Power LED lamp repair 

My father bought a second hand high power lamp powered by 3 18650 cells.

Unfortunately after installing the batteries there were no way to turn it off.

I have opened up with: "worst case I will put a switch to it" in my mind.

The circuit inside is simple: basically an SOT-23-6 IC marked with 819L 48 a power P fet in SO8 package and some current limiting resistors:

After doing some google fu I ended up on this website:

It turned out that the IC is a Shenzhen Fuman Elec FM2819 The datasheet is only available in chinese, but pushing through the google translate did not helped either.

I have noticed one thing: there were an unpopulated 0603 place parallel with the pushbutton. The russian blog mentioned above that he have had found a cap in the box fallen from the same place. I have followed his advice put a 0603 100nF cap there and now the lamp works as expected.

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