The f and b keys after middle C does not make any sound when played. Where can I start trouble shooting?

Normaly this can be a battery problem or the capacitors are getting worn out

try to clean under neath of those particular keys very gently with cotton buds .2)is it the case with in all the octaves 3) has the K.B been in humid places

Call Yamaha at 714-522-9000 and ask for a tech who works in your area. Attempting self repair could void any garuntee that is covering the problem.

I am sure it can be repaired. First thing is to check the power supply. Here is a servuice manual for a CLP380... You did not mention the modelk number of your unit. I may be able to find exact manual.

http://elektrotanya.com/yamaha_clp-380.pdf/download.html

Scroll; down to "get manual" and click to download. IGNORE other download links.

The key contact has gotten contaminated. They are a black conductive rubber pill pressed against circuit traces on a board bellow the keys. Remove that key and maybe others to get at the contacts in silicone strips. Clean ONLY with 99% isoprophyl alcohol and Q tips. Clean both the pills (two per note) and the circuit traces they touch. You have to release the spring at the back of each key to remove the key.

Thisis hard to troubleshoot... The keyboard insynths are usually scanned as a matrix... If a disconnect diode has failed, then wrong notes can be triggered. There is USUALLY rows of the diodes on the circuit board where the keys hit. There are usually TWO contacts per key in order to sense key velocity. The lkey contacts are usually conductive rubber pills pressed against circuit traces under the keys. One sometimes needs to clean these contacts using 99% isoprophyl alcohol and Q tips.
I would do further testing of ALL combinations of notes played together to see if possibly any others show up as that could point to a particular failure.

If you can find the C-below-middle-C ?

Put your small finger on C,
your next finger on the next white key: D,
your middle finger on the next white key: E
your index finger on the next white key: F
your thumb on the next white key: G

Lift your fingers away from D and F -- to keep this simple -- all we did was identify the D and E and F and G keys, relative to the C key.

Press C and E and G (small, middle, thumb)
to play a "major" chord in C.

Move your fingers "up":
C to D, E to F-sharp, G to A,
and play a "major" chord in D.

Move your fingers "up":
D to D-sharp, F-sharp to G, and A to A-sharp,
and play the chord in D-sharp (usually called 'E-flat').

Move your fingers "up":
D-sharp to F, G to A, and A-sharp to C,
and play the chord in F.

Move your fingers "up",
F to G, A to B, and C to D,
and play the chord in G.

Go back to the starting position (C-E-G),
and move "down": C to B-flat, E to D, and G to F,
and play the chord in B-flat.

So far, you have C-major, D-major, E-flat-major, F-major, G-major, and B-flat-major.

There are more chords, but most pop-music is in one of these keys.

Give it a try.

A lot of left-hand stuff is just the small-finger and thumb, omitting the middle finger, e.g., C&G,
to avoid a too "muddy" sound.

Or, "stretch" your hand: C-and-G-and-the-next-higher-C.

Try the reset procedure on page 5 ( last page ) of this pdf document:http://www.dgaudiorepair.com/PDF%20Files/HARD%20RESET%20for%20Current%20KURZWEIL%20.pdf Hope this helps. Note the first procedure says highest white key. I'd do the second procedure.

That doesn't sound good. It sounds as if the processor is locking up and that might only be fixed by replacing the main board. Sometimes this happens if a unit gets fried by static electricity.

But before giving up, I would open up the unit and check for loose cables and connectors internally. If there are chips (IC's) that are socketed on circuit boards, push them down firmly. Things may start working again.

Do a factory reset. First try pressing the + and - buttons simultaneously.

Look in your user manual for a complete factory reset and do that.