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Yamaha Portable Grand DGX-220

Discussion in 'Repairing Electronics' started by pedals, Oct 20, 2012.

  1. pedals

    pedals New Member

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    The Bb2 key on my Yamaha keyboard is faulty and makes it very difficult to play.When pressed it sounds at full volume regardless of how hard it is struck. I have cleaned the key contacts using Isopropyl Alcohol on a cotton bud to no avail. (I also have a Roland synth which sometimes does the same thing and this method cures it). Is there a component in the touch sensitive circuit that needs replacing ?. Any advice would be welcome. There are no service facilities handy to where I live. Regards..................Pedals
     
  2. unclejed613

    unclejed613 Well-Known Member

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    Yamaha uses a pair of contacts to sense the speed which the key is pressed... one contact cone is shorter, introducing a slight delay. the delay time indicates how hard you are hitting the key. you need to clean both sets of contacts and the carbon buttons in the rubber contact strip. it's the carbon buttons that pick up debris on their surfaces that usually cause problems with the switches.
     
  3. Mr RB

    Mr RB Well-Known Member

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    If one contact is reading as "on" it will read a zero time for the key acceleration(re what unclejed said).

    Maybe cleaning will fix it, otherwise it could be a damaged input component.
     
  4. dave

    Dave New Member

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  5. pedals

    pedals New Member

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    Thanks unclejed. I did clean both contacts as well as the carbon buttons but I'll repeat the process more thoroughly now in light of your reply.
     
  6. pedals

    pedals New Member

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    Thanks Mr RB. I'm going to try giving the contacts a more thorough clean. If this doesn't work do you know how I could determine which component could be at fault ?.
     
  7. Mr RB

    Mr RB Well-Known Member

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    That may not be easy! :)

    First the cleaning, you can use a multimeter set to the megaohms range to check the contacts, normally if there is a spill or corrosion issue that contact will measure lower ohms than the other (good) contacts around it.

    Sometimes cleaning just spreads the contaminant, so you need to clean multiple times with new cloth each time. I use like a soft t-shirt type cloth and just damp with metho (alcohol) and like I said a few times and an few pieces of cloth. Don't use a lot of force or scrubbing as the contacts are often a conductive paint material.

    If you've cleaned it well and tested with the ohmmeter and it still has the fault, then it's probably time to get a service manual and start tracing the signal from the contacts to the electronics.
     
  8. pedals

    pedals New Member

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    I did reply to your last post Mr RB but it doesn't seem to have registered. Thanks for the further info, I'll do as you suggest when I get a chance to work on the keyboard again....Cheers.
     

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