HP LaserJet Pro MFP M521 - Copy; Make a single copy; Make multiple copies; Copy on both sides (duplex)

Table of contents
1 Theory of operation .......................................................................................................... 1
Basic operation ........................................................................................................................ 2
Major systems ........................................................................................................... 2
Product block diagram ............................................................................................... 2
Sequence of operation ............................................................................................... 3
Normal sequence of operation ..................................................................... 3
Formatter-control system ............................................................................................................ 4
Auto on/Auto off mode .............................................................................................. 4
Input/output ............................................................................................................. 5
CPU ........................................................................................................................ 5
Memory ................................................................................................................... 6
Firmware ................................................................................................... 6
Nonvolatile memory ................................................................................... 6
Control panel ........................................................................................................... 6
Engine-control system ................................................................................................................ 7
Motors, fans, clutches, solenoids, switches, and sensors ................................................. 8
DC controller operations .......................................................................................... 15
Fuser-control circuit .................................................................................................. 17
Fuser failure detection ............................................................................... 18
Fuser temperature control .......................................................................... 19
Fuser protective function ............................................................................ 20
Low-voltage power supply ........................................................................................ 21
Overcurrent/overvoltage protection ............................................................ 22
High-voltage power supply ....................................................................................... 23
Laser/scanner system .............................................................................................. 24
Laser failure detection ............................................................................... 25
Image-formation system ........................................................................................................... 26
Electrophotographic process ..................................................................................... 26
Image formation process .......................................................................................... 27
Latent-image formation stage ..................................................................... 28
Primary charging ...................................................................... 28
Laser beam exposure ................................................................. 28
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