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Yamaha YPT-300: No b-flat; e-natural anywhere!

Discussion in 'Troubleshooting and Repair' started by Tuesday Dog, Feb 19, 2011.

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  1. Tuesday Dog

    Tuesday Dog

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    Feb 19, 2011
    I'm working on a Yamaha YPT-300 electronic keyboard which I found. I completely disasembled the unit, cleaning everything (they keyboard assembly has been completely cleaned and remounted). I discovered that the b-flat and e-natural keys do not sound in any octave across the board.

    The sample tune plays all keys, so I am thinking that the fault is not in the on-board chip. I have no working schematic diagram.

    I am wondering if this rings any bells with anyone (perhaps minus the b-flat and e-natural ones) ?

    I found this unit junked, I know it could be completely replaced cheaply, but it would be nice to straighten it out.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Are the keys multiplexed?

    That may point to a single row or column that's not working. And that may directly point at a fairly small range of components.
     
  3. Tuesday Dog

    Tuesday Dog

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    Feb 19, 2011
    Polyphonic

    I think you are asking if the keyboard is polyphonic, which it is.
    It has 61 keys, and yes, you can play chords and multiple keys at once.
    For me, a person that has been repairing without schematics for most of my life, it is a slightly intriguing chance to see how these keyboards are designed.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No, not exactly. What I'm wondering is, "Is one side of the keyboard switches common for sets of keys, so perhaps each octave of keys has one side of the switch in common, and the same for the next octave, etc, but these common connections are distinct for each octave?"

    If so, there may be a common part of the circuit for handling each b flat and e natural.

    I wouldn't have thought that multiplexed keyboards were the norm, but it would explain the common fault.

    On the other hand, there may be something common to each note in each octave (maybe something to do with a frequency divider?).

    You need to look at things common to these notes, because it would be too much of a coincidence otherwise.
     
  5. MattyMatt

    MattyMatt

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    Mar 24, 2011
    Most of the time, kids toys have multiplexed keyboards (especially the really cheap ones), this one probably doesn't, but I would defiantly lean more towards the frequency divider or some sort of crystal they all share in common (like steve was saying).
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Interestingly enough, I just repaired a keyboard and it had multiplexed keys And it wasn't a toy either!

    The full 84 keys with the ability to detect how fast you were pressing each key was transferred by 2 cables each about 16 way.
     
  7. MattyMatt

    MattyMatt

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    Mar 24, 2011
    That's rather nifty! Then again, I've only had a few really nice keyboards apart.
     
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