128 Theory of operation C7085-90921
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
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
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