Yamaha Disklavier E3 Series Maintenance Handbook page 8

The CSP unit converts MIDI playback data from the
control unit to PWM data for the key drive (or pedal
drive) unit, and relays it on to the drive sheet in the
key drive unit. The FET drives the key solenoids.
(Also the pedal solenoids are driven by FET.) Two
temperature sensors for thermal protection are
installed on the pedal drive unit and one sensor is on
key drive unit, and activate when the unit reaches
120ºC (key drive unit : 100℃). Corresponding PWM
output to the pedal drive is stopped when excessive
temperature activates the sensor.
Turning the power OFF and letting the temperature decrease will restore operation.
Also, individual poly switches installed on the keyboard and pedal drive FET circuits
shut down the circuits when excessive current is detected. (The switch resets when
there is no power surge present.)
4. Sensor Unit
The sensor unit consists of the key and the hammer sensor (DGB1K has only key
sensor), which detects key and hammer movement during performance, and the pedal
sensor, which detects pedal movement (damper, shift, sostenuto).
4-1. The key sensor consists of the key sensor sheet,
optic fiber,
movement causes the acrylic shutter attached
to the underside of each key to break the LED
light beam as it passes from the optic fiber to
the sensor head.
The key shutter is printed with a gradation,
which goes from solid (black) in its upper
portion to thin (transparent) in the lower, that
changes the amount of light received by the
optical sensor as keyboard movement causes
the shutter to break the beam of light. The
level of transparency decreases as the keys are
depressed.
This is how key movement is detected.
The key sensors also function with key feedback control during automatic playback.
light source/receiver.
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Pedal drive unit, without cover(GP)
Position of the key shutter and the sensor
KEY OFF
Key
KEY ON
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