HP P2055 Manual

Laser failure detection
The optical unit failure detection sensor manages the laser/scanner unit failure-detection functions. The
DC controller identifies the laser/sca nner unit failure and notifies the formatter if the laser/scanner unit
encounters the following conditions:
● Scanner motor failure
● BD failure
ENWW Laser/scanner system 89 

Image-formation system
Laser printing requires the interaction of several different technologies, including electronics, optics, and
electrophotographics, to provide a printed page. Each process functions independently and must be
coordinated with the other product processes. Image  formation consists of the following five processes:
● electrostatic latent-image formation
● developing
● transfer
● fusing
● drum cleaning
The five processes contain seven steps.
Figure 5-8  Image-formation system
2....

Step 2: Laser beam exposure
The laser beam scans the photosensitive drum to neutralize negative charges on parts of the drum. An
electrostatic latent image is formed on the  drum where negative charges were neutralized.
Laser beam
Unexposed area Exposed area
Step 3: Developing
The developing cylinder comes in contact with the  photosensitive drum to deposit toner onto the
electrostatic latent image.
NOTE: The charges on the exposed area of th e drum are shown as positive in Figure 5-10 Developing
on page...

Figure 5-11  Transfer
Transfer bias Media
Transfer roller Photosensitive
drum
Step 5: Separation
The elasticity of the print media causes its separa tion from the photosensitive drum. A static charge
eliminator aids separation by we akening any electrostatic adhesion.
Figure 5-12   Separation
Media
Transfer roller
Photosensitive
drum
Static charge eliminator
Step 6: Fusing
The dc negative bias applied to the fusing film strengthens the holding force of the toner on the print
media and prevents the toner...

Figure 5-13  Fusing
Fusing bias
Fusing film
Toner
Pressure roller
Fusing heater
Media
Step 7: Drum cleaning
The cleaning blade scrapes the residual toner off the photosensitive drum and deposits it into the waste
toner case.
Figure 5-14  Drum cleaning
Toner collection box Photosensitive
drum
Cleaning blade
ENWW
Image-formation system 93 

Pickup/feed/delivery system
The pickup/feed/delivery system consists of several types of feed rollers and sensors. The DC controller
uses two motors and two solenoids to drive the ro llers. Three media-detection sensors detect media as
it passes through the product. If media does not r each or pass each sensor within a specified period,
the DC controller determines that a jam has occurred and alerts the formatter.
Figure 5-15   Pickup/feed/delivery system
M1SL1
SL3
SL2
PS912 PS916
PS914
PS913
PS911...

Jam detection
The product uses the following sensors to detect the presence of media and to check whether media is
being fed correctly or has jammed:
●Top sensor (SR912)
● Fuser delivery sensor (SR915)
● Duplex reverse sensor (SR918)
Figure 5-16   Jam detection
PS912
PS915
PS918
: Simplex media path
: Duplex media path (HP LaserJet 2050 series printer only)
ENWW Pickup/feed/delivery system 95 

96 Chapter 5   Theory of operationENWW 

6 Removal and replacement
●Introduction
●
Removal and replacement strategy
●
Electrostatic discharge
●
Required tools
●
Before performing service
●
After performing service
●
Post-service test
●
Print cartridge
●
Tray 2 cassette
●
Rollers and pads
●
External panels, covers, and doors
●
Internal assemblies
ENWW 97 

Introduction
This chapter describes the removal and replacement of field-replaceable units (FRUs) only.
NOTE:Your product might not appear exactly as the on e shown in the photos in this chapter. For
example, the color of the external panels and covers  might be different than your product. However, the
procedures in this chapter are valid for both th e HP LaserJet P2035 and the HP LaserJet P2055.
Replacing FRUs is generally the reverse of removal.  Notes and tips are included to provide directions
for...