HP LaserJet 4 Service Manual - Page 360

As the paper moves from the Switchback Assembly, it is picked up by the rollers that are operated by the Holding Tray Input Stepper Motor. The Input Stepper Motor moves the paper into the Holding Tray. When the paper moves the flag that controls the Holding Tray Paper Sensor, the Duplex Control PCA turns off the Input Stepper Motor, and the paper stops moving. The paper remains in the Holding Tray until the print engine signals the Duplex Control PCA that it is ready to print the second side. The Duplex Control PCA will then turn on both the Holding Tray Input Stepper Motor and the Holding Tray Output Stepper Motor. These motors will move the paper out of the Holding Tray into the paper input of the print engine. The paper is then printed on the second side. When the paper exits the Fuser Assembly, the Switchback Input Guide routes the paper directly to the printer's output tray. 3 4 2 5 1 6 7 10 8 9 Figure A-2 Duplexer Major Components A -4 Duplexer