Figure 5-20 Paper Path The presence of paper in Tray 1 is detected by the Tray 1 Paper Sensor (PS105). Presence of paper in Tray 2 is detected by the Tray 2 Paper Sensor (PS101) for the HP LaserJet 4000, 4000 N, 4050 and 4050 N; and by the Upper Tray Paper Sensor (PS101) or the Lower Tray Paper Sensor (PS102) for the HP LaserJet 4000 T, 4000 TN, 4050 T, and 4050 TN. Both the size of the paper in the tray and the presence of a tray are detected by the three switches (SW600, 601, 602) on the Paper Size Detection PCA for the HP LaserJet 4000, 4000 N, 4050, and 4050 N, 5-34 Functional Information