Whwn I switch on my clavinova cvp20 the speakers

It sounds like an amplifier problem. This will not be user serviceable. You will need to find a Yamaha repairman in your area. Here is a link to the Yamaha Dealer locator site, and you local dealer can put you in touch with their preferred repairman.
http://usa.yamaha.com/dealers/

There are 2 possible things to look for - can't remember due to age of your instrument.

Look under the piano - about 20cm in from front corners, can you see a screw head set in a metal bracket. If so undo these and the top cover / lid will lift.

If not try : Close cover over keys, get a torch and look above the cover through the slit to the far left and right about 10cm in you might see a screw head - under these (1L 1R ) lift top cover / lid.

I hope this helps

It is likely the contacts on the headphone jack are sticking. If you're lucky, spraying some contact cleaner into the input will loosen it. Be careful not to get the spray onto the rest of the cabinet o the keys. If that doesn't work, you will need to take the unit apart so you cab get to the part to clean it.

Try resetting the piano.

Check out the link below. They will be able to fix it for you.
https://www.facebook.com/KeyboardSpecialistChicago

Try the headphone jack... if there is sound there, then it is either the speaker amplifier or a loose cable. It would be rare for BOTH speakers to fail completely.

Realize that it MAY be stretch tuned like a real piano. A real piano is tuned increasingly sharp above middle C and increasingly flat below middle C. At the ends, the the off tuning is about 20 to 22 cents sharp and flat. The Clavinova should emulate this. In a real piano this makes it sound better and prevents some cross coupling of harmonics. Read up about stretch tuning on the internet. The Clavinova gets its reference from a quartz crytal oscillator and they just dont' get out of tune.

The Clavinovas are maintainable. Since you have not described the distortion we can't give much help. If there is difference between notes on the keyboard, the contacts may be getting dirty. If the audio is distorted for everything, the amplifier or speakers may need maintenance.

Hi, did you manage to sort your problem as the same thing has happened to my clavinova (same model). Thanks.