Dead subwoofer

Discussion in 'The Projects Forum' started by Edmunds, Jun 30, 2014.

  1. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    Friends,

    Some 6 months ago my Boston active subwoofer died in me with a flash. It blew a fuse and I was brave or stupid or both enogh to short the circuit braker to see what's going on. No chances with mains power taken though, all safety obeyed. The guilty thing turned up quckly, burning one of the PCB tracks to mid terminal of MDF11N60 MOSFET on one of the boards that cannot be anything else than one of the power supplies.

    Now I finally have some discressionary energy to look at the thing.

    Clearly, the evidence shows, the MOSFET is to blame. At least for the first instance. It is not difficult to replace, but as I'm waiting for the thing to arrive, I'm wondering if a blown MOSFET is a typical thing to happen and if I should look further for the reason for this.

    Sorry not to have any schematics or visuals to provide. Any reactions appreciated. Thank you,

    /Edmunds
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,429
    3,360
    You want to avoid blowing other things, especially the subwoofer.

    What you need to do is to take static voltage measurements without the subwoofer attached.

    Next, you can take static voltage measurements using a resistive load.

    If everything checks out ok, you can put an incandescent 12V automotive bulb in series with the speaker as a precaution.
     
  3. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    MrChips, thank you for your reply. What do you mean with static measurements?

    My local shop did carry a "suitable replacement" according to them - P10NK60ZFP. I checked the datasheet and the basic parameters seem to be within reasonable range. The internal picture does not look that well, but what the heck, I thought. And soldered the thing in. Now that was a real flash :). Visual inspection suggests that now the transistors are fine but a small IC on some kind of small add-on board caught fire. I cannot even read what the chip was now. Pictures attached. I'm lost, but ready to continue trying as the other way for the thing to go is trash directly :).

    Edmunds
     
    Last edited: Jul 1, 2014
  4. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    One more pic.
     
  5. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    And one more.
     
  6. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
  7. Experimentonomen

    Member

    Feb 16, 2011
    331
    46
    Don't bother trying to repair the current power supply, its simply not worth the money in replacement parts.

    Boston is like the cheapest of the cheap, attemting to repair this one will end up costing as much as just buying a new one.

    Also you do not need any subwoofer as your main speakers(assuming a 6" or larger woofer) will handle the lows just fine.


    "But i want that kick in my chest!!" NO! Just NO, grow up...
     
  8. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    Thank's, but that is not the case. My set is of smallish square speakers definitely less than 6". On top of that, I'm trying to learn something in the process. Even if I end up throwing the thing out in the end, hopefully I will understand some more electronics. And it is not that bad to my liking, but that is a matter of taste and ambition for simple home cinema system, I guess :).

    Edmunds
     
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