HP LaserJet 4 Service Manual - Page 138

Paper Feed System Note The LJ 5 printer designators differ as follows. LJ 4 / 4 Plus LJ 5 Multipurpose (MP) Tray Tray 1 Paper Cassette (PC) Tray Lower Cassette (LC) Tray Tray 2 Tray 3 The following paper paths are described in this section of the manual: • PC Tray (Tray 2) to Output Trays • MP Tray (Tray 1) to Output Trays The paper feed system is responsible for picking paper from either the PC tray (Tray 2) or MP tray (Tray 1) and delivering it to the image formation system, feeding it into the fusing station, and delivering the paper to the output tray (see Figure 5-16). The Paper Feed Assembly is a modular, replaceable paper-feeder mechanism which allows media to be input from either of four sources. The four paper input sources of the printer are: • The MP Tray (Tray 1) • The PC Tray (Tray 2) • The Lower Cassette (Tray 3) • The Envelope Feeder Each input has features which makes it the best choice for various applications. For instance, short media and heavy stock can be fed from the MP tray (Tray 1) because it senses media length and has a relatively straight paper path. Large print jobs can be fed reliably from the optional Lower Cassette (Tray 3). The Paper Feed Assembly contains a state machine which monitors input sensors and generates commands for the solenoids and motors on the Paper Feed Assembly. In addition, the Paper Feed Assembly communicates with the DC Controller through serial data lines. An illustration of this is M2, the Paper Feed Motor. M2 is controlled solely by the Paper Feed Assembly state machine. M2 begins rotation when the State Machine receives the correct set of conditions from its inputs and the serial data lines. M2 stops rotation when the Input Registration sensor (PS1) reports the presence of paper to the State Machine. The State Machine outputs the presence of paper to the DC Controller through the serial data line. 5-26 Functional Overview