HP Laserjet 4 Manual
Have a look at the manual HP Laserjet 4 Manual online for free. It’s possible to download the document as PDF or print. UserManuals.tech offer 1114 HP manuals and user’s guides for free. Share the user manual or guide on Facebook, Twitter or Google+.
![](/img/blank.gif)
If a failure occurs during this period, the following errors may be displayed: 50 SERVICEThis error occurs when the fusing roller fails to reach the correct temperature in the required time (see “50 SERVICE”) in Chapter 7). 51 ERRORThis error occurs when the BD signal is not received by the DC controller, (see “51 ERROR BEAM DETECT)” in Chapter 7). 52 ERRORThis error occurs when the scanner motor fails (see “52 ERROR,” Chapter 7). Functional Overview 5-39
![](/img/blank.gif)
Print Period When the leading edge of the paper activates the input/registration sensor (PS1), the DC controller forces the laser diode ON until a BD signal is received. Next, the DC controller receives a VIDEO data stream ( VDO) from the formatter. The DC controller translates the VDO data into a VIDEO OUT signal ( VDOUT), which modulates the laser diode ON and OFF, creating intermittent bursts of laser light which reflect off the scanner mirror and onto the photosensitive drum to form a latent electrostatic image. VDO data is sent from the formatter for each scan line of print data on a page, and a BD signal must precede each VDOUT line data received by the DC controller. When the paper exit sensor (PS3) is activated by the leading edge of the first page, the DC controller allows the Fusing Roller to warmup to 183° C. After the last VDO data is sent for the last line of print data on the first page, the formatter sends a PRNT signal for the second page. About 1.87 seconds after the first VDO signal is sent from the formatter, the High Voltage PCA applies positive high voltage to the transfer roller. When the DC controller identifies the last line of print data on the first page, the laser diode is forced ON and generates a sweep beam used to adjust the laser power. 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 searches for a PRNT signal to begin the second page. When the DC controller receives the next PRNT signal from the formatter, the DC controller anticipates receiving a BD signal and energizes the pickup roller clutch solenoid (PC tray-SL1, MP tray-SL2, or lower cassette SL3) about 1.0 second before it receives the BD signal, and the second page feeds from the paper tray. Until the DC controller receives the expected BD signal, a nominal positive voltage is applied to the transfer roller to prevent toner build-up while the transfer Roller is in direct contact with the drum. 5-40 Functional Overview
![](/img/blank.gif)
The formatter then sends VDO data to the DC controller. The DC controller translates the VDO signal into a VIDEO OUT signal ( VDOUT), which modulates the laser diode ON and OFF, creating intermittent bursts of laser light that are reflected off the scanner mirror and onto the photosensitive drum to form a latent electrostatic image. Upon receipt of a BD signal from the DC controller, VDO data is sent from the formatter for each scan line of print data on a page. Before the next sheet of paper arrives, the voltage on the transfer roller switches from the nominal standby voltage to a positive high voltage, to prepare to transfer the toner image from the drum to the paper. The process repeats for each successive page as necessary. If a failure occurs during this period, the following errors may be displayed: 41 ERRORThis error occurs when a sheet of paper is fed too soon or when an unstable BD or TOP signal is received (see “41.x ERROR” message in Chapter 7). 50 SERVICEThis error occurs when the fusing roller fails to rise to the correct temperature in the required time (see “50 SERVICE”) in Chapter 7). 51 ERRORThis error occurs when the BD signal is not received by the DC controller (see “51 ERROR” in Chapter 7). 52 ERRORThis error occurs when the scanner motor fails (see “52 ERROR” in Chapter 7). Functional Overview 5-41
![](/img/blank.gif)
Last Rotation Period After printing is complete, the Last Rotation period begins, during which residual static charges are eliminated from the photosensitive drum to prepare for the next printed page. About 1.7 seconds after the Last Rotation period begins, a nominal standby voltage is applied to the transfer roller to stop the toner attraction. Then, 4.0 seconds after the Last Rotation period begins, the negative DC high voltage on the primary charging roller is turned OFF, leaving the AC voltage to neutralize the drum’s surface. Finally 5.98 seconds after beginning the Last Rotation period, the transfer roller voltage returns to a negative high voltage, and any toner on the surface of the transfer roller is attracted to the photosensitive drum. At the end of the Last Rotation period, the fusing roller returns to 172° C, the main motor turns OFF, the scanner motor turns OFF, the AC high voltage to the primary charging roller turns OFF, the transfer roller voltage returns to 0 volts, and the printer returns to the Standby period. About 30 seconds after the printer returns to the Standby period, the exhaust fan switches to low-speed rotation. When another PRNT signal is sent from the formatter, printer operation resumes. 5-42 Functional Overview
![](/img/blank.gif)
6 Removal and Replacement This chapter describes the complete disassembly of the printer from the beginning. In every instance, tasks that must be performed before beginning the procedure are listed first. Remove the assemblies in the order listed to prevent damage during re-assembly. Removal and replacement of user-replaceable maintenance items is shown in Chapter 4, “Preventive Maintenance.” These items include: •All Pickup Rollers and Separation Pad •Transfer Roller Replacement •Installing the Toner Cartridge Servicing the printer involves replacing printed circuit and electro-mechanical assemblies. Do not repair component failures within these assemblies. In all instances, replace the failed assembly. The assembly procedure is the reverse of the removal procedure, except where specific instructions are provided. CautionPower-off the printer and disconnect the power cord from the power outlet and the printer before servicing the printer. Some sheet metal edges, particularly around the formatter cage, are sharp. Be careful when working in these areas to avoid being cut. NoteThe printer contains parts that are sensitive to Electrostatic-Static Discharge (ESD). Always observe proper ESD procedures when servicing the printer. This symbol: appears in this chapter when the parts being serviced are especially susceptible to ESD damage. Removal and Replacement 6-1
![](/img/blank.gif)
Required Tools Hardware Review All screws used in the printer are Phillips head, which require a Phillips screwdriver. Figure 6-1 shows the difference between a Phillips and a Pozidriv screwdriver. Note that the Phillips tip has more beveled surfaces. CautionUse of a Pozidriv screwdriver will damage the screw heads. Use Phillips only. QTY TOOL 1 #2 Magnetized Phillips Screwdriver (6-inch shaft) 1 Small Needle Nose Pliers 1 Small Flat-head Screwdriver (6-inch shaft) 1 5mm Nut driver Table 6-1Required Tools Posidriv Phillips Figure 6-1 Comparing Phillips and Pozidrive Screws 6-2 Removal and Replacement
![](/img/blank.gif)
Table 6-2 describes the screws used in the printers, and provides guidelines to help determine where each type of screw is used. The screws can vary in length depending on the thickness of the material being fastened. Typically, plated screws are used in areas visible to the customer, and black screws are used in all other areas of the printer. Always note where each type of screw is located and replace each one into its original location. CautionTo install a self-tapping screw, first turn it counter-clockwise to align it with the existing thread pattern, then carefully turn clockwise to tighten. Do not over-tighten. If a self-tapping screw-hole strips, repair of the screw-hole or replacement of the affected assembly is required. In the removal and replacement procedures that follow, the number inside the parentheses, such as (4), refers to the number of screws you must remove. DRAWING DESCRIPTION PURPOSE Threaded Phillips screw with lock and flat washerUsed to fasten metal or plastic to threaded plastic or metal. Threaded Phillips washer head screwUsed to fasten metal or plastic to metal when high torque is required. Threaded Phillips w/captive star washerUsed to fasten metal to metal when good electrical contact is needed. Self-tapping Phillips screw Used to fasten metal or plastic to plastic mainframes. Table 6-2Printer Hardware Descriptions Removal and Replacement 6-3
![](/img/blank.gif)
Removing the Covers Right Side Cover Removal LJ 4/4 Plus 1Open the Top Cover and release the Right Side Cover by pressing at the points shown in Figure 6-2. 2Fold the cover away from the printer to release the bottom supports and lift the door off of the printer frame. LJ 5 1Open the Top Cover and loosen the retaining screw on the right side cover located at the upper right rear of the printer. 2Slide the right side cover back and fold the cover away from the printer to release the bottom supports. WARNING!Since the handle is part of the right side cover, the retaining screw must be fully tightened or printer damage or personal injury may result. Figure 6-2 Right Side Cover Release Points 6-4 Removal and Replacement
![](/img/blank.gif)
Top Cover Removal 1Open the Top Cover. 2Remove the Right Side Cover. 3Open the Rear Door. 4Remove the (3) screws shown in Figure 6-3, callout 1. 5Release the (2) latch points with a flat screwdriver while lifting the Top Cover (see callout 2.) 6Carefully lift the top cover to access the Control Panel cable. (continued on next page) Figure 6-3 Front Top Cover Screws and Latches Removal and Replacement 6-5
![](/img/blank.gif)
7Disconnect the Control Panel Ribbon Cable and remove the top cover (see Figure 6-4). Figure 6-4 Control Panel Cable 6-6 Removal and Replacement