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Yamaha E-70 issues, cross triggering notes

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  • Yamaha E-70 issues, cross triggering notes

    I just obtained a seemingly mint E-70 last week from a Hammond repair guy. Somehow during transport something was adjusted so that when I play a D or a C# one triggers the other as well and you hear both notes. This only happens with D and C# and it happens on all of them, both sets of keys. Is there somewhere I can start looking so I don't have to pay for repairs or have to lug 350lbs. to a shop?

  • #2
    Re: Yamaha E-70 issues, cross triggering notes

    The keys are likely scanned as a matrix digitally.</P>

    The problem is indicative of a short between the key lines.</P>

    This could be a connector that has shifted sideways, wiring that has shorted on these two key lines.</P>

    If the keyboard is served by a ribbon cable, the cable may have pulled a bit and shorted the two lines.</P>

    Another thing is foreign material shorting the two lines. Could be almost anyplace including near the key contacts.</P>

    One needs the schematic.</P>

    The last thing would be a bad receiver chip that receives the data from these lines.</P>


    • #3
      Re: Yamaha E-70 issues, cross triggering notes

      I will add a little more information.</P>

      The keying circuits in matrix scanning are often failry high impedance and do NOT take a complete short to cause a problem like this... leakage as high as 10K ohms could cause this.</P>

      A couple of causes might be softdrink spilled on keyboard that has bridged etch of a circuit board.</P>

      The matrix has disconnect diodes that are driven by selection strobes. The disconnect diodes block a sneak path. The keys PROBABLY have two contacts. The contacts close at different times as the key is pressed. This allows the velocity of the strike to be measured to affect voices like pianos.</P>

      Usually 12 (with an extra one for the end of the keyboard) lines attach to the keyswitches. One line connects to every switch associated with a note. There will be a second set that ties to the second contacts of each note.</P>

      Through a disconnect diode, the octave banks are strobed. each 12 note section on the keyboards are joined at the other connection to the key switches. The keyboard is scanned by triggering ONE of the strobes and reading the 12 lines and then triggering the next strobe until all the octaves have been read. The rate of scanning the octaves is often thousands of times a second... certainly faster than you can play or notice any delay.</P>

      Hence, if a couple of these key lines get shorted or even leak between, the notes in every octave will display the same action. </P>

      As I mentioned, the problem could be anywhere from the receiver chip handling the key lines to the switches themselves. Being that the failure is after a move, I would look for foreign material shorting the key lines... like steel wool or metal shards first... Blow all the dust, etc. out first...</P>