Wierd keyboard problem

Discussion in 'Electronics Repair' started by Brightsbane, May 15, 2011.

  1. Brightsbane

    Brightsbane

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    May 15, 2011
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    Sorry that my first post is a help question but I couldn't find any specific information anywhere else.

    I have an old electronic keyboard/synthesiser - Technics KN500 circa 1994 - which when played loudly, cuts power and the unit turns off. The keys are touch sensitive so the harder you press the louder the note.

    It usually takes playing a big chord quite loudly for the unit to switch off. If I turn the master volume down then I can bang on it as much as I want and it stays on. Every other function of the unit works normally.

    I have medium level of electronics knowledge and after opening the unit I couldn't see any obvious compent problems.

    If I had a better idea of what might be causing the issue (ie. what type of componentry regulates the master volume) I might be able to narrow it down.

    Thanks for reading.
    Brightsbane, May 15, 2011
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  2. Brightsbane

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Location:
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    Does the unit turn off immediately the loud sound is played? Or does it take a period of loud playing?

    Describe the "tuning off" -- does it appear totally like the power is off (including any power lights) or is is simply mute?

    Are there any heatsinks inside? Do they get warm or hot? and do the transistors connected to them seem distinctly hotter than the heatsinks?

    Is the sound distorted, especially just prior to the unit turning itself off?
    (*steve*), May 16, 2011
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  3. Brightsbane

    Brightsbane

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    Hi steve,
    All power to the unit is lost as soon as a loud chord is played. Its been a while since I've had it open so I'm not sure about the heat sink or trannies. I'll open it up tonight and have a look. I probably should have stated the power supply rating etc so I'll get that too.
    Thanks.
    Brightsbane, May 16, 2011
    #3
  4. Brightsbane

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Location:
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    If it switches off very quickly, then it's less likely that something is heating up.

    It could be that the power supply shuts down when overloaded.

    If the latter proposition is true, then either something is drawing too much current, or the overload detection has a fault (and is triggering on too low a current)
    (*steve*), May 16, 2011
    #4
  5. Brightsbane

    MattyMatt VIP Member

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    A quick question, when you are playing this loud chord, are you doing this while its on batteries or an external power supply (wall wart?).

    I'm thinking if it is a wall wart, its possible the problem may lie in that as well... just a quick thought.
    MattyMatt, May 17, 2011
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  6. Brightsbane

    Brightsbane

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    The issue happens when connected to mains power (240V in Australia), when connected to a 12 V source or even when only running on batteries.

    Steve, I think an overload detection fault is sounding quite likely. I'm not too sure how I would diagnose that but I'll start researching.

    Thanks.
    Brightsbane, May 18, 2011
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