I duckduckgoed “SOT23-6 boost converter” and found a picture of an IC with similar markings - I’m now pretty sure the component is an FP6291 switching regulator by Advanced Analog Electronics.

If you look on page 3 of the datasheet, the “AL” identifies the part, and the following numbers are the year of production and the wafer lot number, so they could really be anything. The pinout matches as well, given a few inaccuracies in your schematic, which I think I can confirm on the images. Thanks for the image of the PCB against the light, that was very helpful.

Pin 1 would be on the bottom right, connected to the inductor L1 to boost the voltage, with the other pins arranged counter-clockwise. Pin 2 should then be connected to your PCB ground; to confirm, you could use a multimeter in continuity mode to measure to the BAT- and 5- connections. The right side of R4 should also be connected to ground, and 24 kΩ would set the current limit of the IC to 2A (page 7). On pin three is one of the mistakes in your schematic as far as I can tell, I think that pin is really connected to the point between R6 and R5, for output voltage feedback. I also think R6 is meant to read “84D”, which would be the resistor code for 732 kΩ with 1% tolerance. If you calculate the output voltage of the regulator with the 0.6V feedback voltage from the datasheet and 732k/100k resistors, it comes out to 4.99V, which would be compatible with the USB 5+/5- stuff. Connecting EN to VCC (pin 4 to 5) is also common to permanently enable an IC, but I think there’s another error in your schematic: I’m pretty sure those two pins are directly connected to BAT+ instead of through C4, and that C4 instead connects from those two pins to ground to stabilize the input voltage.

Edit: Would you post of link to the product on AliExpress? I’m interested now :D

There’s no way U1 is charging the battery. How would it? If the connection labeled USB is the power source, it’s only connection to U1 is through a 100k resistor and a reverse biased diode. Also, charging AA batteries? Sure, you could plug in some NiMH cells, but then the device would need to have explicit instructions telling you that this is indeed a charger and to only ever insert rechargable AA battery cells.

If you desolder U1, you should drop about 0.5V of your battery voltage across D1 and maybe the remaining 2.5V will be enough for the other components to do something, but I doubt they will be very effective in whatever their purpose is.

Feels an awful lot like a step-up converter. I’m missing the ground connection though and potentially a connection to a voltage divider for feedback. Where does R4 lead to? Are you sure there is no connection from the middle right pin except to C3? Is pin 1 of U1 marked? Can you make a detailed photo of the IC to better identify the text on it?

Nothing exciting. als commented that he likes some FUTO software, among other things because it’s Open Source, and I responded that it is not.

I meant the definition by the Open Source Initiative, but in almost all cases, it doesn’t make a difference if you use that or the FSF definition.

The license shall not restrict any party from selling […] the software

it may not restrict the program from being used in a business

In addition to the restrictions on commercial use, the FUTO license says that you may not remove payment logic and then share your modified version, which might also be unacceptable for the FSF and/or OSI.

It is not Open Source, it is “Source Available”. The Open Source definition requires that users get certain rights that the FUTO license does not grant.

I can’t say anything in regard to modern printers, but I don’t trust any proprietary device connected to the internet. I have an old inkjet and an old laser printer, both without network functionality themselves - but I connected them via USB to a Raspberry Pi, which runs a printer server and makes them available on the local network. I can print and scan from my Linux laptop, and I also managed to print something from my Android phone. Haven’t tried Windows yet. Configuration of the Raspberry Pi was easy, especially enabling scanning via the network.

We used Jitsi quite a bit during Covid, I was very happy with it, and I don’t remember any complaints from other people.

https://umap.openstreetmap.de/en/

There are other fast charging standards than Power Delivery. USB Battery Charging defines that when the data lines are shorted, a device can draw more current (up to 1.5A), but still at 5V. QuickCharge on the other hand uses the data lines to negotiate higher voltages, so an A-to-C cable can’t protect you from that.

For Power Delivery, higher voltages are negotiated using the CC (configuration channel) pins. If you use an A-to-C cable, the A side does not have the CC pins and therefore you can’t get more than 5V.

Have you checked what voltage arrives on the board if you use a regular USB-C charger? Maybe the headphones negotiate and need a higher voltage than 5V. Does it charge with only 5V supplied? (could be forced by using an A-to-C cable in case of Power Delivery)

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