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
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							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. Laser-beam exposure
Fusing
6. Fusing
Delivery 7. Drum cleaning
3. Developing
1. Primary charging
Pickup
4. Transfer 
5. Separation
Transfer
Latent image formation
Media path
Direction of the drum rotation
Block
Step
Drum cleaning Developing
Step 1: Primary charging
DC and AC biases are applied to th
e primary charging roller, which tran sfers a uniform negative potential
to the photosensitive drum.
Figure 5-9  Primary charging
Primary charging bias
Photosensitive drum
Primary charging roller
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							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 91. The charges are actually negat ive, but they are more positive than the charges on the
developing cylinder.
Figure 5-10   Developing
Developing bias
Blade
Developing roller
Photosensitive drum
Unexposed area
Exposed area
Exposed area
Unexposed area
Toner acquires a negative charge thro
ugh friction from the developing cylinder and the blade. When the
negatively charged toner comes in contact with the  drum, the toner adheres to the electrostatic latent
image. The image on the drum becomes visible because of the toner.
Step 4: Transfer
The transfer charging roller, to which a dc positive bi as is applied, imparts a positive charge on the print
media. When the print media comes in contact with  the photosensitive drum, the toner is transferred to
the print media.
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							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 from scattering.
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							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
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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
PS915
PS918
M1Main motor
SL1Tray 1 pickup solenoid
SL2Tray 2 pickup solenoid
SL3Duplex solenoid (HP LaserJet P2050 Series Printers only)
PS911Tray 3 media sensor (HP LaserJ et P2050 Series Printers only)
PS912Top-of-page sensor
PS913Width-detection sensor
PS914Tray 2 media sensor
PS915Fuser delivery sensor
PS916Tray 1 media presence sensor
PS918Duplex sensor (HP LaserJet P2050 Series Printers only)
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							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
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							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 difficult or critical  replacement procedures.
HP does  not support repairing individual subassemblies or troubleshooting to the component level.
Note the length, diameter, color, type, and placement  of each screw. Be sure to return each screw to
its original location during reassembly.
Incorrectly routed or loose wire harnesses can inte rfere with other internal components and can become
damaged or broken. Frayed or pi nched harness wires can be difficult  to find. When replacing wire
harnesses, always use the provided wire loops, lance points, or wire-harness guides.
Removal and replacement strategy 
WARNING! Turn the product off, wait 5 seconds, and then  remove the power cord before attempting
to service the product. If this warning is not followe d, severe injury can result, in addition to damage to
the product. The power must be on for certain functional checks during problem solving. However, the
power supply should be disconnected during parts removal.
Never operate or service the product with the pr otective cover removed from the laser/scanner
assembly. The reflected beam, although invisible, can damage your eyes.
The sheet-metal parts can have sharp edges.  Be careful when handling sheet-metal parts.
CAUTION:Do not bend or fold the flat flexible cables (FFCs) during removal or installation. Also, do
not straighten pre-folds in the FFCs. You must Make sure that all FFCs are fully seated in their
connectors. Failure to fully seat an FFC into  a connector can cause a short circuit in a PCA.
NOTE:To install a self-tapping  screw, first turn it counterclockwise to  align it with the existing thread
pattern, and then carefully turn it clockwise to tigh ten. Do not overtighten. If a self-tapping screw-hole
becomes stripped, repair the screw-hole or replace the affected assembly.
Electrostatic discharge
CAUTION: Some parts are sensitive to electrostatic  discharge (ESD). Look for the ESD reminder
when removing product parts. Always perform service  work at an ESD-protected workstation or mat. If
an ESD workstation or mat is not available, groun d yourself by touching the sheet-metal chassis
before  touching an ESD-sensitive part.
Protect the ESD-sensitive parts by placing them in ESD pouches when they are out of the product.
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