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!

  • bruce965@lemmy.ml
    OPEnglish
    2·
    20 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·
      20 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.ml
        OPEnglish
        3·
        20 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·
      19 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.ml
        OPEnglish
        2·
        19 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.