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Rockin Santa Christmas Doll

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  • Rockin Santa Christmas Doll

    Hi everyone, I am trying to fix a toy for my mother in law that is very special to her. it worked fine until this year when she took it out of the box and now the music wont play. the body still dances. when you turn it on all the speaker will do is hum at a steady volume wether you increase or decrease the volume knob. here is a link to what it is supposed to do; https://www.youtube.com/watch?v=EmuvfJfrmiA .
    It has a very simple board inside its foot with only 20 components on it. I have inspected it thoroughly and there is not anything that is obviously bad. one of the resistors was measuring out of tolerance so I removed it to test again and it is good after all. I have limited understanding of these components and have been searching for a while now for what may be the cause of the buzzing. She told me that she could hear the music very faint under the buzzing sound but i couldn't hear it.
    In my research I came across information that a capacitor that is partially bad can cause the buzzing. Can anyone confirm that please? All the capacitors appear healthy and any helpful thoughts are welcome.

  • #2
    So the thing sticking out the board is going to be the microcontroller, that's the only part you can't replace. First thing I'd do is check all solder joints, things like this are mass produced so seeing bad soldering is pretty common place. The buzzer itself is most probably going to be fine. What do die just sitting there doing nothing is electrolytic capacitors, especially if it's been in a damp loft etc. If you have an ecr meter you can check all of those. If not they are literally cence / pence off mouser etc so I'd just replace the lot. If that doesn't solve it I'd replace all the transistors too as that's the next most likely thing to go wrong. You can test the transistors if you have a meter that is capable of testing them or if you really want to get creative you can knock up a test circuit on bread board. Personally I'd just eBay the transistor part number or get from mouser.
    you can test all the components but it depends if you have the equipment or not, otherwise it's cheaper just to replace the components. Iv fixed multiple pc power supplies just by changing all the caps. It's not like an iPhone where there are hundreds.

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    • #3
      Thats your transistors https://alltransistors.com/pdfview.p....pdf&dire=_utc

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      • #4
        By the look of the photo the capacitors you have are :
        2x
        16v 47uf

        1x
        50v 0.22uf

        The rating etc is written on the sides of them.

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        • BigN8
          BigN8 commented
          Editing a comment
          Thank you crea2k. that is very helpful. i was just about to tear the rest of it apart and look at the speaker but I will replace the 3 caps first and see what happens.
          Update: I just ordered the replacement caps and transistors and should be here before christmas. Ill update again with the results
          Last edited by BigN8; 12-14-2017, 12:52 AM.

      • #5
        If you've not looked at the speaker I'd at least check it or desolder the wires from the board, cut up an old set of headphones / ear buds and wire one side to the speaker. That will test that. If you can get to it though it's far easier just to visually check the solder joints on it than create a test rig for it.

        only replace one bit at and time and then test. Pay attention to the capacitor polarity as they are polorised unlike Iphone etc caps so the stripe down the side has to go to negative or you'll blow it up.

        if you replace the transistors make sure they face the correct way too.

        my bet is on the capacitors though as they'll be some cheap Chinese garbage. I replace them on HP pc power supplies and saved £80 for new psu so I dread to think what caps they put in those toys.

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