HP 8550 Service Manual - Page 312

Lifter operation The lifter in the side HCI is suspended by two wires. The wires are operated by the lifter motor (M1: stepping motor). When the right upper cover open sensor (PS1) detects that the upper right door has been opened, the deck controller PCB reverses the lifter motor and lowers the lifter until the lower limit lifter switch (MS3) goes on. When the right upper cover opening sensor (PS1) detects that the upper right door has been closed, the deck controller PCB rotates the lifter motor forward and raises the lifter until the upper limit lifter sensor (PS4) goes on. As the number of sheets in the stack are reduced by paper being picked up, the upper limit lifter detection sensor goes off, the deck controller PCB rotates the lifter motor forward and raises the lifter until the lifter upper limit goes on. When the lifter upper limit sensor does not go on within the stipulated time after the lifter starts to rise, the deck controller PCB assumes that a lifter breakdown has occurred and transmits an error code to the option controller PCB in the copy module main unit. Figure 194. Lifter operation 310 Chapter - 5 Theory of operation EN