levers sticking out. The shorter wider portion pushed on the large electrical bar, and the longer narrower portion pushed on something else. Process of elimination says it must be the two remaining pieces of metal that fell out.

Those narrow pieces of metal must have mounted to the side of the enclosure on their flat ends and acted as springs that held the lever in one position or another. When holding their flat ends together on the tabletop, one of them is visibly more tired. The weaker spring could no longer hold the switch lever in the off position.

So the switch was electrically fine, it was just a worn out lever spring. Would it have resumed working if I could manually bend the spring back and reassemble the switch? Maybe, but this double-switch was not designed to be repaired. After I drilled out the center rivet there was no secure way to put it back together safely enough for use.

It's fine, it served its purpose over many years. And amusing enough, its replacement served one final purpose: letting me know my UPS batteries are no good and I need to buy replacements.