HEWLETT PACKARD (HP) LJ4050
Service Manual

and by the six switches (SW600, 601, 602, 603, 604, 605) on the Paper Size Detection PCA for the HP LaserJet 4000 T, 4000 TN, 4050 T, and 4050 TN. While the Main Motor rotates, the Tray 1 Pickup Solenoid (SL102) is turned on, the Tray 1 Pickup Roller rotates, and a sheet of paper is fed into the printer. The paper passes the pre-feed roller, which compensates for the skew of the paper. After the top of page sensor (PS103) detects the leading edge of the paper, the horizontal synchronization signal (/TOP) is sent from the Engine Controller Board to the Formatter. After the Formatter receives the /TOP signal, the /VDO signal is sent; this synchronizes the leading edge of the image on the Drum with the leading edge of the paper. The paper goes through transfer, separation, and fusing stages, passes through the delivery unit, and is delivered to the Top Output Bin or Rear Output Bin. There are four photo-interrupters (PS102, PS103, PS106, PS501) in the paper path that detect the presence of paper. If the paper does not reach or pass these sensors within a prescribed time interval, the microprocessor on the Engine Controller Board notifies the Formatter of a paper jam.

Clutches and Sensors
See �Reference Diagrams� starting on page 7-84 for locations of switches, sensors, and clutches.

Paper Feed System 5-35