I got a cheap Chinese headlamp to see whether I can fix it and I need some help from experts. The headlamp is powered by two 18650 batteries. The problem is the light turns on when I insert only one battery and the switch does not work. Also, the LEDs that indicate charging glow red and green at the same time. Inserting the second battery does not change anything. Looking at the circuit board, there appears to be something melted bottom right...?

 

That looks like someone has had a soldering iron on it and shorted out a resistor for the leds, probably a 330 ohms..show the full pcb.

 

That looks like someone has had a soldering iron on it and shorted out a resistor for the leds, probably a 330 ohms..show the full pcb.

There is nothing more to the pcb... AFAIK the lamp is new. I tried cleaning the board with alcohol, looks like it was just flux? I measured the resistors with a digital multimeter: 512 shows 5.1kOhm, 331 shows 331, 202 shows 2k and R250 shows 0.6 ohm, but that may be my multimeter. Can I do anything to test the two black things (5112 and 3KAF)?

 

As far as I see it, the 3KAF is used for charching. When I attach the charging cable, the battery terminals get power and the middle red LED on the pcb lights up, but not as bright as the other two. However, the light is permanently on and the other two pcb LEDs as well. The switch does nothing. So I'm guessing the problem is in the 5112. Am I right? I can't find anything useful on this, so I would appreciate a step-by step guide on how to test it.