HP 4 Plus Manual

							Printing from the MP Tray (Tray 1) 
MP tray selection is provided by the Formatter PCA, as
configured by the operator’s control panel or by a software
application. The MP tray (Tray 1) feed system ’s paper motion
begins when the DC Controller PCA, after receiving a 
PRNT
signal, starts the Scanner Motor (M5) and the Main Motor (M1).
When the fusing roller reaches the minimum operating
temperature (183 ° C), the MP pickup roller clutch solenoid (SL2)
is energized for 1 second, allowing the MP pickup roller to make
one rotation. Clutches and solenoids work together to start and
stop gears and rollers used for paper movement. The MP pickup
roller then feeds a sheet of paper from the MP tray (Tray 1).
The Formatter PCA sends the 
VDO signal to the print engine
within a specific time period after the paper reaches the
Input/Registration Paper Sensor (PS1).  This aligns the leading
edge of the toner image on the photosensitive drum with the
leading edge of the paper. After the paper passes the drum and
the fusing rollers, it triggers the Paper Exit Sensor (PS3). The
paper then is directed to the output tray. 
If the paper does not reach or clear each sensor within a specified
time, the microprocessor on the DC Controller PCA assumes a
paper jam occurred and informs the Formatter PCA.
Figure 5-18 MP Tray (Tray 1) to Output Tray Paper Path
Functional Overview  5-29 
						

							Printing from the PC Tray (Tray 2)  
PC tray selection is provided by the Formatter PCA, as
configured by the control panel or by software. When the DC
Controller PCA receives a 
PRNT signal, it starts the Scanner
Motor (M5) and the Main Motor (M1). When the fusing roller
reaches the minimum operating temperature (approximately 183 °
C), the PC tray (Tray 2) pickup roller clutch solenoid (SL1) is
energized for 1 second, allowing the roller to make one rotation.
The PC tray pickup roller then feeds a sheet of paper from the PC
tray into the PC tray input feed rollers. The PC tray input feed
rollers turn until paper reaches the Input/Registration Sensor
(PS1).  When the media is sensed at (PS1), the pickup motor (M2)
stops and the paper is carried through the remainder of the print
path by the Main Motor (M1).
The Formatter PCA sends the 
VDO signal to the print engine
after the paper reaches the Input Paper Sensor (PS1). This aligns
the leading edge of the toner image on the photosensitive drum
with the leading edge of the paper. After the paper passes the
drum and the fusing rollers, it triggers the Paper Exit Sensor
(PS3). The paper is then fed into the output tray.
If the paper does not reach or clear each sensor within a specified
time, the microprocessor on the DC Controller PCA assumes a
paper jam occurred and informs the Formatter PCA.
Figure 5-19 PC Tray (Tray 2) and LC Tray (Tray 3) to Output Tray Paper Path
5-30 Functional Overview 
						

							Po w e r  S y s t e m  
When the main power switch is turned ON, the AC Power Supply
provides AC voltage to the DC Power Supply and the fuser
assembly heat lamp. The paper path doors must be closed to
activate the AC power supply door switches before voltage is
provided to the heat lamp.  
The DC Power Supply generates +5V DC, and +24V DC for use
by the Formatter PCA and the DC Controller PCA. The DC
Controller PCA distributes voltages to the remaining electrical
assemblies. Over-current protection for the DC Power Supply is
provided by a current monitoring circuit (crowbar circuit). To
reset the crowbar circuit, the printer’s power must be turned OFF
for at least ten minutes. The power system block diagram is
illustrated in Figure 5-20.
Note that both AC and DC power supplies are contained within
the Power Supply Assembly. The high voltage power supply is a
discrete assembly located on the underside of the printer.
Functional Overview  5-31 
						

							Figure 5-20 Power System Block Diagram
5-32 Functional Overview 
						

							Basic Sequence of Operation  
The Formatter PCA and the DC Controller PCA share
information during printer operation. Connector J7 on the
formatter and connector J207 on the DC controller form a link
which operates as a serial data bus. This allows printer status,
command information, and dot-image data to be passed between
both controllers.
Standard Printer Operation  
The following events take place during normal printer operation:
1After the printer’s power is turned ON, the printer enters the
Warmup period.
2After the printer completes the Warmup period and is ready
for operation, the DC controller sends a READY signal (
RDY)
to the formatter.
3After the RDY signal is true and print data is ready to be
transmitted, the formatter sends a PRINT signal (
PRNT) to
the DC controller.
4After the DC controller receives the PRNT  signal, the Initial
Rotation period begins.
5At the end of the Initial Rotation period, the DC controller
sends a TOP OF PRINT signal (
TOP) synchronized with a
BEAM DETECT signal (
BD) to the formatter. This initiates
the Print period.
Functional Overview  5-33 
						

							6Each time the formatter receives a synchronized BD signal
from the DC controller, the formatter sends a VIDEO data
stream (
VDO) to the DC controller.
7After the DC controller receives the VDO data, the DC
controller translates it into a VIDEO OUT signal (
VDOUT)
that switches the laser diode ON and OFF.
8The laser beam, created by the laser diode, reflects off the
scanner mirror onto the photosensitive drum to form a latent
electrostatic image, writing a single line of print (dot) data.
9After the last VDO line of dot data is sent from the formatter,
the DC controller checks for another 
PRNT  signal from the
formatter.
10If another PRNT  signal is detected, the Print period continues
with another page.
11If the DC controller fails to receive a PRNT  signal before the
end of the page passes over the Input/Registration Sensor
(PS1), the DC controller initiates the Last Rotation period.
If the printer fails to perform correctly, the DC controller sends
an appropriate status to the formatter PCA, and an error is
displayed on the printer ’s control panel.
Timing Diagrams 
The following timing diagram describes the operation of the
printers. The  “MP Tray Timing Diagram ” was developed by
running two consecutive prints on A4 paper.
5-34 Functional Overview 
						

							This a 2 panel pull-out.
Figure 5-21 MP Tray Timing Diagram —HP LaserJet 4/4M
Functional Overview  5-35 
						

							This a 2 panel pull-out.
Figure 5-22 MP  (Tray 1) Timing Diagram —HP LaserJet 4
Plus/4M Plus/5/5M/5N
5-36 Functional Overview 
						

							Warmup Period  
The Warmup period begins when the printer’s power is turned
ON, and ends when the fusing roller temperature reaches 172 ° C.
When the printer is switched ON, the exhaust fan (FM1) begins
low-speed rotation and the fusing roller maintains 172 ° C. The
DC controller then switches the main motor (M1) ON, and applies
AC high voltage to the primary charging roller to remove any
residual charge from the photosensitive drum.  Negative high
voltage is applied to the transfer roller to clean toner build-up
from the roller. When the fusing roller reaches 172 ° C, the main
motor, and AC high voltage, are turned OFF.
After the power is switched on, the Main Motor (M1) and the
pickup motor (M2) turn for approximately 4 seconds to clear the
paper path. The motors stop rotation when the fuser reaches 
172 ° C.
After the printer warms up, the message  00 READY is displayed,
the printer goes  “on-line,” and the control panel keys become
operational.
Standby Period  
When the Warmup period is completed, the message  00 READY is
displayed. At this point the printer is in the Standby period. This
indicates that the printer is ready for printing. The fusing roller
remains at a constant temperature of 172 ° C, and the exhaust fan
continues operating at low-speed rotation.
Po w e r S a v e
When the printer enters PowerSave mode, fuser current is shut
down, allowing the fuser to cool to room temperature without
posting a  50 SERVICE  error.  The exhaust fan continues to operate
at low speed.
Functional Overview  5-37 
						

							Initial Rotation Period  
When the DC controller receives a PRINT signal (PRNT) from the
formatter, the DC controller allows the fusing roller to begin
warming up to approximately 183 ° C, and starts the main motor
(M1), the pickup motor (M2), and scanner motor (M5). Next, the
laser diode turns ON and generates a sweep beam used to adjust
the laser power (APCIN). After the DC controller receives a
BEAM DETECT signal (
BD) initiated by the sweep beam, the
laser power stabilizes and the sweep beam turns OFF.
The DC controller then turns ON the main motor, switches the
exhaust fan to high-speed rotation, applies AC high voltage and
negative DC high voltage to the primary charging roller, and
applies negative high voltage to the transfer roller to help remove
excess toner.
The developing bias (a negative AC/DC voltage) is applied to the
developing roller 1.16 seconds after the main motor is turned ON,
then positive high voltage is applied to the transfer roller 2.0
seconds after the main motor is turned ON.
When the fusing roller temperature reaches 183 °, the MP 
(Tray 1) pickup roller clutch solenoid (SL2) energizes and paper is
fed from the tray. If paper feeds from the PC tray (Tray 2),
roughly 10 seconds after Initial Rotation begins, the PC tray
(Tray 2) pickup roller clutch solenoid (SL1) energizes.
5-38 Functional Overview