Yamaha clavinova won't play C natural in any octave

There are a number of fuses on the main power board ( by transformer ) the sizes differ depending on the country of use but are clearly marked on the board.

REMEMBER TO UNPLUG FROM THE MAINS BEFORE OPENING - if in doubt seek the advice of a qualified electrician

Hi, Could be a lot of different things.

Does it play through headphones?
If so this implies an amplifier issue.
Does it play when you press the demo button - if so it could be a keyboard issue.

Carry out a factory reset by holding down highest note whilst turning on. Watch screen does it report anything?

Let me know what it says and I will try and help.

call up Yamaha. They will fix it for free as it is a manufacturing fault.

Without power to the unit no sound should be generated. Make sure there are no other connections.

MAYBE you have a wall transformer behind it that is buzzing. MANY wall transformers develop buzz.

Another source is flourescent lights and even some of the low voltage halogens have noisy transformers in the base.

The control panel hinges upwards and you have to move the keybed back a bit to get at the jack. All the screws on the bottom for the keybed. I'm not sure where the ones for the control panel are.

A contact rubber for CVP-35, part number VS549800 will work, that's how I fixed my sensor problems on my CLP-360.

hi...
Your L/R jacks in the back need to connect to the "line-in" connector on your sound card.
I think the jacks on the Clav are 1/4 inch. Go to Radio shack and ask for an adapter that will take two 1/4 inch plugs/cable and convert it to a 1/8 inch stereo plug.
The Midi connects From (keyboard) To (soundcard)
Cables are available at any music store

It is a design fault. A technician advertising on the net informed me i can get it fixed by him and yamaha will pick up the fee.

This is a common problem with Yamaha keyboards. The problem is caused by worn-out rubber contacts in the keyboard assembly. In my old Clavinova CLP-500, there was one long rubber contact strip under the keys with two parallel strips of semiconductor material. The Clavinova circuitry determines key velocity by measuring the timing between when the key hits the first and second strips of semiconductor material. The harder you play a key, the less time it takes the key to hit the second semiconductor strip after hitting the first.
After years of playing the keyboard, the keys eventually cause tears in the semiconductor material and this messes up the timing measurement for key velocity. The only solution is to take the keyboard apart and replace the rubber contact strip with a new one.
I got rid of my CLP-500 four or five years ago and got a new CLP-170. The CLP-170 is now having exactly the same problem that the CLP-500 had. Yamaha has re-designed the rubber contacts in the CLP-170 so that there are now eight individual contact strips instead of one long one. The problem is essentially the same, though. You have to take the keyboard apart and replace the worn out rubber contacts.
Here are the part numbers for the rubber contacts that need to be replaced in the CLP-170: V8286600 Rubber Contact, 12 keys, D-C#   Qty. 6 V8286800 Rubber Contact, 11 keys, A-C#   Qty. 1 V8286700 Rubber Contact, 5 keys, D-C   Qty. 1
I suggest you also get a copy of the CLP-170 service manual, part number 001677. It has descriptions of all the steps necessary to take the thing apart and put it back together again. You'll also need a "rod" (which is just a long dowel), part number TX000670. Before you take the circuit boards off the keyboard assembly, you have to insert the dowel between the keys and the frame to keep the keys from falling back and getting in your way. A 5-foot long 1/4-inch dowel will probably work. (I haven't yet taken apart my CLP-170, and I don't have Yamaha's "rod," so I'm not sure if 1/4 inch is the right size or not. I'll report back here if it's not.)
Good luck, Howard