Question: I've had [a cheap 18650 flashlight](https://de.aliexpress.com/item/4000396427849.html) for some time now - when turning it off and on, it cycles through five modes - full power, medium power, low power, strobe, SOS signal.

I'd like to disable that feature and just use it in full power mode whenever I turn it on.

[![enter image description here](https://i.stack.imgur.com/KnxtV.jpg)](https://i.stack.imgur.com/KnxtV.jpg)
[![enter image description here](https://i.stack.imgur.com/c4xUu.jpg)](https://i.stack.imgur.com/c4xUu.jpg)

I assume the "HL6S2" component controls those modes, but I couldn't find any useful information on that.

Positive power comes through the via near the red lead.
Ground is on the perimeter of the chip.
The flashlight is turned on and off via a switch on its back, which connects the case to the battery ground, so the IC seems to have some sort of memory to retain its information for prolonged periods of time.

I assume the IC switches the left leg (connected to the blue lead via two 500 Ohms resistors in parallel) to ground, which is on its middle leg.
Does anyone have a datasheet for this chip? Searching for the markings wasn't very helpful.

To mod it, I'd remove the IC and solder a bridge from the left to the middle port - does that sound reasonable?

Answer: 
The IC is an ASIC with built-in power transistor. You can do nothing with it, but bypass it.

Here is a similar part:

[![enter image description here](https://i.stack.imgur.com/HPyTP.png)](https://i.stack.imgur.com/HPyTP.png)

That one has 3 functions plus off (100%, 25% and flash), as clearly described in the [datasheet](http://www.hmsemi.com/downfile/HM5101.PDF). It also reverts into a low power mode to save the LEDs when the temperature is too high, and is protected against reverse battery.

Those resistors are 0.5 ohms, not 500 ohms, by the way.

Presumably if you can **measure** the forward voltage at 100% power you can replace the chip with a resistor. It's possible they've got an amazing n-channel FET in there with negligible Rds(on), as your 'just short it out' comment suggests, but I would not count on it.
Since you are on this site, curious and inquisitive, I assume you'd much rather modify the design, rather than work 2 hours in a menial job to buy a different flashlight.

So what you could do is use the push button to switch it on (100% was the first mode in the cycle?), and for switching OFF you could solder a second "normally closed" push button to cut off power from the battery. This would work if the flashlight powers up in OFF.

Should it power up in ON, then you'd have to use a normal toggle button in replacement of the current one.

But if it doesn't start with 100%, then you'd have to replace the whole control unit with a resistor to set the current, or use a regulated current source.

The resultant joy and satisfaction from making your own mod can never be supplanted by any amount of cleaning or burger flipping.

I also think this is the reason whay many of us are here, so you are in good company.