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CreativeLabs L3800 2.1 sound system works fine for 20 minutes

Discussion in 'Audio' started by alex ezorsky-lie, Jun 22, 2018.

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  1. alex ezorsky-lie

    alex ezorsky-lie

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    Aug 27, 2015
    And then the treble cuts out, nothing but bass.

    Then randomly it comes back for 5 seconds to 5 minutes then this on and off gets more off then on until maybe an hour or so when its just bass forever.

    I've searched everywhere for loose connections bad caps etc. I've tried tapping, poking spinning twisting bending every little piece and wire I could find and it seems nothing I do correlates with the treble coming in and out. And yes I've tried multiple sound sources.

    The system has a power supply board in the subwoofer as well as a separate sound-control / headphone-input unit wired to it. The control unit has 2 buttons for power/mute as well as a push/turn knob for volume/bass control (no treble control). With headphones plugged in the sound is always fine, which leads me to assume it's something with the power supply?

    What part of a fairly simple circuit board (power supply) or relatively simple sound control board would become faulty over fairly reliable period of time like 20-minutes? My guess would be a transistor or any parts with heatsinks but they all look fine. Guess I should learn to properly test those transistors.

    Just hoping someone has a useful guess.

    Thanks!
     
  2. dave9

    dave9

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    211
    Mar 5, 2017
    It is possible you could have transistors leaking as they heat up, but I would wonder if it even has any discrete transistors in it, or just chipamp ICs? It might help if you can find a schematic. It seems to be a bi-amped design so it is possible the amp stage for bass could keep working while it stops for treble, but since bass does work, and seemingly an opamp at least as buffer would indicate a lower voltage power rail is also working if present at all, so I am doubting the power supply has a problem, but you certainly could measure it with a multimeter.

    Otherwise, another common reason for this kind of behavior is a bad solder joint. I would examine them all under a strong light and magnifying glass and touch up any that are questionable with a soldering iron.
     
  3. 73's de Edd

    73's de Edd

    2,805
    1,176
    Aug 21, 2015
    Bass always works but after the 20 mins the satellite / treble and midrange remoted speakers drop out ?

    Get a fan, set on high, and get it in as close as possible to the circuitry and direct onto the electronics and see if the cooling then gives unlimited run time . . . as compared to the prior 20 mins.

    Then if this is so, it then means the tracking down of the heat sensitive aspect of parts.
     
  4. alex ezorsky-lie

    alex ezorsky-lie

    24
    0
    Aug 27, 2015
    Thanks folks!

    So I couldn't track down the heat related issue, but I noticed that power supply heated up to pretty warm so I tried a new one from ebay and that seemed to help. But then I plugged in my headphones and here's another weirdness, the bass speaker was the only thing that DIDN'T cut out when I plugged them in (It's all supposed to cut out).

    So it seems there is something on this board that is very confused/worn about bass/treble on/off.
     
  5. dave9

    dave9

    864
    211
    Mar 5, 2017
    ^ I wonder if there is a switch built into the headphone jack, or added onto the end of it so when the tip of the plug is inserted it switches, and that switch is faulty.
     
  6. KJ6EAD

    KJ6EAD

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    157
    Aug 13, 2011
    Many modern integrated components have thermal protection capability built in to their design such that once a temperature threshold is exceeded, the device turns off its output until it has cooled to below a reset setpoint. In practical use where an overload condition exists, this leads to thermal cycling where the first shutdown takes relatively longer to occur as ambient thermal masses act as heat sinks. Once these masses have been preheated, the next shutdown occurs more quickly and so on until equilibrium is reached. This is what Edd was referring to above where he suggested the use of forced air cooling as a diagnostic tool. Correct me if I'm wrong @73's de Edd.

    If cooling significantly improves performance then you have an overload condition (likely) or a faulty component and/or heat sinking (less likely). A thermal camera is a good tool for finding the problem area but the damp finger test is a well-worn old school method.
     
  7. alex ezorsky-lie

    alex ezorsky-lie

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    0
    Aug 27, 2015
    Thank you folks so much for your time and expert insights. Also yes @dave9 I checked the headphone jack input detection switch for faults and found none.

    I think I will have to offer it up on craigslist for free to the next best hobbyist but thanks for the help!
     
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