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Salvaging Logitech speaker system

Discussion in 'Electronic Repair' started by Mike S., Oct 1, 2005.

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  1. Mike S.

    Mike S. Guest

    I have a dead Logitech Z-680 5.1 computer speaker system that I was
    wondering about doing salvage work on, before discarding.

    It consists of a subwoofer with all the amp circuitry and connectors for
    the main speakers on the back, and a dedicated control pod that connects
    to it using a custom wired DB9 connector.

    The system stopped working and, since it was under warranty (and
    discontinued), Logitech simply replaced the entire thing with the current
    model (Z-5500) and does not want any of the old equipment returned. The
    old and new systems are electrically incompatible, so I just boxed the
    Z-680 setup and am triyng to decide what to do with it.

    The electronics pod, which contains the controls, analog/digital inputs,
    Dolby/dts decoders, and preamp, powers up and detects and processes input
    signals appropriately. There is a power-on "thump" in all speakers when
    you fire the thing up, and the sobwoofer still has a little buzz coming
    out of it (that was normal), but after that ... nothing. Audio goes in,
    but not out. There is a special test mode that sends tones to all speakers
    for setting levels ... I hear nothing.

    I'm not sure if the failure is in the pod or the main (audio) unit on the
    subwoofer, though I suspect the former. I opened the pod ... lots of
    surface mount chips, no visible fuses or resettable devices. Not
    user-serviceable.

    The subwoofer has this huge metal cage bolted on the back which contains
    the audio amplifier circuits. I'm pretty sure the DB9 input on the back
    contains the 6-channel preamp output from the control pod. I was thinking
    of trying to send some test signals into the subwoofer's input socket, 2
    pins at a time, until I figure out whether any of them elicit audio output
    from the speakers. Perhaps I can salvage the subwoofer and simply hook a
    line-level audio cable to whichever of the two DB-9 pins gives the desired
    effect.

    Comments/suggestions? Thanks.
     
  2. James Sweet

    James Sweet Guest

    I suspect the problem is something simple, cracked solder joint at a
    connector, this might be a good opportunity to practice repair as a speaker
    system is relatively simple and safe to work on.
     
  3. mike

    mike Guest

    Most of the busted speakers I've seen had mechanical problems.
    Banged the volume control and broke it.
    Banged the signal conector and broke it.
    Dropped and cracked the circuit board.
    You need either an oscilloscope or a signal injector.
    mike

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  4. James Sweet

    James Sweet Guest

    I don't think I've ever used either to repair speakers, usually the problem
    is pretty apparent once you get it apart. A walkman is useful for supplying
    a signal though, a DMM is usually sufficient for tracing.
     
  5. Mike Berger

    Mike Berger Guest

    A Walkman makes a fine audio signal injector, but it's pretty
    delicate and expensive,and has limited output.
     
  6. jakdedert

    jakdedert Guest

    A *finger* is often enough to supply signal (although the walkman is
    higher-level, more stable approach). Touch an input and listen for hum.
    Another (working) powered speaker is useful as a signal tracer
    (protect the input with a small capacitor).

    A DMM 'good enough' for the above can be had for $10 or less, and will
    come in handy in many other situations.

    jak
     
  7. jakdedert

    jakdedert Guest

    If you're testing *unpowered* speakers, yes. Otherwise, the output is
    entirely adequate. Shuffle down to your local pawn shop or even thrift
    store, and pick up a walkman for less than $5...not expensive at
    all...or particularly delicate for that matter.

    But if you're concerned re: the above, buy a signal generator (not less
    expensive)...or a $1 (Dollar Tree store stock) FM radio.

    jak
     
  8. Mike S.

    Mike S. Guest

    Thanks, I think that might be the safest initial move. Remembering that
    one of the pins also supplies POWER to the control pod, I figured I'd test
    things out with a DMM first, and cross off any pins that have voltage
    coming out of them.

    I've looked around and Logitech seems to have refused previous requests
    for pinouts of the input connector; though some have disassembled the
    subwoofer to fix internal rattles, nobody has bothered to map the input
    port. Opening this thing is such a bear that, given the choice, I'd throw
    it out rather than invest that much time if poking around from the outside
    doesn't yield anything.

    Thanks for the ideas, folks.
     
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