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Help with replacing component on circuit board

Discussion in 'Troubleshooting and Repair' started by marcus_clarkus, Jul 25, 2013.

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  1. marcus_clarkus

    marcus_clarkus

    5
    1
    Jul 25, 2013
    Product: Polk Audio PSW202 powered home theatre subwoofer
    Problem: Blows fuses in matter of seconds
    Solution: Found component causing internal short, need advice on replacing it

    burnt Audio IC amp-
    [​IMG]
    [​IMG]
    [​IMG]
    I'm fairly sure that the darkened solder on the bottom of the board has not come into contact with anything it shouldn't have.

    amp without aluminum cover-
    [​IMG]

    Picture of everything (aluminum cover in place)-
    [​IMG]

    So the little audio amp on the circuit board burned out and I need to replace it with this:
    Audio IC (mouser electronics)
    Question #1: I've soldered wires before, is there anything special I need to know about soldering a circuit board?

    Also, the heat sink for the amp was in contact with a large, aluminum enclosure and had some thermal paste and a plastic insulator on it.

    aluminum cover, note the plastic piece held in place on it with thermal paste-
    [​IMG]

    Question #2: Can I clean the surfaces (as I would on a PC's CPU) and reapply thermal paste that is meant for a PC's CPU?


    Thanks in advance for any answers/advice!
     
    Last edited: Jul 25, 2013
  2. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    If you are sure that the amplifier is faulty, then the best way of removing it is to snip the leads with a side cutter and remove each wire separately. Use a solder sucker to get rid of most of the solder and braid to remove the rest.

    The heat sink paste does not glue surfaces together, the components should be mechanically clamped to the heat sinks. They may be electrically connected to the heat sink or may be insulated. Make sure you replace as found. The heat sink compound should cover as much area as possible and should be as thin as possible. It is there to conduct the heat and is not very good at it but is much better than air. Fix to the heat sink before soldering the new amplifier as it can be difficult to change the position if you get it wrong.

    A lamp in series with the input power can limit the current and stop fuses blowing. Once the amplifier is working then it can be directly connected to the mains.
     
    Last edited by a moderator: Jul 25, 2013
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Excellent answer duke37!
     
  4. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    ohhh its definitely faulty ... look at the huge hole blown in the top of it in pic 1

    Dave
     
  5. marcus_clarkus

    marcus_clarkus

    5
    1
    Jul 25, 2013
    thanks for the input guys. And duke, that's a really good idea to attach the IC to the heatsink before soldering it to the board, I'm sure you just saved me a lot of frustration and time
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    It's not just a good idea for that reason. It minimises force on the soldered connections to the device pins. This is a very good idea, since pins on hot components are already prone to dry joints. So it's also best for long term reliability.
     
  7. marcus_clarkus

    marcus_clarkus

    5
    1
    Jul 25, 2013
    I got it working, thanks for all your help!
     
  8. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    Excellent, glad to know that you have been succesful.

    I have a Sony audio system here which had an argument with a thunderstorm and the amplifiers have blown apart. Will have to get a round tuit !
     
  9. elebish

    elebish

    177
    12
    Aug 16, 2013
    Good advice Duke! Ed.
     
  10. marcus_clarkus

    marcus_clarkus

    5
    1
    Jul 25, 2013
    3.5 year update: subwoofer still works great after my fix. thanks again duke!
     
    Last edited by a moderator: Feb 5, 2018
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    If you're coming here from the polkaudio forum with a different question about this subwoofer, please don't post in this thread.

    If your subwoofer is "coughing", then this might be the thread for you.
     
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