Yamaha electronic piano keying circuit broken
The interdigitated fingers are circuit traces coated with a very hard, non wearing, carbonized type conductive surface. If a board crack runs through this carbonized area, that is FATAL. Replace the circuit board.
Realize that these contacts drive high impedance CMOS circuitry so the contact resistance is often in the 200 to 1000 ohm range.
The silicone rubber domes contain a conductive rubber pills, often two of them. One contacts the fingers before the second and the time difference between those is the measure of "velocity".The silicone dome acts as the restoring force for the key.
The keyboard is scanned as a matrix. Strobe lines intermittently select the first and then the second of the finger patterns, ONE octave at a time. The octave, 12 notes worth, are read in parallel one at a time.
The diodes are "disconnect diodes" which preven sneak paths when more than one note is held that are in different octaves.
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