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Text of Printers

IntroductionOne of the most commonly used computer peripherals is the printer. Because there are many types of printers, and because they will comprise a large portion of your troubleshooting efforts, this entire chapter is devoted to them. This chapter discusses various printer types as well as how they work. It also introduces you to common printer problems, troubleshooting techniques, and preventive maintenance procedures that can help you keep the printer working properly. The second most common type of output device used with personal computers is the character printer. These devices are employed to produce hardcopy output of documents and graphics. This chapter introduces the three types of character printers commonly used with personal computers. They include dot matrix, inkjet, and laser printers. The chapter also examines the different types of connection ports and interfaces used with these printers. After completing the chapter, you should be able to identify important features associated with each type of printer. You should also be able to describe the basic operation of all the major printer types. Basic Printer Concepts The best tool you can have to properly care for and troubleshoot printers is a good understanding of how they work and how to properly set them up. If you know the functions of a printers components, you will more easily be able to determine the cause of problems when they occur. A good understanding of configuration and setup procedures will allow you to make the printer accessible to the users who need it.

6.1 Types of PrintersImpact printers place characters on the page by causing a hammer device to strike an inked ribbon. The ribbon, in turn, strikes the printing surface (paper). Several nonimpact methods of printing are used in computer printers. Older, nonimpact printers relied on special heat-sensitive or chemically reactive paper to form characters on the page. Newer methods of nonimpact printing use ink droplets, squirted from a jet nozzle device (ink-jet printers), or a combination of laser/xerographic print technologies (laser printers) to place characters on a page. Currently, the most popular nonimpact printers use ink-jet or laser technologies to deliver ink to the page. Basically, there are two methods of creating characters on a page. One method places a fully shaped and fully filled-in character on the page. This type of character is called a fully formed character. The other method involves placing dots on the page in strategic patterns to fool the eye into seeing a character. This type of character is referred to as a dotmatrix character. Over time, printer technology has improved so that they can produce photo-like images. However, a number of printer technologies are still in use, due to cost and quality differences between them. The three most common printer technologies, dot matrix, inkjet or bubble jet, and laser, are discussed here. Dot-Matrix Printers Dot-matrix characters are not fully formed characters. Instead, dot matrix characters are printed in the form of dot patterns that represent the characters. The readers eye fills in the gaps between the dots. Dot matrix printers are the original type of printer used in PCs; they have been around for a long time. Fortunately, they are no longer used much except for specialized business uses such as printing multiple-page receipts or forms. Dot matrix printers are so

named because they use a matrix of pins to create dots on the paper. Each pin is attached to a solenoid, which, when activated, forces the pin toward the paper. As the print head (which contains the pins) moves across the page, different pins are forced forward to strike a printer ribbon against the paper. Because of this action, dot matrix printers fall into the impact printer category. This process of the print head or pins physically striking the paper often sounds like a horde of mad hornets, and is often very loud. Furthermore, because their printouts are created line by line, dot matrix printers are also considered line printers. The printhead in a dot-matrix printer is a vertical column of print wires controlled by electromagnets. Dots are created on the paper by energizing selected electromagnets, which extend the desired print wires from the printhead. In the printhead, the permanent magnet keeps the wires pulled in until electromagnets are energized, causing them to move forward. The print wires impact an ink ribbon, which strikes the paper. Remember that the entire character is not printed in a single instant of time; it is printed in steps. A typical printhead may contain 9, 18, or 24 print wires. The number of print wires used in the printhead is the major determining factor associated with a printers character quality. A 9-pin printhead generally delivers draft-quality print, whereas 24-pin printheads approach letter-quality print. The components of a typical dot-matrix printer are depicted in Fig 6.1. They consist of a power-supply board, a main control board, a printhead assembly, a ribbon cartridge, a paper-feed motor (along with its mechanical drive gears), and a printhead positioning motor and mechanisms.

Fig 6.1 Parts of a dot-matrix printer.

Dot matrix printers use a continuous form feed to move special paper through the printer. A continuous form feed (also called a tractor feed) comprises two wheels, one on either side of the paper. Each wheel contains spokes, or sprockets, that fit into corresponding holes at each edge of the paper. As the wheels turn, the paper is pulled through the printer. The perforated sides of the paper can be removed once the printout is complete, and the pages can be removed from each other or left attached to each other in a continuous string of pages.

Because of the print process they use, dot matrix printers do not provide very good resolution. That is, text and images usually appear grainy, and if you look closely at a dot matrix printout, you will be able to see each individual printed dot. Furthermore, dot matrix printers are limited in their ability to use color. Most of these printers can use one printer ribbon only (typically black, although another color can be substituted). Although some dot matrix printers can use ribbons with more than one (up to four) colors and or more than one (up to four) printer ribbons, dot matrix printers are not capable of producing as many color combinations as other printer types. One advantage of dot matrix printers is that they are relatively inexpensive. Additionally, because they are impact printers, they can be used for making carbon duplicate or triplicate forms. Because of their simple design, dot matrix printers are also easier to troubleshoot than other printer types. The printers interface may contain circuitry to handle serial data, parallel data, or a combination of the different interface types: Centronics parallel, RS-232 serial, SCSI, USB, or IrDA. At the printer end of a Centronics parallel port, a 36-pin connector. Of course, the computer end of the cable should have a connector that is compatible with the interface being used (for example, a DB-25M connector to plug into the systems DB-25F LPT port). Ink-Jet and Bubble jet Printers Ink-jet printers produce characters by squirting a precisely controlled stream of ink drops onto the paper. The drops must be controlled very precisely in terms of their aerodynamics, size, and shape; otherwise, the drop placement on the page becomes inexact, and the print quality falters. The drops are formed by one of two methods: Thermal shockThis method heats the ink in a capillary tube, just behind the nozzle. The heat increases the pressure of the ink in the tube and causes it to explode through the opening. Mechanical vibrationThis method uses vibrations from a piezoelectric crystal to force ink through a nozzle. Inkjet printers (see Fig 6-2) use ink in cartridges, rather than ribbons, to create text or graphic printouts. The ink cartridge in an inkjet printer contains a small pump, which forces ink out of the reservoir, through a nozzle, and onto the page. Inkjet printers create printouts line by line, so they are considered line printers, but their print mechanisms do not make contact with the page, so they are considered non-impact printers. Inkjet printers provide much better resolution than dot matrix printers and are capable of using colored ink. Unlike dot matrix printers, inkjets can combine basic colors to produce a wide range of colors. Inkjet printers are not nearly as loud as dot matrix printers and are much faster. As you might expect, inkjet and bubble jet printers, because of their ability to print in color inexpensively, are most popular with consumers and end users. Inkjet and bubble jet printers are considered line printers for the purposes of the exam. A variant of the inkjet printer is the bubble jet printer. Bubble jets resemble inkjets, but their ink cartridges contain heating elements rather than pumps. When the element is heated, the ink expands and forms a bubble of ink on the nozzle. When the bubble becomes large enough, it bursts onto the paper and creates a dot of color. Although this process sounds messy, bubble jets provide better printouts than the original inkjets. Today, generally, the term inkjet is used to refer to all printers that use ink, including inkjets, and bubble jets. The ink-jet nozzle is designed to provide the proper shape and trajectory for the ink drops so that they can be directed precisely toward the page. The nozzles are also designed so that the surface tension of the ink keeps it from running out of the nozzle uncontrollably. A special variety of ink-jet printers referred to as solid ink-jet printers (also called wax-jet printers) combines thermal printer technology with ink-jettype operations to produce

brilliantly colored pictures and images. Instead of working with inks, these printers melt dyed wa

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