I sure can, I don't need an immediate response. Here's the scope of the work:
Unplug it, and turn the power switch on to drain residual power. Wait 30 seconds.
for the repair manual. The download link is just below the picture, and it takes a minute to show up. Refer to page 14 for disassembly. You need to get to the back of the keys.
You'll notice that when a key is pressed, the back side of it goes up and strikes a pressure sensitive pad, which makes the sound. Those get clogged with dirt and stop working over time. Give those a good cleaning with compressed air, and give your entire piano a good cleaning with it as well. Hold the air spray 2 feet away from any circuitry when spraying.
Also give the keys themselves a good cleaning with the air, they tend to be the dirtiest of the piano.
Feel free to plug it in and test the keys at this point. If they are still not working, there are Yamaha parts in the UK, and they are cheap. 0844(NNN) NNN-NNNN/strong>
We'll have to discuss the out of tune keys after the cleaning. Let me know how it ends up.