We purchased a new Clavinova CLP810s digital piano for our home back in December 1999. The piano sound is great and the instrument performed fine initially, unfortunately, a few months after the piano arrived,
two issues started to affect the joy of playing it. Years later and thanks to knowledge shared by people in the internet, I was able to diagnose and start the repair of these two failures.
One by one, a number of keys in the keyboard became silent initially after powering up the piano. Playing the silent key a number of times during a few minutes, would make the key play back normally. The key became silent again when the piano was powered fresh the next day. F#3 was the first silent key, months later D#3 failed the same way, and eventually B0, E1, G2, A2 and E3 joined. Depending on the key of the tune being played, silent notes were less or more annoying.
I found that repeatedly playing a silent key made it sound again for that session, but this procedure was distracting and tedious. Sometimes a silent key would just play just fine, as if the problem was gone, but next day it would become silent again.
On September 2014, I found the CLP810s service manual in owner-manuals.com (Enter CLP810s in the search box, click on GO). This helped understanding the key scanning circuitry, and figuring out that simply pressing and holding the silent key for about a minute, like by placing a small heavy object over the key, would make a silent key play normal for that session. To discard if the issue was related to worn key contacts, I opened the piano, unmounted the keyboard, and cleaned the contact bars of the silent keys with isopropyl alcohol, but this did not fix the problem.
The issue was later found to be caused by an unusually high resistance value in the lower half of the so-called rubber contact strip, as compared to the low resistance value on its upper half. The lower half is used by keys A0 through F#3, the upper half by keys G3 through C8. The high resistance is independent of the frequency of use of the key: not a single key on the upper half of the contact strip has ever failed. While the high resistance produces the failure, heating of the circuit components helps preventing it.
Playing the piano keys became noisier over time. Even with the piano powered off, the keys themselves make a considerable amount of mechanical noise while playing a tune. The instrument sounds as if it is old or worn down, because the keyboard noise mixes with the piano sound.
The video The Simple Repair of a Yamaha Clavinova to reduce Keyboard Noise by Gunwharf in YouTube (7' 52''), explains that the keyboard noise is caused by a worn down felt strip, and shows how to replace this part by yourself at home.
I ordered one VY693500 Rubber contact strip and one V764010R felt stopper from the Yamaha office in Mexico City on May 14th. Receiving these parts from Japan takes about 4 week, then they will ship them to our home. I hope that both obnoxious failures will have an end soon.