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Do normal indicator lights come on, and does the display show responses to settings but the buttons, etc.? Is it simply that there is no sound?
(I regret that I am not able to offer Live Phone Call service at this time; However, your request is still open to other Experts in this category, and one of them may pick up on it at any time.)
If all else seems normal but there is no sound, check to make sure MIDI Out (if your model even has that capability) is not enabled - which could shut Off the sound.
If your model has a headphone jack, check on it - it might cut off the sound output, also - except through headphones - even if no headphone is plugged into it, if the headphone jack's internal switch has become stuck or jammed in the sound-shut-off position. (The ideal way to check this is to simply plug headphones into it, and see if they produce sound, then unplug them and see if the sound is now working.
After that, unfortunately (and of course, if the volume is not at minimum) you may have an internal failure of the audio amplifiers. And that would mean the Clavinova would need repair. If you get to this point and are interested in having it repaired, please tell me your local zip code, and I will research servicers of Clavinova type keyboard/piano/organs in your region.