Ricoh FW780 Service Manual - Page 54

Rev. 5/95 4.4.3 Toner Density Sensor Toner Density Sensor 2 Control 1 Circuit 3 4 Main Board CN104-A11 CN104-B20 CN104-A10 CN104-B21 [12V] TS Control TS. FB GND Coils The toner density sensor circuit controls the amount of toner in the developer mixture. The toner density sensor is powered by 12 volts from CN104-A11 of the main board. (The potential of CN104-A11 is 24 V when the connector is disconnected.) The sensor's sensitivity is based on the feedback signal applied from CN104-A10. The input signal to the sensor passes from the main board at CN104-B20. The active sensor element is a very small transformer with three coils. When iron ferrite (carrier) is near the sensor element, the inductance of the coils changes, causing the current through the transformer to change. As the amount of toner in the developer increases, the effect of the carrier particles decreases and the voltage applied to CN104-A10 decreases. Conversely, when the toner concentration drops as toner is used up, the effect of the carrier on the sensor coils increases and the voltage at CN104-A10 increases. SM 2-18 A163