My casio px555r has eight consecutive notes which are twice as loud as all the other keys and not touch sensitive. It is the same for all the sounds. When I turn the sensitivity control to off, the problem disappears, but then of course there is no touch sensitivity.,

This link might help.

https://www.google.com/search?q=Casio+Privia+px-100%2C+loud+key

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What model? Diodes are either burned up (but you would see the ends still present) or missing because they aren't applicable to that model. It's more likely the rubber pads under the keys need to be replaced

the contact rubbers might be broken or the rubber itself is wornout because of usage or there is dirt in it.. its lose its touch response, the best easient way is to replace the contact rubber.

Hi, This is very likely to be a dirty key contact.
If the loud key is not touch sensitive or by turning the touch off, if all the keys are the same volume then this points to a dirty key contact.
All the best, Chris the Fader.

I just fixed mine, it was making the loud sounds and had seemed to have lost the sensitivity. Take out all the screws on the outside, then the sides can come off. That gives access to the inside where you can take out a few more screws (easily seen) and open it all up. The keys themselves just snap in, so two small screwdrivers or strong fingernails can pop them back out. Clean the rubber contacts (they look like little sockets) with Q-tips and rubbing alcohol, then replace the keys. If you take out the white keys of an octave first, then the black keys (keeping them in order) it is a lot easier.

You MAY be confusing touch sensitivity with VELOCITY sensing. Touch sensitivity is PRESSURE put on AFTER the note sounds that causes modulation. VELOCITY is what is used for example to control the loudness of pianoo notes depending how fast they are struck. VELOCITY sensing is done by using TWO contacts at every key... one closes first. IF one of these gets dirty, FULL velocity will be sensed and it will be LOUD. The contacts can be cleaned using ONLY 99% isoprophyl alcohol and Qtips after MUCH disassembly of the keyboard. The contacts are conductive rubber pills in silicone rubber domes. Clean boththe contacts and the circuit traces they pres down onto.

You can try to dry the inside of the keyboard by taking the end of the key board off.
Take a hair dryer and place it at the end of the keyboard and let the air dry out the fluid this may take some time depends on how much fluid you have inside.
Do not use the dryer on high because the heat will warp the bed the keys fit into, this will damage the board which cost about $ 400.00 to repair. Do not turn on the key board while the fluid is still inside this can also damage the keyboard. I belive you have already turn it on because you said eight keys do not work.Do not open the keyboard because the keys will be hard to put back in the grooves the way they were.

You can try and have it repaired at American Perfect Crystal Corporation
Casio Parts Distributor 520 Eight Ave. 2nd Floor
New York, New York 10018
212-246-8292
800-345-0537
[email protected]
www.americanperfit.com

They will charge about 50-89 dollars to check it for you and if its reparable the checking fee will go toward the repair.
I wasted kool-aid in my casio privia while the keyboard was off, but made a grave mistake because I tried to repair it my self with the hair dryer at a high level. I was told that the major board was warp, that being said try not to do self repair.

I have the same problem.The rubber panel that is used for touch sensitivity (under the keys) inside the case wears down in time. You can split it and shift parts but you eventually will have to replace it. This rubber panel is very hard to get. Good luck.

Most of these have VELOCITY sensing and that involves two contacts per note. If the velocity sense on those notes is somehow not working, broken wire or trace on the board or short that MIGHT cause your problem.