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I just worked on a Clavinova's pedal assembly. Here's more than you ever wanted to know about how it works:
Each pedal presses a rubber plunger down so it connects with a matrix on a printed circuit board. The plungers have tips that are not themselves conductors but that induce current to flow through the matrix. When you press a pedal it puts from 20 to 40 ohms across the two cable leads associated with that pedal, different resistances for each pedal. Unlike many plug-in pedals, which are just on-off switches, these pedal circuits bring the resistance down and raise it gradually, probably to emulate the mechanical properties of a real piano.
The piano I worked on was a Clavinova 85A. It had the same setup as a much older one I worked on several years ago. Yours might be different. This discussions assumes it is not. If all three pedals quit at once, the problem might be in the cable. It might have come loose from the circuit board down in the pedal assembly. The quickest way to check is to lay the piano on its back and look at the bottom of the assembly. You should be able to see where the cable connects to the circuit board. If it is in place, test the resistance across the pins in the connector that fits into the base of the piano. There are four pins. One is common. The other three are for the three pedals. On the 85A, the white lead is common. White and yellow are the sustain pedal and white and black are the soft pedal. The red lead, which is not connected at the circuit board is, presumably, for sostenuto, which is not installed on the 85A.
If there is no resistance when you press the pedals, the problem is in the assembly. Maybe the circuit board is shorted out or even broken, in which case you have to replace the circuit board. Those assemblies are tough, but a rough player can do some damage. That's why I had to fix this one.
If the corresponding lead resistances, tested at the connector that goes into the piano body, drop from infinity to 20-40 ohms when you press the pedals, the pedal assembly is okay, and the problem is inside the piano body. Bigger job. You have to take the piano apart and find out what came loose inside the piano or what component went bad. Might be in part of the circuit that provides power to the assembly. I don't have any details on that part, and, unless something is obviously burnt out, you probably need get a Yamaha technician to repair it.
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