HP 4550 Service Manual - Page 130

Table 5-6 Fusing and delivery unit components Reference Description M1 Fusing motor PS6 Fusing unit pressure release sensor PS7 Delivery unit paper sensor PS9 Face-down bin full sensor Duplex unit paper path Theory The duplex unit enables printing on both sides of a page. With two-sided printing, known as duplexing, the back side of the page is printed first. Then the page is sent through the duplex unit, where it is flipped over and sent back through the printer for printing on the front. Power supply There are two power supplies for the duplexing unit: power supplied by the printer and power supplied by the internal power supply. The CPU requires +5 V of power to be supplied from the printer. This power is also used to supply power to the paper feeder. The external power supply provides +24 V and +5 V, and is used to drive the motors, solenoids, and sensors. Operation Paper is fed into the duplexing unit by the duplex feed rollers, which are rotated by the duplex feed motor (M3101). The paper is reversed by the reversing roller, which is rotated by the reversing motor (M3102). The paper is then fed into the printer by the duplexing unit feed roller after the side registration roller is adjusted by the side registration guide (see Figure 5-32). Figure 5-32 Reversing and duplex pick-up operation 128 Theory of operation C7085-90921