Xerox Phaser 6121MFP Service Manual page 91

Theory of Operation
Waste Toner Full Sensor
Waste toner near full and full conditions are detected by the waste toner near full
sensor, toner agitating screw, and an internal counter. An agitating auger is used
in the reservoir to provide the maximum waste toner storage capacity. A waste
toner near full condition occurs when light emitted from the sensor LED is
obstructed during its travel through the light guide.
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Rotation of the toner agitating screw causes the actuator to move up and down
via the float plate, so that the waste toner near full sensor detects "H" and "L"
signals alternately. When the amount of waste toner in the waste toner reservoir
exceeds a predetermined level, the toner agitating screw no longer rotates. This
stops the signal transitions from the waste toner near full sensor indicating a near
full condition.
A waste toner full condition exists when 200 images are reached after a waste
toner near full condition is detected. When the LED light is unblocked following
Imaging Unit replacement, the waste toner full condition is reset.
Phaser 6121MFP Service Manual 2-49