Wednesday, May 9, 2012

Princeton Tec EOS headlamp repair

I took two of the three AAA batteries from the EOS yesterday to use in an appliance remote control I had just brought back from the dead. I bought replacement batteries today and when I was about to install them I was utterly horrified to see the lone AAA inside shrouded in white greenish ectoplasm. I quickly removed and threw it away. Cleaned the battery case with tissue and used isopropanol soaked Q-tips to remove the gunk from the nooks. Installed fresh batteries. The headlamp immediately lit up as I put the last battery in. That shouldn't happen and was the first omen that not everything is well. Then when I switched off the lamp it magically switched back on again at full brightness a couple of seconds later. Oh no! It's possessed! And it kept turning back on whenever I switched it. And so exorcism was called for.

To my my initial consternation I discovered that the battery case was held down not by what I thought were torx screws but by heat stakes. I actually tried to carve the heads of the stakes off using the torx screwdriver. No dice. Had to go to the drill press and drill them out, which turned out to be painless--for me that is.

I could see that the chemical spill had reached the circuit board, particularly the ground (negative power supply) solder joint. I proceeded to clean the board with cotton and alcohol. After I was satisfied I installed the batteries. Uh oh. The lamp turned on automatically again. And after switching it off, it switched itself back on.

I suspected that the battery goo must have shorted out some of the vias and/or solder joints on the other side of the board. And I now had no choice--other than resigning myself to removing the batteries every time I'm done with the lamp--but to uncouple the board from the battery case. That meant desoldering the two battery terminals and gouging the four heat stakes locking the board to the case.

I actually thought there were only two heat stakes--yes, my eyesight is really that poor. And that's the reason I had a hard time prying the board off the case. Good thing I didn't inadvertently snap the board or break any tracks.

Turning the board over I immediately noticed that part of the solder mask on the ground trace had been eaten away. Alkaline battery chemical is really nasty stuff! I lost no time and quickly cleaned the board with alcohol.

To test the board I used the 3.3V output of my ATX power supply. Homemade cables with banana plugs on one end and alligator clips on the other conveniently routed power to the board without having to solder any wires. Moment of truth. I switched on the power supply. The lamp didn't turn on! Good sign. I then turned the lamp on and then off. 2 seconds ... 3 sec .. 4 ... 5 ... The headlamp's no longer possessed! You should've heard me singing and doing a jig.

With anxiety level and blood pressure back to normal it was then that I started taking pictures. So all the photos below are after the clean up. I now kind of regret I don't have shots of the ectoplasm-covered battery while it was still in the battery case. Would've been a great pièce de résistance for this horror story.

That's an Opulent Rebel Star 1-watt white LED on its own star pcb. Green board contains all the drive circuitry. Round black cylinder on the left is an inductor. Black square glob on the right is the microcontroller.

White rectangular thing on the top right is the momentary contact switch.

Solder mask partially dissolved by the horrible stuff that leaked out of the alkaline AAA battery. The gold flashing surely prevented the copper from being attacked. The offending battery chemical spill bridged the cluster of three vias and the ground throughhole solder pad.

Another angle of the same. All that glitters is gold.

Who's Azoteq?

The LED lens

The holes snapped into four studs on the battery case

The heat stakes are on the four crosses. The LED lens sits on the four studs close to the center.

1 comment:

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