Exploring Modern Business Laser Printers
Laser printers have come a long way in the last few years. Not too long ago, laser printers were expensive commodities restricted to the few serious businesses that could afford them. However, the precision, speed, printing consistency, and image quality offered by laser printers made them extremely attractive peripherals.
As computer designs continued to advance into the 2000s, laser printers also advanced while printer prices plummeted. Today, laser printers are available for under $200 (U.S.) and have become commonplace in homes and small businesses all over the world. This article shows you how modern laser printers work and explains how to maintain them effectively.
The intense competition between printer manufacturers has resulted in a staggering variety of laser printer models--each with different sizes, shapes, and features. In spite of this physical diversity, every laser printer ever made performs the same set of functions to transcribe the output of a computer into some permanent paper form.
The process seems simple enough, right? In reality, however, It requires a complex interaction of electrical, electronic, and mechanical parts all working together to make a practical laser printer.
Stop for a moment and consider some things that a laser printer must be capable of First, the laser printer can do nothing at all without a host computer to provide data and control signals, so a communication link must be established. To operate with any computer system, the laser printer must be compatible with one or more standard communication interfaces that have been developed.
A printer must be able to use a wide variety of paper types and thicknesses, which can include such things as envelopes and labels. It must be capable of printing a vast selection of type styles and sizes, as well as graphics images, then mix those images together onto the same page.
The laser printer must be fast. It must communicate, process, and print information as quickly as possible. Laser printers must also be easy to use. Many features and options are accessible with a few careful strokes of the control panel.
Paper input and output must be convenient. Expendable supplies such as toner should be quick and casy to change. Finally, laser printers must be reliable. They must produce even and consistent print over a long working life-often more than 1,000,000 pages (expendable items must be replaced more frequently)
What is electrophotographic?
You are probably wondering why people use the term electrophotographic printer when talking about laser printers. In truth, electrophotographic (or EP) is a broad term that refers to a printer that functions using the electrophotographic process.
Laser printers are electrophotographic printers that use a laser beam to write image data, but there are also LED light-emitting diode) page printers that use a bar of microscopic LEDS, instead of a laser beam, to write image data.
Both Laser and LED printers are electrophotographic printers (although laser-type printers are more common). You can learn much more about the electrophotographic process and see how laser and LED printers work in this book. In this book, the terms EP printer, laser printer, and LED printer are interchangeable.
Make it a point to know your laser printer specifications and features before you begin any repair. The specifications and features give you a good idea what the printer can do, which might help you to test it more thoroughly during and after your repair.
A listing of specifications is usually contained in an introductory section of the printer service manual or at the end in an appendix. If you do not have a copy of the printer documentation on hand, the manufacturer can often fax a copy of the specifications directly to you. Remember that there is no standard format for listing printer specifications.
The format is up to the preferences of each manufacturer. Regardless of how the specifications are listed, you will most often find the following specifications: power requirements, interface compatibility, print capacity, print characteristics, reliability life information, environmental information, and physical information. Each of these specifications has some importance, so you should be familiar with them in detail.
Printer Power requirements
As with any electrical device, a printer requires power to function. Voltage, frequency, and power consumption are the three typical specifications that you will find here. Domestic U.S. voltage can vary from 105 to 130 Vac (alternating-current volts) at a frequency of 60 Hz (hertz). European voltage can range from 210 to 240 Vac at
Many current laser printers have a power selection switch that toggles the printer between 120 and 240 V operation. Power consumption is rated in watts (W) Depending on the particular model, laser printers can use up to 900 W during printing. However, most models use an automatic power-down mode that shuts down the major power-consuming components after the printer is idle for several minutes
Printer Interface compatibility
A printer is a peripheral device. That is, it serves no purpose at all unless it can communicate (or interface) with a computer. A communication link between the printer and computer can be established in many different ways.
Print capacity is a generic term including several different laser printer specifications that outline what a printer can do. One of the most common print capacity specifications is print speed which is measured in pages per minute (ppm Inexpensive laser printers work at 20 ppm, but 25 to 30 ppm printers are available.
Next, you must be concerned with resolution, which is the number of individual dots that can be placed per linear inch. Typical laser printers offer 1200x 1200dpi (dots per inch) resolution (1200 lines per inch at 1200 dots per linear inch.)
A resolution this high is adequate for most business and personal graphics. The current generation of laser and LED printers is capable of 600 x 600 dpi resolution. You might find a section on paper specifications. Although dot matrix and ink jet printers are very flexible in accepting a wide variety of paper thicknesses and finishes, the paper used in laser printers must fall within certain weights and finishes if he EP process is to work correctly.
In most cases, standard letter-size, copier grade paper(16-24 pound bond) will work. The paper also should have a plain finish. Shiny or gloss-finished papers will cause problems with the EP process. Most laser printers will handle envelopes, transparencies, and labels. Before choosing such materials, be certain that they are labeled as safe or tested with laser printers. Poor-quality materials can jam and damage your printer.
Memory is another important specification for laser printers. Because laser printers assemble images as full pages of individual bits, the more memory that is available, the larger and more complex an image can be printed. Typical laser printers offer 512 K (kilobytes) to I Mb (megabytes), but 2-3 Mb is required for full-page graphic images that might be produced with software such as CorelDraw. Most laser printers offer memory upgrade options.
Print characteristics specify just how printer images will appear, how they will be produced, or how characters from the printer will be interpreted. Fonts, software emulation, and character sets are the three specifications that you should be most familiar with.
A font is a style of type with certain visual characteristics that distinguish it from other type styles. These characteristics might include differences in basic character formation, accents, and decorative additions (that is, Courier versus Helvetica type).
Early laser printers relied on font cartridges that contained ROMS (read-only memories) that held the image data for each font. To change a font, you changed the cartridge.
However, with the rise of Microsoft Windows and improved memory systems, most current laser printers use soft fonts also allow easy enhancements such as underlining, bold, italic, superscript, subscript, and so on All printers use their own built-in software language" that. is in the printer permanent memory.
The language specifies such things as font formation (dot placement) and size, how to recognize and respond to control codes or control panel input, and more, This software language also tells the printer how to operate, communicate, and respond to problems.
Most of these languages were originally developed by leading printer manufacturers such as Hewlett-Packard, IBM, and Epson, Other manufacturers that wish to make their printers functionally compatible must use a software language that emulates one or more of the existing language standards.
For example most laser printers will emulate the operation of a Hewlett-Packard M602, Emulation in this use means that even though a laser printer is physically and electronically different from a HP M602, it will respond as if it were a HP M602, when connected to a host computer.
Another typical printer language is Postscript. Ordinarily when a character code is sent to a printer, it is processed and printed as a fully formed alphanumeric character or other special symbol.
However, because a character code is not large enough to carry every possible type of text or special symbol (for example, foreign-language characters or block graphics), characters are grouped into character sets that the printer can switch between.
Switching a character set is often accomplished through a series of computer codes or control panel commands. A standard character set consists of 96 ASCII (American Standard Code for Information Interchange) characters.
The 96 characters include 26 uppercase letters, 26 lowercase letters, 10 digits, punctuation, symbols, and some control codes. Other character sets can include 96 italic ASCII characters, international characters (German, French, Spanish, etc.), and unique block graphics
Environmental specifications indicate the physical operating ranges of your pinter Storage temperature and operating temperature are the two most Common environmental conditions. A typical laser printer can be stored in temperatures between -10 and 50°C, but can only be used from 10 to 32°C (on average) It is a good idea to let your printer stabilize at the ambient temperature and humidity for several hours before operating it.
Relative humidity can often be allowed to range from 10 to 90% during storage, but must be limited to a range of 40 to 70% during operation. Keep in mind that humidity limits are given as non condensing values. Non Condensing means that you cannot allow water vapor to condense into liquid form. Liquid water in the laser printer would certainly damage its image-formation system.
Your printer might also specify physical shock or vibration limits to indicate the amount of abuse the printer can sustain before damage can occur. Shock or vibration is usually rated in units of g-force. Keep in mind that laser printers are remarkably delicate devices; any substantial shock or vibration might disturb the optics that direct the laser beam. LED printers are a bit more rugged, but also use optics that can be damaged or misaligned by rough handling.
Physical Printer Information
Physical information about a printer includes such routine data as the printer height, width, depth, and weight. In some cases, an operating noise level specification is included to indicate just how loud the printer will be during operation and standby. Noise specifications are usually given in dBA (A-weighted decibels).
Typical Laser Printer Assemblies
No matter how diverse or unique laser printers might appear from one model to another, their differences are primarily cosmetic. It is true that each printer might use different individual components, but every laser printer must perform a very similar set of actions. As a result, most laser printers can be broken down into a series of typical sections, or functional areas as shown in Fig. 1-3. Before you troubleshoot a printer, you must understand the purpose of each area.
The Printer AC power supply
An AC power supply is usually a simple electronic module that provides energy for the fusing assembly heaters and erase lamp assembly. There is typically little that goes wrong with the ac supply unless a serious fault in the fuser or erase assemblies damages the supply.
The Printer DC power supply
The DC power supply is a fairly rugged and reliable device unless a fault in some part.of the printer circuitry damages the supply. Like the AC power supply, the DC power supply is rugged and durable unless in some other fault in another area of the laser printer causes the problem. A cover interlock in the DC supply shuts down printer operation if a protective cover is opened.
Printer High-voltage power supply
The laser printer process relies on high-voltage (1.000V or more) that is used to create and dissipate the powerful static charges that move toner within an laser printer. Even though specialized components are used in high-voltage supplies, high voltages place a great deal of stress on electronic parts, so high-voltage supplies tend to fail more commonly than ordinary AC or DC supply modules.
Printer Fusing assembly
Images are developed on paper using a fine powder called toner. The toner must be fixed to the paper (otherwise, the toner would smudge or simply blow off the page). Heat and pressure are used to fuse toner to the paper. The fusing assembly uses a set of two rollers in compression, where the top roller is heated to melt the toner. A paper exit sensor detects the passage of paper through the printer, and the thermistor sensor is used to regulate temperature in the heated fusing roller.
Erase lamp assembly
The image that appears on a printed page has been transferred there as a latent image written to a special photosensitive drum. Each time the drum rotates, the latent image must be erased before a new image is written. The erase lamps clear the drum thoroughly and allow the photosensitive surface to accept a new image.
Main Printer Motor
Laser printers rely on substantial mechanical activity. Paper must be drawn from a supply tray, fed to the image formation system, fixed, then fed to the output tray. The mechanical force needed to support all of these activities is provided by a single motor and mechanical drive assembly.
Printer Writing mechanism
The data that makes up an image must be transferred (or "written") to the photosensitive drum. This transfer is achieved by directing light across the drum surface. For a laser printer, writing is accomplished by scanning a laser beam across a drum. For an LED printer, the light generated by individual microscopic LEDS (one LED for every dot) transfers image data to the drum. Writing is controlled by the main logic assembly (or ECP).
Printer Scanner-motor assembly
When a laser is used as a writing mechanism, the beam must be scanned back and forth across the drum surface. This scanning process uses a hexagonal mirror that is rotated with a motor. Note that scanners are not needed for LED printers because there is no beam to scan across the drum.
Printer Paper-control assembly
Paper must be grabbed from the paper tray, registered with the latent image, passed through the image formation system, fused, and passed out of the printer. Although the main motor turns constantly, not all portions of the paper handling system can be in motion at all times.
The paper control assembly provides the sensors that detect the presence of paper in the paper tray, the presence of paper in the manual feed slot, and the sensitivity of each toner cartridge for optimum printing. In addition to sensors, the paper-control assembly provides the paper pickup and registration roller clutches that grab and register the page during printing.
Printer Main logic assembly
The main logic assembly (or electronic control package-ECP) is the heart and soul of your laser printer. The main logic assembly has most of the circuitry that operates the printer, including electronics that communicates with the computer and control panel. Main logic is also responsible for checking and responding to input provided by a variety of sensors. Problems that occur in main logic can range from subtle problems to major malfunctions.
Printer Toner cartridge assembly
The Laser cartridge of a printer is a remarkable piece of engineering that combines the toner supply and much of the printer image-formation system into a single, replaceable cartridge. By replacing the laser cartridge, you also replace delicate, wear-prone parts such as the primary corona, cartridge drum, and developer roller. The modularity of the cartridge simplifies the maintenance of your printer and improves its overall reliability.
Printer Control-panel assembly
Users must be able to interface with the printer to select various options operating modes. Not only do current control panels provide multifunction buttons, but most also provide touch screens display for printer status and menu prompts.
Other Helpful HP LaserJet Printer Support Resources
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