Hi! I recently purchased a nice gadget from AliExpress, this should be the circuit to drive an ultrasonic piezo. Silly me, I put the batteries backwards and the U1 component on the bottom left blew up.

I know a bit about circuits so I reverse engineered it (there might be mistakes), but I am not skilled enough to identify the component in order to look for a replacement. Can someone help me identify it? I can read ___22 on it.

Here’s another version of the schematic, which might be easier to understand.

Schematic

Thank you for your help!

EDIT: I couldn’t identify the component, but I did a Google Image Search as suggested by @partial_accumen@lemmy.world and it found similar PCB designs. It very much looks like this component is part of the charging circuit, which I do not particularly care about. I will try desoldering it and see if the rest of the device still works. I will post the outcome here.

EDIT 2: with a lot of help from @jeinzi@discuss.tchncs.de I managed to fully reverse engineer it and fix most of the mistakes in the schematic. That component was just an FP6291 after all, part of a circuit to step up the 3V from two AA batteries to 5V required by the MCU. I replaced that whole section with a step up module I had previously purchased from AliExpress, and now everything works again.

Here’s the final (mostly accurate, hopefully) revision of the schematic.

Schematic Revision
(link)

Lessons learned:

  • Always double-check battery polarity
  • In the age of AI, Google Image Search can now help identity circuits
  • Sometimes a circuit that looks complex can actually be much simpler in the end
  • AskElectronics@discuss.tchncs.de amazing community on Lemmy

That was fun! Thank you very much to everyone who contributed to this thread!

  • jeinziEnglish
    3·
    9 days ago

    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

    • bruce965@lemmy.mlOPEnglish
      1·
      9 days ago

      You must have spent a lot of time into this, thank you so very much 🙏

      With a bit of persuasion I managed to disassemble it without breaking it. I desoldered U1 and I can confirm that pin 2 is GND. Also, here are better pictures taken with a magnifying glass. Note that pin 1 and 3 were shorted to pin 2, but it didn’t make sense to me, so I assumed they bridged due to the thermal shock when the component burned, so I scraped around them.

      And here’s a link to AliExpress.

      I guess there is no easy way to bypass it then, it would probably cheaper to buy a new device than to buy a replacement IC. Also, I guess now I will have to upload a clean version of the corrected schematic, I owe this to you and the other great people that replied.

      EDIT: I could probably bypass it entirely, I just need to inject 5V. Here’s the updated schematic.

      Schematic