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Keyboard no sound

Discussion in 'Troubleshooting and Repair' started by Tha fios agaibh, Apr 13, 2017.

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  1. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    My daughter is bummed out that her Huntington KB54 keyboard died.
    Powers up, display responds to functions but has no sound at all.
    I found power 12vdc power supply failed and was outputting 24v (unloaded)
    I replaced with new ps and opened it up and and verified 12vdc at amp board and 5vdc rail past lm7805 regulator.

    In demo mode that plays music, I tried a fat finger technique over back of circuit board to try and introduce noise but no sound at all from speakers.

    Yellow wires from synthesizer chip read seemingly constant 2mv ac on my dvm.
    Seems low.

    I plan on checking headphone jack.

    If the overvoaltage was the problem that lead to failure, where should I start to look? Electrolytic caps?
    Do you know a resource where a schematic could be found?
     
    Last edited: Apr 13, 2017
  2. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    20170413_123029.jpg
     
  3. Bluejets

    Bluejets

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    Oct 5, 2014
    I saw a video on one of these and it showed schematics on the last page of the included manual.
    Too blurry to see anything though. Almost at the end of the video.
    Just thought you might be able to chase up an owner manual.
     
    Tha fios agaibh likes this.
  4. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Thanks, I might get lucky and be able to download a user manual.
    Usually a user manual doesn't include schematic.
     
  5. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    1492206319991.jpg I don't see how power gets past D1(1n4007) when cathode is hooked to positive pin of power jack?
    I'd expect it the other way around.
    What am I overlooking?
     
  6. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Screenshot_2017-04-14-16-54-30-1.png The top tracer is negative. Below that positive node that cathode connects and nothing else as far as I can tell.
    Below that anode lands.
     
  7. Tha fios agaibh

    Tha fios agaibh

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    699
    Aug 11, 2014
    oops, I mistakenly put red wires in wrong place. Power gets past by power switch wire.

    I believe I've got a failed amp ka2206 from over voltage since it runs on full 12dc.
    Data sheet says it's absolute maximum is 15v and old ps was outputting 24.
     
  8. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Update:
    I replaced the ka2206 and everything works.
    My daughter will be thrilled to get it back and return to her "music"
     
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