Phaser 6300/6350/6360 Color Laser Printer Service Manual 2-11Theory of OperationLED Light Density CTD (ADC) Control SensorThe CTD (ADC) Sensor is a photo-reflective sensor that emits light from anLED and detects the reflected light returning from the Transfer Roller. TheCTD (ADC) Sensor reference voltage (reflected light density) is establishedwhen both the sensor and the Transfer Roller are clean and free of defects.The light emitted from the LED is controlled so that the reflected light densitymeets the reference value.LED light emission control is implemented in two ways:■ Sets the light density so that the light reflected satisfies a specificvalue.■ Adjusts the subsequent light density to be within a specific tolerancevalue.1. Light Density SettingThe reflected light density can vary greatly if the Transfer Roller has just beenreplaced or the CTD (ADC) Sensor has just been cleaned, or is dusty withwaste toner. To compensate with this variance, the light density is reset eachtime the power is turned on or a door is opened.When the output of the CTD (ADC) Sensor does not meet the referencevalue, the intensity of the LED light emissions are increased gradually and theLight Density Setting is adjusted. If the light density is increased to themaximum and output of the CTD (ADC) Sensor does not reach the referencevalue, a warning message indicates the sensor is dirty. If the sensor outputremains above the reference value, a fatal error reports that the sensor isfaulty.2. Light Density AdjustmentAt the execution of Automatic Density Control, the Light Density Adjustment ismade just before the toner patches for toner density control are generated.Light is emitted from the LED using the current Light Density Setting, to checkif the output value of the CTD (ADC) Sensor is within the specified range. Ifthe output value is low, light density is increased. If the output value is high,light density is decreased.If the output value is less than the first lower limit, a warning messageindicates the sensor is dirty. If the output value is less than the second lowerlimit, a Fatal Error signals that the sensor is faulty and the printer stopsprinting.
