HP Laserjet 4 Manual

Electrical Overview
The block diagram in Figure A-3 shows the Duplexer electrical
components.
AC  PO WE R
SUPPLY
DUPLEXER
CONTROL
PC A AC  PO WE R
TO  PR I N TE R
INPUT
AC  PO WE R
TO  PR I N TE R
DC CONTROLLERFAN
SWITCHBACK
SOLENOID
SWITCHBACK
STEPPER MOTOR
HOLDING TRAY
STEPPER MOTOR
SWITCHBACK
PAPER SENSOR
HOLDING TRAY
PAPER SENSOR
Figure A-3 Electrical Block Diagram
Duplexer   A -5 

Installing the Optional Duplexer
The optional Duplexer can be installed by the customer. There
are no fasteners securing the units together.  The printer simply
rests in place on top of the Duplexer, which, in turn, rests on top
of the optional 500-sheet Lower Cassette, if used.  
To install the Duplexer, first turn power OFF and disconnect all
cables from the printer.  Follow the steps below, referring to the
corresponding steps illustrated in Figure A-4. 
•Open the printer’s rear door and use...

7
6
52
4 3
1
23
1
2
11
2
Figure A-4 Duplexer Installation/Removal
Duplexer   A -7 

Removal and Replacement
This section describes the complete disassembly of the Duplexer.
Tasks that must be performed before beginning the procedure are
listed first. Remove the assemblies in the order listed to prevent
damage.
The assembly procedure is the reverse of the removal procedure,
except where specific instructions are provided.
In the removal and replacement procedures that follow, the
number inside the parentheses, such as (4), refers to the number
of screws to remove.
WarningPower OFF the...

Removing the Covers
Removing the Switchback Covers
1Remove the (2) screws shown in Figure A-5, callout 1. 
2Lift the cover off the Switchback Assembly.
Figure A-5 Switchback Cover
Duplexer   A -9 

Removing the Side Cover on Power Side
1Open the front door.
2Remove the (1) screw shown in Figure A-6, callout 1.
3Release the (3) latch points with a flat screwdriver and rotate
the cover downward (see Figure A-6, callout 2).
Figure A-6 Side Cover
A -10  Duplexer  

Removing the Side Cover on Gear Side
1Remove the (2) screws on top and the (1) screw on the front
(see Figure A-7, callout 1).
2Turn the Duplexer on its side to access the latch location on
the underside.
3Release the (1) latch point with a flat screwdriver and lift the
cover off (see Figure A-8).
Figure A-7 Side Cover on Gear Side
Duplexer   A -11 

Figure A-8 Latch Location on Underside of Duplexer
A -12  Duplexer  

Removing the Back Cover
1Place the duplexer on a table or bench so that the back
overhangs the edge by a few inches.
2Release the (2) locating pins as shown in Figure A-9.
3Rotate the cover downward until it is free.
Removing the Front Cover
With the side covers removed, the front cover is only attached by
the holding tray arm.
1With both side covers removed, open the holding tray.
2Rotate the front cover 90 degrees to release the holding tray
arm.
Figure A-9 Back Cover
Duplexer   A -13 

Removing Internal Duplexer Components
Removing the Fan/Motor/Solenoid/Sensor
Access to the electronic components of the switchback assembly is
easy once the covers are removed.  Note the location of the
switchback stepper motor (Figure A-10, callout 1), the switchback
fan assembly (callout 2) and the switchback solenoid (callout 3).
Figure A-10 Switchback Assembly - Stepper Motor Side
A -14  Duplexer