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Archive for August 3rd, 2014

Flashlight Switch: Poor Solder Joints

My desk flashlight has three “functions”:

  • 5 UV LEDs
  • 10 white LEDs
  • laser pointer

A four-click rotary pushbutton switch actuates the three functions (plus “off”) in sequence:

Flashlight switch - internal wiring

Flashlight switch – internal wiring

All three lights became intermittent, which suggested a poor return connection at the far end of the battery. The case is, of course, aluminum, with coarse-cut threads that grate as you tighten the parts. I cleaned the crud out of the threads, anointed them with Ox-Gard compound, and discovered that the laser and UV LEDs were still flaky.

Taking the thing apart and unsoldering the switch connections revealed the problem:

Flashlight switch - bad solder joints

Flashlight switch – bad solder joints

Yup, two lousy solder joints. They’re not exactly cold solder joints, because there’s not really a joint there to begin with; the switch tabs never got hot enough to bond with the molten solder before it cooled.

A dab of flux and touch from a hot soldering iron solved that problem.

Assemble in reverse order and it works better than it ever did before!

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