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Which is this SMD IC

sudhir.khamari@gmail.com

I am trying to repair a Jack Martin JM Trolley z12 sound box. The sound box works fine on AC, only the battery in the box is dead; when I opened the box found that the Power coming to the battery terminal is 3-5 volts, where as the battery itself is 12v. So I doubted something bad happened in the circuit. The circuit has a burnt 8pin smd ic which had "R56" printed on it. I am not able to find any detail regarding the IC.

 

     I have attached a picture of the circuit with marked 1> The IC that is burnt, 2> 12v DC input jack, 3> Connector to the 12v Battery.

 

Any help will be really appreciated. Thanks in advance.

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  • 0

    The chip doesn't look burnt to me. If you are referring to the silk screen, R56 probably refers to a resistor near the chip.

    If you want to know what the chip does, you can try mapping the schematic using continuity measurements between all components.

    Presumably the circuit should be charging the battery when AC is connected. If the battery is 12V there should be at least 12V coming to the battery terminals.

    However, if there is no battery present, it may detect it and do something different.

    The circuit needs to decide whether to run off battery or AC. You need to map out which components are involved in this decision. Often both the battery and the AC supply feed the same point through diodes and there is a separate circuit to trickle charge the battery. It is also possible the AC is detected and turns off the battery. If something is messed up in that detector, the battery could be always off.

    If a 12V battery is connected and the circuit does not run off it, it may mean that there is a bad connection between the terminals and the power supply.

    There won't be many components in this path to check, it could be just a PCB trace or it could be a diode or possibly a transistor. Follow the copper from the terminals and see where it goes.

  • 0 in reply to dougw

    Thanks Douglas,

       The chip's one leg was dark and very small portion of the chip just above the leg has burnt and turned into dust. Thats why I doubt it is burnt.

     

    You are right that there is a resistor near the chip which is labelled as r56 on the PCB. Also the chip had R56 marked on it, it got erased when I rubbed it with finger.

     

    I checked the power coming to the battery terminal when AC is connected and with the battery disconnected. Will check again with the battery connected.

     

    Thanks,

    -Sudhir

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  • 0 in reply to dougw

    Thanks Douglas,

       The chip's one leg was dark and very small portion of the chip just above the leg has burnt and turned into dust. Thats why I doubt it is burnt.

     

    You are right that there is a resistor near the chip which is labelled as r56 on the PCB. Also the chip had R56 marked on it, it got erased when I rubbed it with finger.

     

    I checked the power coming to the battery terminal when AC is connected and with the battery disconnected. Will check again with the battery connected.

     

    Thanks,

    -Sudhir

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