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!

  • jeinzi@discuss.tchncs.deEnglish
    4·
    9 days ago

    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?

    • bruce965@lemmy.mlOPEnglish
      3·
      9 days ago

      Yeah these pictures are not the best, are they? 😬 I took some more, they might be a tiny bit clearer, but I’m afraid that’s the best I can do with my camera, link to pictures. Seems to be AL322 or maybe AL022? Neither of the two returns any results for me, though.

      R4 leads to somewhere for sure, but it’s hidden below the IC, so I can’t follow it. To disasemble it any further I would need to break it entirely. I guess that’s an option. I checked the middle right pin again, it only seems to go to C3 as far as I can tell. Pin 1 of U1 doesn’t seem to be marked, at least not anymore, but perhaps it might be guessable from the direction of the text?

      • jeinzi@discuss.tchncs.deEnglish
        3·
        8 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·
          8 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

  • partial_accumen@lemmy.worldEnglish
    4·
    9 days ago

    The photo isn’t great, but it looks like a 6-pin package. From your schematic I would assume its part of the battery charging circuit.

    You say it “blew” is it shorted or open? If open, then my guess is the rest of the device should function, you just won’t be able to charge the battery. If its shorted, I could see that draining any current away from your piezo driver.

    For component identification, have you tried an image search of your board (with a better picture with more light)?

    • bruce965@lemmy.mlOPEnglish
      2·
      9 days ago

      Sorry about the pictures, that’s the best I could do with my phone camera. I took some more, they are not much clearer, but there are more angles at least, link to pictures. It certainly is a 6-pin package.

      It didn’t occur to me that it could be part of the battery charging circuit, that would be nice as honestly I don’t care about using it as a battery charger (it takes two AA). I am a bit worried about plugging batteries again, as I am afraid I might damage it further. Assuming pins on the left to be 1, 2, 3 from the top and pins on the right to be 4, 5, 6 from the bottom: pin 1, 2, 5 and 6 seem to be shorted, pins 3 and 4 give me 90k resistance.

      I didn’t try image search, do you mean on Google Image Search?

      • partial_accumen@lemmy.worldEnglish
        4·
        9 days ago

        It didn’t occur to me that it could be part of the battery charging circuit, that would be nice as honestly I don’t care about using it as a battery charger (it takes two AA).

        I’m a bit confused. Two AA batteries usually means 3v DC which is common to power a device. However, in your schematic on the left hand side, you have a symbol that represents a battery, its labeled 5v, and USB. I assumed this was the power source for the device. If not, why does your device have two power sources and one is not rechargeable.

        I didn’t try image search, do you mean on Google Image Search?

        yes

        • bruce965@lemmy.mlOPEnglish
          3·
          9 days ago

          If not, why does your device have two power sources and one is not rechargeable.

          That’s a good question, and that’s also something else I didn’t think about. I just checked the instructions and it’s not clear. Perhaps it’s an alternative way to power it. I’ll be honest, this is a cheap device. I don’t want to fix it because it’s expensive, I want to fix it because I literally didn’t turn it on even once before blowing.

          I drew it as a battery, but that’s actually USB power (5V). That was probably a poor choice from me.

          try image search

          Oh. My. God! It worked! How on earth could it know that this specific PCB is what it is? That’s black magic! It didn’t find this specific one, but it correctly classified it and it also found similar designs. Seems like that blown component actually is part of the charging circuit, since other similar designs seem to omit it. I’ll try desoldering it and see if the rest still works. Thank you very much for this suggestion, that blew my mind!

      • jeinzi@discuss.tchncs.deEnglish
        2·
        8 days ago

        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.

        • bruce965@lemmy.mlOPEnglish
          2·
          8 days ago

          Fair point. There were no such instructions.

          I tried desoldering U1, disconnecting the piezo, and powering it with 3V from the batteries side. It blinks rhythmically, so I assume the MCU (or ASIC) is fine. But if I connect the piezo, power consumption drops to < 1mA and nothing else happens. So yeah, that component’s purpose is probably not to charge the batteries.

          I will try to read the markings again with a magnifying glass later today. Unless you or someone else have better suggestions.