Adventioneering

So awhile ago my SureFire A2 stopped lighting the incadescent (bright) light. Only the LED lights would work. Since then it’s been sitting on a shelf, gathering dust in an albeit civilized sort of way. I figured the batteried were bad (when they run low, the LEDs work for another 6-8 hours so you can still fly the plane home).

New batteries didn’t solve the problem; so I thought the bulb was burned out, and I had noticed these tungsten deposits which I mistook for a burnout. Shorting the battery to the case lit the regular light, though, proving the tailcap was the problem.

It turns out the weird two-stage tailcaps in the A2 aren’t readily available, although probably SureFire will make them available for three figures. These flashlights also have a lifetime warranty so I could have just sent it in I am sure. Impatient, I broke the tailcap apart instead.

The design turned out to be sort of surprising. There are these little metal tabs. When they make contact with the barrel (ground) they close the negative on the battery to the case via a 10ohm resistor. This causes the LEDs to light but not the main bulb. When you screw the cap down more, the tabs are supposed to bend down and make contact with these copper pads, causing a full short, lighting the main bulb.

My little metal tabs were broken. Really. All three of them! This is bit of a hokey design, given that moving little metal tabs always break sooner or later. What I don’t understand is why they did it like this at all; because instead of the two-stage metal tabs, all that needs to happen is the copper pads need to be raised up enough to contact the barrel (providing the full short). I fixed this in about 2 minutes by soldering blobs onto the copper pads, raising them up from the PCB.

Problem solved!