HP 4 Plus Manual

							PC (Tray 2) and LC (Tray 3) Tray Size Sensing
System
Trays inserted into the printer trigger specific microswitches,
which define the tray size (see Table 5-4). Refer to Figure 7-1 for
location.    
SwitchDescription PCA
SW601 Door Open Sensing Switches (front and rear) Paper Control PCA
SW602 Test Print Switch Paper Control PCA
SW603 PC tray (Tray 2) Size Sensing Switches Paper Control PCA
SW604 PC tray (Tray 2) Size Sensing Switches Paper Control PCA
SW605 PC tray (Tray 2) Size Sensing Switches Paper Control PCA
SW851 Lower Cassette (Tray 3) Size Sensing Switches Lower Cassette
SW852 Lower Cassette (Tray 3) Size Sensing Switches Lower Cassette
SW853 Lower Cassette (Tray 3) Size Sensing Switches Lower Cassette
Table 5-3Microswitch Signals
Tray SizeSW603
(Upper) SW604
(Middle) SW605
(Lower)
Letter ONOFF ON 
Legal ONONOFF 
A4 OFFOFF ON 
Executive OFFONON 
Tray Not Installed OFFOFFOFF 
Table 5-4Switch Settings for PC (Tray 2) and LC (Tray 3)
Trays
Functional Overview  5-9 
						

							Motors       
The DC Controller controls the Exhaust Fan, the Main Motor,
and the Laser/Scanner Motor. The remaining motors and
solenoids are controlled by State Machines on the motor’s
assembly. The condition of these motors and solenoids is
monitored by the DC Controller through serial data lines.  
The Main Motor (M1) rotates after any printer door is opened and
closed, during the Warm-up period, the Initial Rotation period,
the Print period, or the Last Rotation Period. The Scanner Motor
(M5) is controlled and monitored by the DC Controller PCA. M5
operates during the Initial Rotation period, the Print period, and
the Last Rotation period.
The Paper Feed Assembly Drive Motor (M2) runs during the
Print Period. This motor provides the drive to pick paper from the
PC tray, and deliver it to the Input/Registration Sensor (PS1).
The LC Assembly Motor (M3) provides the drive to pick paper
from the optional 500-sheet Lower Cassette, and deliver it to the
Input/Registration Sensor (PS1). M3 is mounted on the 500-sheet
Lower Cassette. The Envelope Feeder Drive Motor (M4) provides
the drive to pick envelopes from the envelope feeder and deliver
them to the Input/Registration Sensor (PS1). M4 is mounted on
the optional Envelope Feeder.
The Exhaust Fan Motor (FM1) is controlled and monitored by the
DC Controller PCA. The Exhaust Fan Motor operates at
low-speed during the Warm-up period, Standby period, and
during PowerSave. It operates at high-speed during the Initial
Rotation period, the Print period, and the Last Rotation period.
The Paper Feed Assembly Motor (M2) is controlled by the Paper
Control PCA. The Paper Feed Assembly Motor drives the pickup
rollers through SL1 and SL2. These rollers pick media from
either the PC tray (Tray 2) or the MP tray (Tray 1), and deliver
the media to the Paper Registration Sensor (PS1).       
5-10 Functional Overview 
						

							Paper Jam Detection 
The Input/Registration Sensor (PS1) and the Paper Exit Sensor
(PS3) detect paper moving through the printer. If a paper jam is
detected, the DC Controller PCA immediately stops the printing
process and 13 PAPER JA\b  or RE\bOVE PAPER JA\b  message is
displayed. A paper jam can be detected under any of the following
conditions:
•Input Paper Delay Jam:   When paper does not reach the
Input  Paper Sensor (PS1) within the required time.
•Input Paper Stationary Jam:   When paper does not clear
the Input Paper Sensor (PS1) within a specified time.
•Paper Exit Delay Jam:  When paper does not  reach the
Paper Exit Sensor (PS3) within the required time.
•Paper Exit Stationary Jam:   When paper does not clear
the Paper Exit Sensor (PS3) within a specified time.
•False Paper Jam:  If the Rear Door is open, a paper jam
message is displayed because PS3 senses a jam.
Note A defective PS5 (Paper End Sensor) can also
cause a paper jam when paper is fed from the MP
Tray (Tray 1).
Motors
Description
M1 Main Motor (Gear Train Drive Motor)
M2 Paper Input Assembly Drive Motor
M3 500-sheet Lower Cassette Pickup Motor
M4 Envelope Feeder Drive Motor
M5 Scanner Motor
FM1 Exhaust Fan Motor
Table 5-5Motors
Functional Overview  5-11 
						

							Formatter System   
The formatter is responsible for the following:
•Receiving and processing ASCII data from printer interfaces.
•Monitoring front panel input and relaying printer status
information (through the front panel and bi-directional I/O).
•Developing/coordinating data placement and timing with the
print engine.
•Storing font information.
•Communicating with the host computer.
The Formatter PCA can be divided into three functional areas:
•I/O Control
•Memory/Memory Management
•Data Processing
Formatter Feature LaserJet 4LaserJet 4+ LaserJet 5
Processor 20 MHz 80960KA 25 MHz 80960KB 33 MHz 80960JF
REt YesYesYes
MEt NoYesYes
Economode NoYes Yes
Configurable I/O Buffer Size No YesYes
Personality Resource
Saving No
Yes Yes
PowerSave Mode NoYes Yes
Font Cartridge Slot Yes YesNo
MIO Interface Level 5.0  5.16.0
Serial Ports RS-232/422RS-232RS-232 & SIR
Parallel Port Bitronics IEEE-1284 Bitronics  IEEE-1284 Bitronics 
Maximum RAM (PCL/PS) 34/22 MB 66/50 MB66/52 MB
SIMM Support RAM/ROMRAM/ROMRAM/ROM/Flash
PCL Level 55E 6
On-Board Fonts 35 Intellifont/10 TT 
Line Printer 35 Intellifont/10 TT
Line Printer 45 TT & Dark Courier
Line Printer 
Default Symbol Set Roman-8 Roman-8PC-8
Paper Size Support Letter/Legal/A4/Exec Letter/Legal/A4/Exec Letter/Legal/A4/Exec/A5
MP (Tray 1) Modes First,  Manual, Cassette First, Manual, Cassette First,  Cassette
Grayscale Hardware Assist No NoYes
ROPS 3 Hardware Assist No NoYes
Intuitive Control Panel No NoYes
I/O Control
The formatter I/O control is responsible for maintaining
communications with the host system(s). The printer has three
interfaces; serial, parallel (bitronic), and Modular I/O (MIO). The
formatter maintains connections with hosts connected to these
I/O’s including accepting data handshaking, and returning status.
5-12 Functional Overview 
						

							Figure 5-5 Formatter PCA—Functional Areas
Functional Overview  5-13 
						

							Memory Management
The printer uses several different types of memory. This memory
can be divided into two different categories, Read Only Memory
(ROM) and Random Access Memory (RAM). ROM memory
consists of the  memory located on the Formatter PCA and any
font cartridges that may be installed in the printer. RAM memory
consists of RAM memory resident on the Formatter PCA, SIMM
memory installed in the printer, and the Non-Volatile Memory
(NVRAM) located on the Formatter PCA.
In general, the ROM is responsible for storing the instructions for
the operation of the processor and font information.  The RAM
memory is used to store temporary information that will be used
by the printer for a particular print job or a series of print jobs.
This could consist of soft fonts, macros or graphics patterns. RAM
memory is also used by the printer to store data that is being
processed into the raster image that will control the laser and
create the printed page.
The NVRAM is used to store printer configuration information
that can be input from the printer front panel. This information
stored in NVRAM will remain resident in the printer even if the
power to the printer is turned off.
Data Processing
The formatter CPU is responsible for the overall control of all
functions related to the formatter. One of the CPU’s main
functions is to maintain communication with the print engine.
This is done by the print engine interface and the DC Controller
PCA. The DC Controller PCA monitors all print engine functions
such as fuser temperature and paper jam status. The print engine
status is communicated by the DC Controller to the formatter
CPU by the print engine interface. The CPU also controls the
process that converts ASCII data received from the host into the
raster data. This raster data is sent to the laser scanner assembly
via the DC Controller.
Finally the CPU comunicates printer status to the user through
the control panel via the front panel interface. The front panel
interface also transmits front panel inputs to the CPU. 
5-14 Functional Overview 
						

							PJL Overview 
Printer Job Language (PJL) is an integral part of configuration,
in addition to the standard Printer Command Language. With
standard I/O cabling, PJL allows the printer to perform functions
such as:
•Allowing the printer to talk to the host computer through a
Bi-directional parallel connection. The printer can tell the host
such things as the control panel settings, and allow the control
panel settings to be set from the host.
•Dynamic I/O switching allows the printer to be configured
with a host on each I/O. The printer can receive data from any
I/O simultaneously.  
•Context-sensitive switching allows the printer to recognize
automatically the personalities (PostScript or PCL) of each
host and configure itself to serve that personality.
•PJL can act as a spooler to print only sections of a print job as
defined from the software.
•PJL allows any print job to be protected from the effects of the
previous print job. If a print job is sent to the printer in
landscape mode, the subsequent print jobs print in landscape
only if they are formatted for landscape printing.
Functional Overview  5-15 
						

							Image Formation System
Laser printing requires the interaction of several different
technologies (such as electronics, optics, and
electro-photographics) to provide a printed page. Each process
functions independently and must be coordinated with all other
printer processes. The image formation process centers around
the photosensitive drum and consists of six stages:
1. Cleaning 4. Developing
2. Conditioning 5. Transferring
3. Writing 6. Fusing
The toner cartridge houses the cleaning, conditioning, and
developing stages of the electro-photographic (EP) process.
Components of the image formation system that wear, degrade,
or are consumed are built into the replaceable cartridge. The
toner cartridge contains the photosensitive drum, primary
charging roller, developing station, toner cavity, and cleaning
station. This eliminates the need for a service call when
replacement is required.
Figure 5-6 Image Formation System 
5-16 Functional Overview 
						

							Photosensitive Drum 
The photosensitive drum is the “heart” of the Image Formation
System. The special properties of this drum allow an image to be
formed on the drum ’s surface and then transferred to paper. The
drum is an extruded aluminum cylinder. The outside of the
cylinder is coated with a layer of organic-photoconductive
material (OPC) which is non-toxic. The aluminum base of the
photosensitive drum is electrically connected to ground potential
(see Figure 5-7).
Drum Sensitivity  
The OPC material has properties similar to a photo-resistor. It
becomes electrically conductive when exposed to light. When the
photosensitive drum is exposed to light, the negative charges
deposited on it are conducted to the ground potential of the
drum ’s base. Areas not exposed to light remain nonconductive
and maintain their negative charge.
Caution Do not expose the Toner Cartridge to any bright
light source. Too much light permanently
damages the drum.
Figure 5-7 Photosensitive Drum
Functional Overview  5-17 
						

							Cleaning Stage  
During the cleaning stage of the image formation process, the
drum’s surface is physically cleaned, preparing it to hold an
image. During printing, the drum is rotating constantly making
several complete rotations per printed page. Before forming the
image for a given section of print, a cleaning blade removes toner
from the previous rotation of the drum. The excess toner is stored
in the toner cartridge where it is prevented from being used in
later print jobs. 
Figure 5-8 Drum Cleaning Station
5-18 Functional Overview