HP Color LaserJet 8500 Service Manual - Page 205

Lifter operation The lifting plate in the 2,000-sheet input unit is held by two wires that are wound on four pulleys by the lifter motor. When the paper tray is open, the pulley gears disengage from the lifter motor gears, and the lifting plate is lowered by its own weight. The presence or absence of the tray is detected by switches SW701 through SW704 on the unit paper/tray size switch assembly. After the paper tray is closed, the lifter motor raises the paper stack into position; this action is detected by the PS34 sensor. The PS34 sensor also maintains the height of the paper stack. As pages are picked up by the rollers, the number of sheets decreases. Once the paper stack decreases to a certain level, the PS34 sensor registers a low condition. Then the paper deck driver turns on the lifter motor again and lifts the paper stack until the PS34 sensor registers sufficient paper in the tray. EN 2,000-sheet input unit 203