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My mother brought me this ultrasonic thingy that is somehow used on your face. The problem appeared pretty simple, just a visibly broken wire. It got more interesting when I opened it up though.

First, the reason it stopped working was because the red wire(assuming DC+) was broken. The black wire (assuming DC-) was fine.

There was also a brown wire that had broken off right at the solder point, I'm guessing it was the ground since I found the little nub it broke off from on the metal plate that runs throughout the whole thing and comes out the other end for the face touching.

I marked them here

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The unmarked blob of solder (at top left) is also on the metal plate but appeared to be unused.

Then when I was stripping the wire, I found another wire that was cut off right where the other wires were previously stripped from. It is blue and there was no remnant of the rest of it inside the device. Not sure whether it was cut off on purpose though since its tip was slightly stripped and looked like the result of a wire being cut from wear and tear.

Anyways, the device works even with only the red and black connected. I also soldered back the brown one to the plate. Should I just ignore the blue one though?

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    \$\begingroup\$ Given the visible quality of the build I wouldn't let this thingy to be any near my face... \$\endgroup\$ – Eugene Sh. Mar 3 '17 at 19:26
  • \$\begingroup\$ Might just be a spare wire that was cut off short. The manufacturer may have used a standard cable with more wires than they needed, or the design may have been changed after the cables were made. \$\endgroup\$ – Bruce Abbott Mar 3 '17 at 20:03

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