#1845099 - 11/22/07 01:11 AM
Roland Piano, Bad Key
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rchandos
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Registered: 11/22/07
Posts: 2
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One of the G keys on Roland HP-100 piano has lost all dynamics, plays full volume no matter how hard you strike it. Have solved this recurring problem with other Gs in past by replacing rubber key contact strip, even though nothing visibly wrong with it. But Roland no longer sells them. Any suggestions appreciated.
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#1857454 - 12/16/07 12:05 AM
Re: Roland Piano, Bad Key
[Re: rchandos]
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rchandos
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Registered: 11/22/07
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Well, I seemed to have solved my own problem. In case anyone else encounters this, here is how: I applied a few drops of electrically conductive glue (catalog # WG-1 from All Electronics, http://www.allelectronics.com, $3.98 for a small bottle)to the contacts of the rubber key strip, let them dry overnight, and put them back in the piano. After failing to find replacement key strips, I decided to try and figure out why mine weren't working right. I turned the little rubber key switches, which resemble small rubber plungers--the same sort of switches you find in remote control keypads--upside down, measured across the little circular contact disks with an ohmmeter, and found that the bad one was an open circuit--no conductivity--while the good ones had some measurable resistance. This causes the loss of dynamics, I guess, because there are two such switches that must make contact each time you depress a piano key: one nearer the rear of the key and one nearer the front of the key. Due to the geometry of the pivoting key, the switch nearer the front (nearest the player) makes contact first, and the other one makes contact a short time later--just how much later depends on the key velocity: a short time later means a higher velocity, and vice versa, so the electronics (microprocessor)measures the delay between the contacts closing and uses it to compute the volume at which it will play the note. Now if the front switch (that normally fires first) is bad and never makes contact, then the key just never sounds at all, because the electronics (microprocessor) never gets a signal telling it to start timing the delay. I found that this happened when I put the dead key contact in the front. But if the rear switch contact is bad and never makes contact, then, for some reason, you get the jolting full volume effect, due, I guess to the way the processor interprets the signals from the contacts, and what it does after it gives up waiting for the second switch to fire. In any case, the piano seems to work fine again.
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