HP 4 Plus Manual

							Removing and Replacing the Transfer Roller  
The Transfer Roller is the black sponge-rubber roller located
inside the printer just to the front of the black plastic Paper Feed
Guide (see Figure 4-9). To remove and replace the Transfer
Roller, follow these steps.
NoteDo not handle the new Transfer Roller
unnecessarily.  Oils will build up on the roller and
cause print quality problems.
Figure 4-9 Replacing the Transfer Roller
Preventive Maintenance   4-15 
						

							Removing the Transfer Roller   
1Turn OFF and unplug the printer.
2Open the printer’s top cover.
3Remove the Toner Cartridge.
4Use the hook inside the top cover to remove the Transfer
Roller as follows. Hook the left side of the chrome rod beside
the sponge roller, and lift the roller out.  
5Discard the used roller.
Replacing the Transfer Roller   
1Slide the right end of the new roller (the end without the
gear), onto the right slot. Press the rod into the slot.
2Lower the gear end of the roller into place.   
3Install the toner cartridge.
4Replace the hook tool.
5Close the top cover.
6Plug in the power cord and switch the printer ON.
4-16 Preventive Maintenance  
						

							5
Functional Overview
Introduction
This section of the manual presents a functional overview of the
printers. It provides the Service Representative with an
understanding of the printing process. Refer to the block diagram
of Figure 5-1 to see the relationship of the parts as a whole. 
This chapter discusses the following printer functions:    
•DC Controller System
•Formatter System
•Image Formation System
•Paper Feed System
•Power System
•Basic Sequence of Operation
Functional Overview  5-1 
						

							DC Controller System
The DC Controller PCA is responsible for coordinating all
activities involved in the printing process. The DC Controller
enables the drive circuitry for the laser beam, and coordinates
print data from the Formatter PCA with paper size, laser beam
motion, the high voltage system, fuser temperature, and motors.
The DC Controller also shares machine status information with
the Formatter PCA so that proper diagnostic messages are
displayed on the control panel. 
The DC Controller communicates with the Paper Control PCA,
the High Voltage PCA, the Envelope Feeder, Lower Cassette
Assembly and Duplex Assembly by way of two serial data lines
(SLI and SLO). One line (SLO) is used for sending commands, the
other (SLI) is used for receiving status information from the
selected devices. The amount of toner in the Toner Cartridge also
is monitored indirectly with information on the serial data line.    
   
In summary, the following systems and functions are controlled
and/or monitored by the DC Controller:
•Paper Motion
•Laser and Scanner Drive
•Timing
•Machine Status
•Paper Size and Availability
•High Voltage System
•Fusing Temperature
•Main Motor Drive
•DC Power Supply
•Toner Level
5-2 Functional Overview 
						

							DC Controller Loads
Figure 5-1 DC Controller Loads
Functional Overview  5-3 
						

							Serial Data Communication        
The printer communicates with and controls the Paper Feeder,
the Lower Cassette Assembly, and the Envelope Feeder through
serial data lines SLI and SLO. In addition, the DC Controller
uses information encoded on SLI from the High Voltage
Transformer to monitor the toner level.
Communicating with the various subassemblies of the printer
through serial data lines allows many of the functions of the
processor on the DC Controller to be off-loaded to local State
Machines on the subassemblies. The DC Controller uses data line
SLI to receive status information (such as Ready, or Paper Out)
from the subassemblies. Data line SLO is used to issue
commands or to request status.
The State Machines on the subassemblies operate on a clock
synchronous to the DC Controller processor. The printer serial
data lines use serially encoded data protocol to receive and send
information.  
Figure 5-2 Serial Data Flow
5-4 Functional Overview 
						

							Solenoids      
Solenoids are controlled by the DC Controller.  Each solenoid
drives a specific roller (see Table 5-1). The DC Controller outputs
+24B VDC to energize the solenoids at the proper time. When
either of the doors are open, the +24B VDC is removed and the
solenoids are disabled.     
SolenoidDescription PCA
SL1 PC tray (Tray 2) Pickup
Roller Clutch Solenoid Paper Control PCA (J704) 
SL2 Multi-purpose (MP) Tray
(Tray 1)  Pickup Roller
Clutch Solenoid Paper Control PCA (J702)
SL3 Lower Cassette (LC or 
Tray 3)  Pickup Roller
Clutch Solenoid Lower Cassette (J853)
located in Lower Cassette
Drive Assembly. See
Chapter 8 for location.
Table 5-1Solenoid Signals
Figure 5-3 Printer Solenoid and Photosensor Locations
Functional Overview  5-5 
						

							Photosensors    
Photosensors, monitored by the DC Controller, are responsible for
detecting the presence of paper, paper motion, and timing. (See
Table 5-2.) Photosensor PS2 senses paper in the PC tray;
photosensor PS4 senses paper in the MP tray. The message PC
LOAD  or \bP LOAD  is displayed when either the PC tray or the MP
tray is selected as the primary tray and is out of paper. PS6 and
PS7 (respectively) sense the presence of paper in the Lower
Cassette and the Envelope Feeder. Paper must be loaded into the
primary paper tray before printing can resume. The message  PC
E\bPTY  or \bP E\bPTY  is displayed when either the PC tray or the
MP tray is out of paper and is not selected as the primary paper
tray.  LC E\bPTY  or EE E\bPTY  is displayed when the Lower Cassette
or the Envelope Feeder is empty. The  E\bPTY message is only a
reminder that the paper tray is empty; it is not necessary to load
paper to continue printing from another tray. 
The Paper Control PCA, Lower Cassette Assembly, and the
Envelope Feeder communicate with the DC Controller through
serial data lines. The condition of  the printer engine
photosensors  PS2, PS4, PS5, the optional Lower Cassette PS6,
and the optional Envelope Feeder PS7 is encoded into a digital
logic stream and read by the DC Controller on line SLI.
PS1 detects paper at the Input Feed Roller and is used in jam
detection and registration. PS3 detects the presence of paper in
the Fuser Assembly, and is used in jam detection. PS5 terminates
laser operation when it detects the end of the sheet.  This allows
the printer to print images on odd-sized media fed from the MP
tray without contaminating the Transfer Roller.
Note The LaserJet 5 printer uses different tray
designators and associated messages as follows.
LJ 4 / 4 Plus
LJ 5
M P  Tr a y Tr a y   1
P C  Tr a y Tr a y   2
L C  Tr a y Tr a y   3
\bP\fPC\fLC LOAD TRAY x LOAD (x=1,2, or 3)
\bP\fPC\fLC E\bPTY TRAY x E\bPTY (x=1,2, or 3)
5-6 Functional Overview 
						

							SensorDescription PCA
PS1 Input/Registration Sensor - detects paper in
pickup area Paper Control
PCA (J605)
PS2 PC tray (Tray 2) Paper-out Sensor - detects the presence of paper in the PC tray. Paper Control
PCA (J605)
PS3 Output/Fuser Exit Sensor - detects paper in fuser. DC Controller
(J208)
PS4 MP Tray (Tray 1) Paper Out Sensor - detects the presence of paper in the MP tray (Tray 1). Paper Control
PCA (J701)
PS5 MP Tray (Tray 1) paper end - detects the trailing edge of paper fed from the MP tray (Tray 1). Sensor PCA
(J702)
PS6 Optional Lower Cassette (LC or Tray 3) Paper-out Sensor - detects the presence of
paper in the 500-sheet feeder. See Chapter 8
for location. Paper Control
PCA (J603)
PS7 Optional Envelope Feeder Paper-out Sensor - detects the presence of paper in the envelope
feeder. See Chapter 8 for location. Paper Control
PCA (J604)
Table 5-2Photosensor Signals
Figure 5-4 Photosensor Locations
Functional Overview  5-7 
						

							Microswitches         
All microswitch conditions are monitored by the DC Controller
over serial data lines SLI and SLO. The State Machines on the
individual control PCAs, (for example the Paper Control PCA)
convert the switch condition to a digital logic level, and encode
that information on the data stream for the DC Controller to use.
SW601 (Door Open Sensing switch) monitors the top cover.  If the
top cover is open, the printing process stops and the  12
PRINTER OPEN  message is displayed.  SW601 disables the +24V
(B) voltage, so the printer goes through the warm-up cycle after
the cover is closed.
SW602  (Test Print switch) is labeled and located under the MP
tray (Tray 1) door on the right edge of the door opening. The Print
Engine Test isolates the entire printer from the Formatter PCA.
Press the Test Print switch once to start the Print Engine Test.
The Print Engine Test is a good method for finding whether print
problems are associated with the DC Controller or the Formatter
PCA.  
Paper tray size microswitches are activated by protrusions on
each PC tray (Tray 2). The tray size is determined by the
combination of engaged microswitches (see Table 5-3 and 5-4).  
SW 603, 604, 605  (Cassette Size Switches) are for the PC tray
(Tray 2), and  SW 851, 852, 853  are for the 500-sheet Lower
Cassette (Tray 3). These microswitches work together to indicate
to the DC Controller which size cassette is installed, or indicate
that the cassette is incorrectly installed. The combinations for
each cassette size are listed in Table 5-4.
5-8 Functional Overview