Chapter 5

Image Formation System 5-22 Photosensitive Drum 5-23 Drum Sensitivity 5-24 Cleaning Stage 5-25 Conditioning Stage 5-26 Writing Stage 5-27 Developing Stage 5-29 Transferring Stage 5-31 Fusing Stage 5-32 Paper Feed System 5-33 Paper Movement Overview 5-34 Solenoids 5-35 Photosensors 5-35 Paper Out Sensor (PS2) 5-35 Input Paper Sensor (PS1) 5-36 Printing from the Paper Cassette 5-37 Manual Feed Printing 5-38 Small Media Rollers (LaserJet 4P/4MP) 5-38 Paper Jam Detection 5-39 Power-On Jams 5-39 Pickup Jams 5-39 Delay Jams 5-39 Basic Sequence of Operation 5-40 Standard Printer Operation 5-40 General Timing Diagram 5-41

Cx-?.apbfckmiw?iNts

JRmmKmd and W@wmnm?nt Removal and Replacement Required Tools 6-3 User Installable Assemblies 6-4 Memory Upgrade (LaserJet 4L) 6-4 Memory/Language SIMMS (LaserJet 4P/4MP) 6-5 Cover and Doors 6-6 Power, I/O and Memory Printer Cover (LaserJet Printer Cover (LaserJet Rear Door 6-12 Control Panel (LaserJet Doors (LaserJet 41J4ML) -6-6 4L/4ML) -6-7 4P/4MP) -6-9 4P/4MP) ~ 6-13 Strategy 6-2
Left Side Assemblies 6-15 Formatter Shield and PCA 6-15 Gear Train Assembly 6-17 Main Motor 6-19 Front Assemblies 6-20 Front Oblique Roller Assembly 6-20 Paper Cassette Assembly 6-21 Tray Forms Size Guide (LaserJet 4L/4ML) -6-21 Compression Springs 6-22 Internal Assemblies 6-23 Laser/Scanner Assembly 6-23 Fan 6-24 Power Switch Assembly (LaserJet 4P/4MP only) -6-25 Paper Guide/Top Oblique Roller Assembly 6-26 Transfer Roller and Guide 6-27 Transfer Roller Bushings 6-Beam-to-Drum Mirror Assembly 6-29

(continued on back)

Chapter 6
Rear Assemblies 6-30 Fusing Assembly 6-30 Fusing Assembly Components 6-31 Pressure Plate 6-31 Upper Fusing Assembly (Teflon Sleeve and Heater Element) -6-32 Pressure Roller 6-33 Delivery Assembly 6-33 Lower Delivery Roller 6-34 Lower Delivery GuidelExit Sensor Flag 6-35 Connector Assembly (Fuser Entrance Guide) 6-36 Upper Output Roller Assembly 6-37 Lower Output Rollers 6-38 Bottom Assemblies 6-39 DC Controller Assembly 6-39 Pickup Solenoid (SL2) 6-41 DC Controller Fuses 6-42 High Voltage Connector Assembly 6-42 DC Controller PCA 6-43 Pickup Feed D-Roller 6-46 Pickup Assembly 6-47 Feeder Guide Assembly and High Voltage Shield 6-49 Small Media Roller Assembly (LaserJet 4P/4MP) -6-50 Static Eliminator Strip Assembly 6-51 Toner Cartridge Lever Assembly 6-52 Top Door Switch (Plunger Assembly) 6-53 DC Controller/Scanner Connector Assembly -6-54 PS1 Input Paper Sensor Arm 6-56
. TmlldMeshmtintg Troubleshooting

Flowchart 7-2 7-4

Paper Path and Components DC Controller Diagram 7-5
Printer Error Troubleshooting 7-6 LaserJet 4L/4ML: 7-6 LaserJet 4P/4MP: 7-6 Priority of Errors 7-7 Recoverable Errors 7-7 Service Errors 7-11 LaserJet 4L/4ML 7-11 LaserJet 4P/4MP 7-11 Clearable Warnings (LaserJet 4P/4MP) 7-18 Image Formation Troubleshooting 7-19 Engine Test 7-36 Engine Test Button Location 7-36 Printing an Engine Test - LaserJet 4L/4ML 7-36 Printing an Engine Test - LaserJet 4P/4MP 7-37 Half Self Test Functional Drum Rotation Functional High-Voltage Paper Curl 7-42 Adjustment Procedures 7-43 Leading Edge Adjustment 7-43 Beam-to-Drum Mirror Adjustment 7-44 Troubleshooting Tools 7-46 Repetitive Image Defect Ruler 7-46 Main Wiring Diagram 7-47 Check 7-39 Check 7-40

RESULT Prints a Self Test page,
All lights cycle Prints continuous self tesi through. Release pages. Press the button button when DATA to stop printing. light only is on (4ML: all lights on). Always available except when all lights are lit (Service Error). Clears all data from memory, including unprinted data, downloaded fonts and macros, Resets printer to factory default settings. Takes the printer out of Intelligent Off mode. Allows the printer to recover and continue printing the iob. Print remaining data in printer memory. Override manual feed to print from paper cassette.

Continue

Wake Up Form Feed Manual Override Service Error Codes
Press button for two seconds. Press button for two seconds, Press button for two seconds, Press button for two seconds. Hold down button to display code.
All off. Any recoverable error code (see Chapter 7). DATA and READY light on steady, DATA light blinking.
All lights on steady. Press the button to display service light pattern. Use Chapter 7 to determine the problem and solution.
Installation and Configuration Using the Control F%nei
LaserJet 4P/4MP Control Panel Overview
The HP LaserJet 4P/4MP printers front control ~anel consists of a 16 character backlit LCD display, an 8 key contr;l panel, and 4 LED status lights situated on top of the printer. To access a primary key function (such as On Line, Form Feed, or Menu) just press the appropriate key. To access secondary key functions (Reset, EconoMode and -), use the_ key. For example, to access the reset function of the ~ key, press _ and ~ simultaneously.

igure 3-3

LaserJet 41Y4MP Front Control
Installation and Configuration using it%?Cmml
LaserJet 4P/4MP Control Panel Display and Lights The printers control panel has a 16 character backlit LCD message display area and four LED status indicator lights. A complete list of display panel messages is in Chapter 7. The following describes the functions of the four lights. Ready Light ON STEADY: There are no error conditions detected. The printer can only receive a print job when this light as well as the On Line light are on. BLINKING: The printer is receiving or processing data. Do not take off line or switch power off until the light stops blinking. OFF: The printer is not ready to print. Check the display panel for a message.

On fine

The other Service Menu items, z::! 2;?!H=: and ~:I:w%:3T I>;= are included for specialized purposes. If either item needs to be changed from the default setting (=%.: and :H%, respectively), s;: the procedure is similar to that used for setting the page count or Cold Reset default, described above.

Printing a Self Test

LaserJet 4L/4ML:
1, Make sure the Ready light is on, and all other lights are off. (If necessary, reset the printer. ) 2. Briefly press the front panel button (LaserJet 4ML, see Note below). 3. After about 6 seconds, the Data light blinks and the self test page starts to print (see Figure 3-6). Usually, only one page prints. If fonts or macros have been downloaded, a second page prints. LaserJet 4Mh The procedure above prints a demo page only on the LaserJet 4ML. To print PCL and PostScript configuration pages on the LaserJet 4ML, press and hold the front panel button down for at least 10 seconds, until the Data light is ON and the Ready light is blinking. Five pages will be printed (including font sample pages).

,,,.:, :*>

LaserJet 4P/4MP:
to take the printer offline. The On Line light 1. Press goes off and the display reads H CFT%.:i?i-. a 2. Press 3. Press m repeatedly until T:+T !+%:.: s displayed. i
to display :+KL.F [::~-~.
The display panel reads {;:! ~;;i.~ ;>;;T. After a 4. Press ~. few minutes a PCL Configuration self test page is printed (see Figure 3-7).
installation and Configuration Printing a %4$ Tesi
Figure 3-6 shows a self test printout for the LaserJet 4L. It lists al~factory default settings.

26 Scalable

Typefaces
Courier Courier courier Courier ad It Bd It

b******@**

Letter Gothic Letter W.hi c Bd Letter Goth]c !t CG Times CG llmes Bd
CG ?hes it CG ZWnesEd h CJ.A
Univms Ed Un;vers Md It Unfwers 8d M Uuiws Md Cd Umiwm Ed Cd

Umim MdCd,i Utivets M Wh

m ****8****

EconoMode HP Explorer

Univers tvld
Af)tlCme Ohre Aatiaue Olive Bd Antkwe Olive It Albems Md Albertus XBd Wingdng3 rsd%l%~%c

LmR.4m Ehhanced PCL 5

W L!3TBR OFF Mmmn.i LTo AUIO OFF OFF 12.0 10.0 EO!.(AN8

3 &

Bi-Tronics * Ii!!51

RAM s;,.

POW,* P.9gc Cmmk F)rmvm, Datcmdc : IWO Adapt Uti COtml Errors

,~~~ o

15520927 No None

Figure 3-6

LaserJet 4L Self Test Page (showing default settings)
Installation and Configuration Printing a SM Test
The LaserJet 4L Self Test Fields
1. Printer Features List. This area can be used to check for graphics print quality. 2. Scalable Typeface List. Samples of the printers internal scalable typefaces. hlaa

Removing

to facto~-default
ac power returns items 3 through 12 settings (shown in Figure 3-6).

3. Paper Handling.

Shows the current paper settings. Current settings for print density (REt).

Power System (on DC Controller
The ac, dc and high voltage power supply circuits are all contained within the DC Controller PCA. AC Power Distribution The ac power circuitry, located on the DC Controller PCA, supplies ac voltage to the DC Power Supply whenever the printers power cord is connected to the ac power source. (The power switch must be turned ON in the LaserJet 4P/4MP.) A toner cartridge must be installed and the top door closed before voltage is supplied to the High Voltage Power Supply or Main Motor drive circuitry. DC Power Distribution The DC Power Supply circuitry, located on the DC Controller PCA, generates +5 V dc, and +12 V dc, which is used as follows: +5 V dc: Formatter PCA Photosensors DC Controller Circuitry Laser/Scanner Assembly High Voltage Power Supply Main Motor Solenoids Laser/Scanner
+12a V dc: (a=after switch) +12b V dc: (b=before switch)

Assembly

(to Fan) in Figure 5-4.
The Power System Block Diagram is illustrated

supply r ---,

Main switch

I II*1 ----

SW201 [4P/4MP Only)

~ Fuse

(FU201)
: H]gh- : SW201 T, +12av 1 uOlta9e \ ; power ; -k : t :.circul.,.

Fusing Heeter

filter
Overvoltage/ Iovercurrent detection circuit

Regula!or

f+12bV

Door switch

power supply circuil
12b V=Voltage before switch 12a V=Voltage after switch,

Mainmotor

sub supply oower circuii ----.-i
. !~ Main : momr dflve ; drcuit +12a V K

d Solanoid I

Figure 5.4

m -----w F--I +5V

Fan motor

+5!!!!

Formetter PCA

morvionmg input

Power Supply Block Diagram
Overcurrent/Overvoltage Protection The +12V dc and +5V dc power circuits each contain an overcurrent/overvoltage protection circuit which automatically shuts off the output voltage when an overcurrent condition occurs due to a short or abnormal voltage on the load side. The protection circuit automatically resets after the input power is cycled OFF then ON. Fuse FU101 provides overcurrent protection for the Fusing System circuitry. Fuse FU201 (not present on 220-240 V units) provides protection in case of a catastrophic overcurrent condition in the DC Controller power supply regulation circuitry. Intelligent ON/OFF (LaserJet 4L/4ML only)
This printer feature conserves power by shutting down all the printers front panel LED status lights after a 15 minute period of inactivity. The printer retains all printer settings and downloaded fonts and macros while in Intelligent Off mode. The lights power ON instantly when any of the following occur: e A file is printed. @ The front panel button is pressed. The printers top door is opened.

$?jJ--J

Figure 6-24
Removing the Paper Guide/Roller Assembly
Tore-install: Ensure that the Guide Assembly is under the top door release button plunger and that the two tabs are in place.
Removal and Replacement internal Assemblies
Transfer Roller and Guide a
The Transfer Roller is located inside the top door, under the toner cartridge. The Printer Cover does not need to be removed to replace the Transfer Roller. Do not touch or otherwise contaminate the surface of the Transfer Roller. Skin oils and other contaminants affect its electrical characteristics, resulting in poor image transfer.
1. Open the top door and remove the toner cartridge. 2. Using a flat-blade screwdriver, gently pry under the left end to lift the roller shaft upward (Figure 6-25, callout 1).

Figure 6-25

Replacing Me Transfer Roller
3. Lift the Transfer Roller and Guide slightly and slide toward the left to remove. Do not lift the roller more than about 1 inch (2.5 cm) before sliding it out of the right bushing. 4. Pull the Roller shaft out of the clips on the Transfer Roller Guide to release the Transfer Roller from the Guide. Note If replacing just the Transfer Roller Guide, be careful not to lose the Transfer Roller gear. It is only held in place by slight pressure and can fall off the Roller shaft.
Tore-install: Install the right end first. Ensure that the tabs are seated firmly in place below the plastic guide (Figure 6-25, callout 2), and push the Transfer Roller into place.
Transfer Roller Bushings The Transfer Roller Bushings are located under the left and right ends of the Transfer Roller (refer to Figure 6-25). It is not necessary to remove the Printer Cover to replace the bushings. 1. Open the top door and remove the toner carttidge. 2. Remove the Transfer Roller (Figure 6-25). 3. Remove the (1) self-tapping screw and lift the bushing straight out (the same procedure applies for both the left and right bushings).

internal Assemblies

Beam-to-Drum

Mirror Assembly

Be carefi.d not to touch the surface of the mirror on the underside of the assembly. If the mirror does get contaminated, use filtered, compressed air to clean. If still dirty, clean it carefully using lens cleaner and a lint free cloth or swab.
1. Remove the Printer Cover. 2. Note where the mark on the printer chassis aligns with the graduated scale on the mirror (Figure 6-26, callout 1). 3. Remove the (2) self-tapping screws (Figure 6-26, callout 2). Grasp the mirror assembly by the sides only, and lift to remove.

Figure 6-26

%m=mwng ills Beam.to.lclrum

Mirror

Tore-install: Install in the correct alignment as noted in step 2. Check adjustment according to the Beam-to-Drum Mirror Adjustment procedure in Chapter 7.
Removal and Replacement Rear Assemblies

Rear Assemblies

Fusing Assembly
1. Remove the Printer Cover. 2. Remove the machine screws with star washers (1 on 4LJ4ML, 2 on 4P/4MP) (Figure 6-27, callout 1). 3. Remove the (2) self-tapping 4. screws (Figure 6-27, callout 2).
Slide the Fusing Assembly straight out from the rear of the unit (some resistance may be encountered because of the two connectors to the DC Controller).

) Figure 6-27

Removing the Fusing Assembly (Laser&?t 4P shown)

Components

The following procedure describes the steps for disassembling the Fusing Assembly (after it has been removed from the printer). Please perform the steps in the sequence listed. Pressure Plate CAUTION Do not remove or disturb the (2) stationary compression springs located at either end on top of the pressure plate. Dislocation of these springs can cause poor fusing.
1. Remove the spring from each end of the Pressure Plate (Figure 6-28, call&t 1). 2. Open the Pressure Plate more than 90 degrees and lift it off its
Upper Fusing Assembly (Teflon Sleeve and Heater Element) 1. Unsnap and open the cable clip shown in Figure 6-29, callout 1. 2. Remove the wires from the open cable clip and gently squeeze the connector to unplug. 3. Unplug the second connector shown in Figure 6-29, callout 2. 4. Squeeze the tab on the ceramic heater element connector and pull the connector free (Figure 6-29, callout 3). 5. Grip both ends of the Upper Fusing Assembly, lifting it out.

Figwe 6=29

wing Assembly Rwnoving upper Me

Pressure Roller

The plastic bushings under each end of the Pressure Roller can fall out of place and be easily lost.
1. The Pressure Roller is now free. Grasp both ends and lift it out.
Delivery Assembly 1. Pull out gently on the metal frame on either end of the Delivery Assembly to release the mounting pins. Lift the assembly out (Figure 6-30).

Figure 6-30

Removing the Fuser Delivery Assembly
Tore-install: Ensure that the assembly is installed with its white plastic pressure rollers toward the back of the Fusing Assembly, adjacent to the Lower Delivery Rollers. It is possible to install the Delivery Assembly backwards.
Lower Delivery Roller 1. Lift up on the bushing tab and slide the shaft inward and out of the bushing (Figure 6-31, callout 1). 2. Slide the bushing out from the metal frame and slide the Lower Delivery Roller out (Figure 6-31, callout 2).

Fic.y,mi+ -31 6

H-K? ILcmwDelivery !%lkr
Lower Delivery Guide/Exit

Sensor Flag

1. Slide the Lower Delivery Guide slightly back to clear the center tab and lift the guide out, being careful not to damage the Exit Sensor Flag.

~lca QDI C)m

There is a service error. Press and hold the front panel button to display the error light code. This code will be shown only while the button is pressed, The following tables list possible error codes. NOTE: If no further error code is displayed, yet all four lights remain on continuously, power cycle the printer. If the condition persists, replace the Formatter PCA.

l!wiL-

Table 7-7
Fuser Error LaserJet 4P/4MP Display Panel 50 SERVICE
Ready and Error lights are on and all others are off.

ND fg= C)m SUSPECT.

1. Remove power to the printer for 15 minutes. If this doesnt clear the error: 2. Perform the Fuser Checks shown in the table below. 3. Check the Fuses (FU101 and FU201) on the DC Controller PCA. Replace if faulty. 3. Replace the DC Controller PCA.

Table 7-8

Fuser Checks I CHECK Ensure that J103 and J204 connectors on the Fusing Assembly are seated securely into the DC Controller PCA connectors (see Figure 6-29 in Chapter 6 for locations). Reseat the Fusing Assembly, Remove the Fuser and measure the resistance between connectors J204-1 and J204-2 (see Figure 6-29 in Chapter 6 for location), Resistance should read approximately 440 K Ohms at 20 Deg C (room temperature). If the thermistor wire is open, replace the Fusing Assembly. Measure the continuity between connectors JI 03-1 and J1 03-2 on the Fuser (see Figure 6-29, Chapter 6 for location). It should be approximately 29 Ohms. If the thermal fuse is open, replace the Fusing Assembly

1. Connector Contact

2. Thermistor wire open.

3. Thermal Fuse.

Table 7-9
Beam Error LaserJet 4P/4MP Display. Panel. 51 ERROR
Data and Error lights are on and all others are off.
Elm am UD LaserJet 4L/4ML LEDs ;: Qm
Power-cycle the printer. If this doesnt clear the error: 1. Reseat the Laser/Scanner Assembly into the Scanner/DC Cable Assembly. 2. Replace the Laser/Scanner Assembly. 3. Replace the DC Controller PCA, 4. Replace the Scanner/DC Cable Assembly.

Table 7-1O

Scanner Error LaserJet 4P/4MP Display Panel 52 ERROR Description & Recommendations
D UE3 Paper and Error lights are on and all others are off.
Power-cycle the printer. If this doesnt clear the error: 1, Ensure condensation from moving the printer from a cold to warm environment hasnt occurred, Allow the printer 6 hours to acclimate to the warm room. 2. Reseat the Scanning Assembly. 3. Replace the Laser/Scanner Assembly. 4. Replace the DC Controller PCA, 5. Replace the Scanner/DC Cable Assembly,
Troubleshooting Printer Error Troubleshooting

Table 7-11

RAM/ROM Error LaserJet 4P/4MP Display Panel [XY-ZZ] ERROR
An error has been found in RAM or ROM. 1. Power-cycle the printer. If this doesnt clear the error: 2. Power off the printer, remove any additional memory, then power back on. If the message clears, replace the memory card. 3. Replace the Formatter PCA. LaserJet 4P/4MP: Use the list below to decode the [XY-ZZ] values: X - Hardware type: O = ROM 1. RAM Y- Hardware device: O. On board RAM/ROM. 1 = SIMM slot one. 2 = SIMM slot tWO. 3 = SIMM slot three. ZZ - Error Number: 00= Unsupported memory. 01 = Unrecognized memory. 02= Unsupported memory size 03= Failed RAM test. 04= Exceeded max RAM size. 05= Exceeded max ROM size. 06= Invalid SIMM speed. 07= SIMM reporting incorrect. 08= SIMM RAM parity error.

4, Foreign objects in beam path. Any for-
eign objects will block the light from developing an image on the Photosensitive drum.

Table 7-22

Vertical Black Lines POSSIBLE CAUSE RECOMMENDED ACTION ,0
11. Toner cartridge is damaged.
Inspect the toner cartridge for a scratched photosensitive drum or toner leaking through worn seals. Replace as necessary. or Inspect the Fusing Assembly for toner build-up or scratches on the fuser rollers Try cleaning with alcohol. Replace the Fusing AssemblV if damaged. Remove and inspect (see Chapter 6 for removal procedure). Cleansing compressed air. Replace if damaged.
2. Fusing Assembly is contaminated damaged.
3. Static Eliminator Strip teeth are contaminated or defective.

Table 7-23

Horizontal
Black Lines RECOMMENDED ACTION
POSSIBLE CAUSE 1. Toner cartridge not seated properly. 2. Toner cartridge defective, 3. Repetitive defect. If the lines are repeated at a consistent interval down the page, this is a repetitive defect.
Remove the cartridge and reinserl it. Replace the cartridge. Refer to Table 7-24 (next), as well as the Repetitive Image Defect Ruler: (Figure 7-9),
Troubleshooting image Formation Troubleshooting

Table 7-24

Repetitive

Defeck

When troubleshooting repetitive image defects, use the Repetitive Image Defect Ruler, supplied in Figure 7-9 to measure the distance between recurring defects. POSSIBLE CAUSE 1. Toner cartridge is damaged. RECOMMENDED ACTION
The circumference of the photoconductive drum inside the toner cartridge is 75 mm (2.95 inches). If the defect repeats at this interval, the defect is associated with the drum. Inspect the drum for scratches or damage, Replace the toner cartridge. Examine and clean rollers in the paper path (refer to Cleaning Printer Components in Chapter 4). The circumference of the lower fusing Pressure Roller is 47 mm (1.85 inches). If the defect repeats at this interval, the defect is associated with the Pressure Roller, Clean the Fusing Assembly using alcohol. If the problem persists, replace the Fusinq Assemblv. Inspect the gears driving the toner cartridge and the Fuser. Replace the Gear Train Assembly if necessary. Try a different paper lot (see Media Specifications in Chapter 2),
2. Dirty Rollers. Any dirty roller in the paper path may result in a repetitive print defect. 3. Fusing Assembly is dirty or defective.
4. Gears are worn, causing slippage or umping. 5. Paper does not meet specs. The surace of the paper maybe too coarse, ~ausing repeated marks.

Table 7-25

Staining POSSIBLE CAUSE RECOMMENDED ACTION

Cleaning (Physical and Electrostatic).

(Primary Charge Roller).

. Writing (Laser Modulation).

Development

(Formation

of the Toner Image).

. Transfer (Charge to transfer the image to paper). The purpose of the Half Self Test Check is to determine which process is malfunctioning. Perform the test as follows: 1. Initiate a printer front panel self test.
Open the printers Top Door after the paper advances half-way through the printer (about ten seconds after the Main Motor begins rotation). The leading edge of the paper should have advanced past the toner cartridge.
3. Remove the toner cartridge. 4.
Open the toner cartridges surface.
drum shield to view the drums
If a dark and distinct toner image is present on the drums surface, assume that the first three functions of the electrophotographic process are functioning (conditioning, writing and developing - see 5), and troubleshoot the failure as a transfer problem. chapter If NO image is present on the photoconductive checks shown on the following pages. drum, perform the
Troubleshooting Drum Rotation Functional Check
Drum Rotation Functional Check
The photoconductive drum, located in the toner cartridge, must rotate for the mint mocess to work. The ~hotoconductive drum receives its d&e fr;m the Main Motor g&r train. To verify whether the drum is rotating 1. Open the printers Top Door. Remove the toner cartridge. 3. Mark the cartridges drive gear with a felt-tipped the position of the mark. 4. marker. Note
Install the toner cartridge, and close the Top Door. The start-up sequence should rotate the drum enough to move the mark. Open the printer, and inspect the gear that was marked in step 3. Verify that the mark moved.
If the mark did not move, inspect the gear train to ensure that it is meshing with the toner cartridge gears. If the printers drive gears appear functional, and the drum does not move, replace the toner cartridge. This test is especially important cartridges have been used. if refilled toner
Troubleshooting High-Voltage Power Supply Check
High-Voltage Power Supply Check
The High-Voltage Power Supply circuitry, on the DC Controller PCA, provides the necessary voltages for the printers electrophotographic processes. A method for verifjring the high-voltage system is given in the table below. Table 7-34

l-ligh-Voltage System Checks
CHECKS 1, Toner cartridge connection points.
ACTION Visually inspect the three connection points on the underside, right end of the toner cartridge. If they are dirty or corroded, clean the connections. Clean using alcohol only. If damaged, replace the toner
2. High Voltage Connector Assembly,
The High Voltage Connector Assembly mounts on the DC Controller PCA and uses spring-loaded pins to contact the toner cartridge (see Figure 7-2 for locations). Verify that the pins are not dirty or corroded, and that the spring-loading action is functional. If the pins are dirty, clean using alcohol only; if damaged, replace the High Voltage Connector Assembly (see lC~apter 6 ~or procedure). -

Paper Curl

Paper curl is inherent to the laser printing processes, and occurs when paper is subjected to heat. Paper curl tends to relax as the paper cools while resting on a flat surface. The specification for maximum paper curl when the paper is lying flat before print is 5 mm (0.2 inches). Although paper curl cannot be totally eliminated, some steps can be taken to lessen its impact, as suggested in the following table. Table 7-35 Causes of Paper Curl RECOMMENDED ACTION
POSSIBLE CAUSE 1. Paper Path

2. Paper Surface

Try using the face-up paper delivery slot to shorten and simplify the paper path. The recommended printing surface of the page is usually marked on the end of a ream of paper, indicated by a small arrow and the phrase print this side first Load paper in the Paper Cassette with the recommended printing surface facing down Jfacing up in the manual feed slot). Over time, paper assumes the characteristics of its storage environment (in a humid environment, paper absorbs moisture; in a dry environment, paper loses moisture). Paper with higher moisture content will tend to curl more. Evaluate the storage conditions of the paper. Ail paper is manufactured differently (different textures, moisture content, drying processes, composition, etc.). Change the type of paper being used and re-evaluate the paper curl results.
3. Paper Storing and Handling

4. Paper Type

Troubleshooting Adjustment Procedures

Adjustment Procedures

Leading Edge Adjustment
The distance from the leading edge of a sheet of paper to the beginning of the printable area can be adjusted using VR301 located on the DC Controller PCA. Leading edge is set at the factory for new units and only needs adjustment when the DC Controller is replaced. VR301 can be accessed without removing any printer assemblies (other than the paper cassette). 1. Run a printer engine test (see Engine Test earlier in this chapter). Measure the leading edge distance (see Figure 7-7). If the distance is 1.5 to 2.5 mm, no adjustment is necessary. 2. If adjustment is needed, remove the paper cassette from the printer by sliding it all the way out. 3. Locate the access hole for VR301 (see Figure 7-7). 4. Turn VR301 clockwise to decrease the leading edge distance, or counter-clockwise to increase (see Figure 7-7). 5. Replace the paper cassette and run another test to compare. 6. Repeat 1 through 5 until the leading edge is within tolerance.

Parts Index Alphabetical Parts Index

Alphabetical Parts Index

DESCRIPTION Arm, Input Paper Sensor Beam-to-Drum Beam-to-Drum Mirror Assembly, LJ 4U4ML Mirror Assembly, LJ 4P/4MP I PART NUMBER RF5-0601 -OOOCN RG5-0667-OOOCN RG5-0802-OOOCN RF5-0682-OOOCN RB1-3073-OOOCN RB1 -2971 -OOOCN RBI -3132-OOOCN RB1 -3356-OOOCN RBI -3681 -OOOCN RBI -3143-OOOCN RBI -3143-OOOCN RG5-0812-OOOCN RG5-0816-OOOCN RG5-081 O-OOOCN RG5-0685-OOOCN RB1-3352-OOOCN RF5-0597-OOOCN RF5-0681-OOOCN RB1 -3130-OOOCN RBI -3130-OOOCN RG5-0700-OOOCN 1252-5278 1252-5460 C2003-69003 RG5-0753-OOOCN C2005-69003 RG5-0822-OOOCN
8-6 8-5 8-5 8-3 8-5 8-6 8-2 8-3 8-6 8-10 8-9 8-3 8-3 8-3 8-2 8-3 8-2 8-3 8-2 8-3 8-7 8-4 8-4 8-7 8-7 8-7 i 8-7
Bezel Assembly, LJ 4P/4MP Bushing Bushing, D-roller Button, Lock, LJ 4U4ML Button, Lock, LJ 4P/4MP Cap, Laser Shutter Claw, Separation Claw, Separation Control Panel Assembly, LJ 4P/4MP Control Panel PCA, LJ 4P/4MP Cover Assembly, LJ 4P/4MP Cover Assembly, LJ 4U4ML Cover, Font, LJ 4P/4MP Cover, Main, LJ 4U4ML Cover, Main, LJ 4P/4MP CRG Pressure Piece, LJ 4U4ML CRG Pressure Piece, LJ 4P/4MP DC Controller Case Assembly DC Controller Connector, LJ 4U4ML DC Controller Connector, LJ 4P/4MP DC Controller PCA, 100-1 20V, LJ 4U4ML (Exchange) DC Controller PCA, 100-1 20V, LJ 4U4ML (New) DC Controller PCA, 100-120V, LJ 4P/4MP (Exchange) DC Controller PCA, 100-120V, LJ 4P/4MP (New)

Parts Index-2

DESCRIPTION DC Controller PCA, 220-240V, LJ 4L/4ML (Exchange) DC Controller PCA, 220-240V, LJ 4L/4ML (New) DC Controller PCA, 220-240V, LJ 4P/4MP (Exchange) DC Controller PCA, 220-240V, LJ 4P/4MP (New) Display Cable, LJ 4P/4MP Door, Back Assembly, LJ 4L/4ML Door, Back Assembly, LJ 4P/4MP Door, I/O, LJ 4L/4ML Door, Memory, LJ 4U4ML Door, Power, LJ 4U4ML Door, Top, LJ 4L/4ML Door, Top, LJ 4P/4MP Drive Gear, LJ 4P/4MP Dust Cover, Foam Rubber E-Clip, LJ 4L/4ML E-Clip, LJ 4P/4MP Fan Assembly Flaq, Exit Sensor Font Door Plug, LJ 4MP only Font Guidej LJ 4P/4MP Foot, Chassis Formatter PCA, LJ 4L (Exchange) Formatter PCA, LJ 4L (New) Formatter PCA, LJ 4ML (Exchange) Formatter PCA, LJ 4ML (New) Formatter PCA, LJ 4MP (Exchange) Formatter PCA, LJ 4MP (New) Formatter PCA, LJ 4P (Exchange) Formatter PCA, LJ 4P (New)
PART NUMBER C2003-69004 RG5-0767-OOOCN C2005-69004 RG5-0823-OOOCN RG5-0815-OOOCN RG5-0691 -OOOCN RG5-0691 -OOOCN RB1 -2977-OOOCN RBI -2979-OOOCN RBI -2978-OOOCN RB1 -3129-OOOCN RBI -3332-OOOCN RS5-0364-OOOCN RB1 -3392-OOOCN XD2-1 100-242CN XD2-I 100-242CN RG5-0703-OOOCN RBI-3097-OOOCN C2040-40002 C2005-00004 RB1 -3001 -OOOCN C2004-69001 C2004-67901 C2016-69001 C2016-67901 C2041-69001 C2041 -67901 C2006-69001 C2006-67901
I FIG I 8-7 8-7 8-7 8-7 8-3 8-2 8-3 8-2 8-2 8-2 8-2 8-3 8-6 8-6 8-2 8-3 8-4 8-12 8-3 8-4 8-6 I 8-4 8-4 8-4 8-4 8-4 8-4 8-4 8-4

Parts Index-3

DESCRIPTION Front Oblique Roller Assembly Front Panel Button, LJ 4U4ML Fuse FUIO1, 100-120V Fuse FUI 01, 220-240V Fuse FU201, 100-120V ONLY Fuser Assembly, 100-120V (Exchange) Fuser Assembly, 100-120V (New) Fuser Assembly, 220-240V (Exchange) Fuser Assembly, 220-240V (New) Fuser Delivery Assembly Fuser Film Assy, 100/1 20V Fuser Film Assy, 220/240V Gear Train Plate Assembly, LJ 4U4ML Gear Train Plate Assembly, LJ 4P/4MP Grounding Plate, LJ 4P/4MP Grounding Plate, LJ 4P/4MP Guide, Feeder Assembly, LJ 4L/4ML Guide, Feeder Assembly, LJ 4P/4MP Guide, Forms Size Guide, Fuser Entrance Guide, Lock Button, LJ 4L/4ML Guide, Lock Button, LJ 4P/4MP High Voltage Connector Assembly Hinge, Font Cover, LJ 4P/4MP 1/0 Cover Plate, LJ 4MP only 1/0 Cover Plate, LJ 4P Keyboard Overlay, Chinese Keyboard Overlay, Danish

Index-3

Oblique Roller Assembly, Front 6-20 operating environment 2-2 operating requirements 2-1-2-16 optional printer memory 3-10 ordering consumables 1-17, 8-3 parts 1-17, 8-2 related documentation 1-18 overcurrent protection (theory) 5-10 overhead transparency specs 2-15 ozone emission 1-14
Control Panel (LJet 4P/4MP) 6-13 DC Controller 6-43 Formatter 6-15 PCE 1-17,8-2 performance specifications 1-4 phone numbers CIC (Customer Info Center) 1-21 consumables 8-3 CSC (Customer Support Ctr) 1-21 DMO 8-3 PCE 8-2 PDO 8-2 P printer drivers 3-7 Pacing, serial I/O (theory) 5-15 technical assistance 1-20-1-22 page count (LaserJet 4P/4MP) 3-17 photosensitive drum (theory) 5-23 page coverage, 5% 4-4 photosensors (theory) 5-35 page protect 3-10 Pickup Assembly 6-47 page protect (theory) 5-20 Pickup Feed D-Roller 6-46 paper and envelope sizes 2-9 pickup jams (theory) 5-39 paper capacities 1-2 Pickup Solenoid 6-41 Paper Cassette Assembly 3-4,6-21 pin configuration paper cassette empty parallel B-2 control panel message 3-10 serial B-3 paper cassette loading 3-4 PJL Overview (theory) 5-21 paper cassette, printing (theory) 5-37 Plunger Assembly, Top Door Switch 6-53 paper curl 7-42 power cord 3-5 paper feed area, paper jams 4-9 Power Door 6-6 paper feed system (theory) 5-33-5-39 Power Switch 6-25 Paper Guide/Top Oblique Roller 6-26 power system (theory) 5-3-5-11 paper handling 3-21 power-on jams (theory) 5-39 paper jam detection (theory) 5-39 print capacity, toner 4-4 paper jams print density adjustment (theory) 5-17 clearing 4-8-4-12 print engine control (theory) 5-5 continuous, due to PS l/PS2 6-40 print media specflcations control panel message 3-10 envelopes 2-12 paper light 3-10 print quality adjustment 3-21 ~a~er motion. monitoring and control. m-int skew adjustment 7-44 (theory) 5-5 ~rint speed 1-2 paper movement, overview (theory) 5-34 print utilities l-lg paper out sensor, PS2 (theory) 5-35 printer serial number 1-3 paper output area, paper jams 4-12 Printer Covers paper path and components 7-4 LaserJet 4L/4ML 6-7 paper sensors (theory) 5-35-5-36 LaserJet 4P/4MP 6-9 paper specifications 2-10 printer dimensions 1-4 parallel cable, bi-tronics B-2 printer drivers 3-7 parallel interface (theory) 5-14 printer drivers, obtaining 3-7 parts, ordering 1-17,8-2 7-6-7-18 printer error troubleshooting Parts Center Europe (PCE) 1-17,8-2 printer features list 3-21 Parts Direct Ordering (PDO) 1-17,8-2 printer languages 1-2 parts index printer lights, fimctions 3-10 listing by name A-2 - A-8 printer space requirements 2-3 listing by part number A-9 - A-16 printing a self test 3-19-3-24 printing engine test - LJet 41J4ML 7-36

Index-4

7-37 removal and re~lacement 6-1 Beam to D-rum Mirror 6-29 Control Panel (LJet 4P/4MP) 6-13 cover and doors 6-6-6-14 DC Controller Assembly 6-39 DC Controller Fuses 6-42 DC Controller PCA 6-43 DC ContJScamer Connector 6-53 Fan 6-24 R Feeder Guide Assembly 6-49 radio frequency interference (RFI) 1-15 Formatter PCA 6-15 RAM7ROM error (53 ERROR) 7-14 Formatter Shield 6-15 RAM size 3-21 Front Oblique Roller 6-20 random access memory (RAM) (theory) Fusing Assembly 6-30 5-13 Gear Train Assembly 6-17 read only memory (ROM) (theory) 5-13 High Voltage Connector 6-42 Ready light 3-10 I/O Door 6-6 rear assemblies 6-30-6-38 Input Paper Sensor Arm 6-56 Rear Door 6-12 Laser/Scanner Assembly 6-23 receiving data Lower Output Roller 6-38 control panel message 3-10 Main Motor 6-19 recoverable errors 7-7 Memory Door 6-6 recycling toner cartridges 2-7 memory upgrade 6-4 refilled toner cartridges 2-7 Paper Cassette Assembly 6-21 related documentation 1-18 Paper GuiddTop Oblique Roller 6-26 remanufactured assemblies 1-17 Pickup Assembly 6-47 removal and replacement strategy 6-2 pickup Feed D-Roller 6-46 Pickup Solenoid 6-41 Power Door 6-6 Power Switch 6-25 Printer Cover (LJet 4L/4ML) 6-7 Printer Cover (LJet 4P/4MP) 6-9 Rear Door 6-12 Small Media Roller 6-50 Static Eliminator Strip 6-51 Toner Cartridge Lever 6-52 Top Cover Switch (Plunger) 6-53 Transfer Roller and Guide 6-27 Transfer Roller Buehings 6-28 Upper Output Roller 6-37 repair philosophy 1-17-1-19 repetitive image defect ruler 7-46 re~uired tools 6-3 requirements operating 2-1 2-16 site 2-2 -2-3 space 2-3 reset cold 3-28 menu of 3-27 NVRAM 3-29 simrde 3-26 resetting the printer 3-26-3-30
minting emzine test - LJet 4P/4MP priorit~of elrors 7-7 processing data control panel message 3-10 product information 1-1-1-22 product overview 1-6-1-10 PS1 (theory) 5-36 PS2 (theory) 5-35

Index-5

Resolution Enhancement technology (REt) (theory) 5-17 resolution, print 1-2 RFI statement 1-15 roller, Small Media 6-50
safety information 1-11-1-14 safety, toner 1-14 caving toner (EconoMode) 4-5 scalable typeface list 3-21 ScanJet compatibility 1-2 scanner error (52 ERROR) 7-13 screws, length (DC Controller) 6-40 screws, used in printer 8-4 self test continuous 3-24 engine 3-25 printing 3-19-3-24 printout, LaserJet 4L 3-21 printout, LaserJet 4P/4MP 3-23 sequence of operation (theory) 5-40 Serial I/O (theory) 5-15 serial number 1-3 service approach 1-17-1-19 service checkpoints 4-2 service errors 7-11 service mode 3-15-3-18 shipping damage 3-3 shipping print media 2-16 SIMMS, memoryflanguage 6-5 simple reset 3-26 site requirements 2-2 -2-3 skew adjustment 7-44 skip demo, service menu item 3-18 SL2, Pickup Solenoid 6-41 Small Media Roller assembly 6-50 small media rollers (theory) 5-38 software package, printing 3-8 solenoid, Pickup (SL2) 6-41 solenoids (theory) 5-35 specifications printer 1-4- 1-5 printer dimensions 1-4 adhesive labels 2-13 electrical 1-4 envelope 2-12 media 2-8-2-16 performance 1-4 trans~arencv 2-15 speed, pri;t 1-2Static Eliminator Strip Assembly 6-51 status lights, fimctions 3-10 storage conditions, toner cartridge 2-4

Troubleshooting Engine Test

Engine Test

The engine test print is used to verify that the print engine is functioning correctly. The Formatter PCA is completely bypassed during an engine test. This testis therefore very useful for isolating printer problems. The engine test prints a full page of vertical lines down the entire printable area, and is thus also useful for checking and adjusting registration.
Engine Test Button Location
The engine test print button(SW301) is located on the side of the DC Controller PCA (see Figure 7-2). It is accessible through a hole in the Gear Train plate.
Printing an Engine Test - LaserJet 4L/4ML
On the LaserJet 4L/4ML, the engine test button is accessible without removing the covers, through the I/O Door area on the left side of the printer. To print an engine test, use a long object (such as a pencil) to press the engine test button (see Figure 7-4). (Do not use a metal object.) A single test page is printed.

gure 7-4

Engine Test Button and Printout, LaserJet 4L/4ML
Printing an Engine Test - LaserJet 4P/4MP
On the LaserJet 4P/4MP, the printers covers and the Formatter PCA must be removed prior to printing an Engine Test. Since the covers will be removed, the printers safety interlocks must be defeated to provide power for running the Engine Test. To defeat the interlocks and set-up the printer for an Engine Test: Shield and the
1, Remove the printer cover, the Formatter Formatter PCA (see Chapter 6).
2. Install the paper cassette (with paper loaded). 3. Install a toner cartridge in the ptinter. Lay a large sheet of thick paper over the toner cartridge and Laser/Scanner Assembly to block out ambient room light (this will prevent black streaks on the printed output). 4. On the to~ of the winter, Top DoorPlunge;(sho~ use a ~iece of tape to hold down the in Fi&e 7-5). -

/~{l$$;~;%l%wn

even with chassis TOEIRail to defeat.)

A$~inbly

Figure7-5
Defealing Top Ek90r h,mgw (Law!kfi the P

4P/4MP)

5. On the rear of the Fusing Assembly, use a pencil or flat-blade screwdriver to press the flag mechanism for the Exit Paper Sensor (PS3) in just until it is about flush with the face of the fuser (see Figure 7-6). Do not push the PS3 flag in more than about 1/8 inch (3 mm). If PS3 is pressed in too far, the printer will register a power-on jam and the Engine Test will not print. If this occurs, decrease the depth of the PS3 flag, power-cycle the printer, then retry the Engine Test.
6. Plug the ac power cord into the printer. 7. Exert downward pressure on the the toner cartridge (through the light-blocking paper) while pressing the Engine Test button SW301. Use a pencil or other non-metallic object to reach through the access hole in the Gear Train plate (similar to that shown in Figure 7-4). 8. If the single page Engine Test does not print, power-off the printer, check the Top Door Plunger to be sure it is held all the way down (step 4), and adjust the depth of the Exit Paper Sensor flag as described in step 5. 7-38