PLX Luxor flashlight

[samverstraete]

Hi, this is for all the owners of a PLX Luxor flashlight. You might run into the same issue I ran across, because, in my opinion, this is a design flaw.
I love my Luxor flashlight. It has everything I want: firm grip, bright when needed too, but dimmable to last longer, big LiPo battery, focus adjustable to almost 360°, display that has all the info, … So I was very unhappy when it didn’t work anymore and decided to try and fix it.
At one point I noticed my flashlight was turned on. I couldn’t turn it off anymore and when I reconnected the battery it turned on, but the buttons didn’t work. Reconnecting the battery resulted in the flashlight sometimes doing nothing at all or turning on but not reacting to any buttons (not even turning off).

I played around with it a bit and then noticed when I pressed the function button while reconnected the battery, ‘locked’ would show up on the screen. In a normal situation you can lock the flashlight by simultaneously pressing the power button and the function button. So that means that the power button somehow was stuck. I opened up the flashlight. One tip: unscrew all screws, also the ones near the buttons, the main pcb and button pcb come out to the button-side, the plastic holder to the other side. I only figured that out when I removed the main pcb to the other side, bending over all the buttons while doing it.

The power button circuit is pretty easy. Basically it is an pull-down circuit using R13 on the high side and the button on the low side connected to GND. It looks like the trigger is connected on two places to the microcontroller. And by the way: scraping off the partnumbers on the IC’s… common guys, that’s just silly.

The repair:
So… There’s 2.7V at one side of R13, that seems to be the supply voltage and 1V at the other side. R13 measured a bit shy of 10k so 0.1mA is going through it. Now 1V that’s really on the edge and it’s bad practice the use that voltage to trigger something. Either somehow my micro is consuming too much or R13 is a bit too high. So I decided to solder another 10k on top of it, making it 5k. And magically the power button and thus the flashlight worked again as before.