HP LaserJet M9040/M9050 Service Manual - Page 135

Flatbed document size detection Figure 5-16 Flatbed document size detection Sensor names ● Flatbed document detection sensor: SCNSIZE1S (only detects the document on the glass) ● Flatbed document size detection sensor (1): SCNSIZE2S size sensor ● Flatbed document size detection sensor (2): SCNSIZE3S size sensor ● Flatbed document size detection sensor (3): SCNSIZE4S size sensor The sensors send signals to the SCB. The signals are transferred through the intermediate PCA to the CP. The CP calculates the size of the document based on the signals from the sensors. The flatbed document sensors are located in the same positions on the 110 vdc and 220 vdc products. To determine the sizes of larger documents, the product searches for the cold reset paper size. For example, it will detect ledger if it is set to letter, and it will detect A3 if it is set to A4. Functions operation When a document is placed on the glass and the ADF unit is closed or at an angle of less than 30 degrees, the SCB begins to detect the presence and size of the document. The SCB monitors outputs from the flatbed document detection sensor (SCNSIZE1S) and the flatbed document size detection sensors (SCNSIZE2S, SCNSIZE3S, and SCNSIZE4S). The SCB passes the signals from the sensors to the CP. The reflecting sensor detects the presence and size information of the document based on whether the photoreceptor can receive the emitted light from the luminous body of the sensor. When a document is on the glass, the document reflects the emitted light and the photoreceptor can receive the reflected ENWW Basic operation 117