printers

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Introduction One 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 hard-copy 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 printer’s 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 Printers Impact 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.

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Page 1: Printers

Introduction

One 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 hard-copy 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 printer’s 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 Printers

Impact 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 dot-matrix 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 reader’s 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

Page 2: Printers

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 printer’s 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.

Page 3: Printers

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 printer’s 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 system’s 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 shock—This 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 vibration—This 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-jet–type operations to produce brilliantly colored pictures and images. Instead of working with inks, these printers melt dyed

Page 4: Printers

waxes and then spray them on the page using ink-jet–like dispersal methods. The wax base used for the printing process produces exceptionally bright colors on all types of paper. However, because these printers are slow and relatively expensive, they are typically found only in professional reproduction and advertising settings.

Note: Inkjet and bubble jet printers are usually inexpensive. The significant costs of these printers are the cartridges: it is not unusual for it to cost between 12 and 25 cents per printed page. So, while inkjet and bubble jets may be inexpensive, often they are not a bargain.

Inkjet printers use friction-feed rollers to move the paper through the printer. In friction feed, a stack of pages is kept in a feeder tray. A rubber or plastic roller uses friction to grab the top page and pull it into the printer. Today, generally, the term inkjet is used to refer to all printers that use ink, including inkjets, and bubble jets.

Fig 6.2 Deskjet Printer

Some advantages to this type of feed are that you don’t have to worry about lining up the page perforations or the holes and sprockets, and you don’t have to separate pages from one another when the printout is finished. Unlike tractor-feed printers, friction-feed printers can be used to print on paper that has an irregular shape or size. You can even print on envelopes and cards.

Note: DeskJet is the proprietary name used for printers made by HP. The term DeskJet has become synonymous with inkjet printer technologies.

Laser Printers

The laser printer modulates a highly focused laser beam to produce CRT-like raster-scan images on a rotating drum. This process was developed by Xerox and is referred to as electrophotographic reproduction.

The drum is coated with a photosensitive plastic, which is given a negative electrical charge over its surface. The modulated laser beam creates spots on the rotating drum. The spots written by the laser take on a positive electrical charge. A negatively charged toner

Page 5: Printers

material is attracted to the positively charged, written areas of the drum. The paper is then fed past the rotating drum, and the toner is transferred to the paper. A pair of compression rollers and a high-temperature lamp work together to fuse the toner to the paper. Thus, the image written on the drum by the laser is transferred to the paper.

The laser beam scans the drum so rapidly that it is not practical to do the scanning mechanically. Instead, the beam is bounced off a rotating, polygonal (many-sided) mirror. The faces of the mirror cause the reflected beam to scan across the face of the drum as the mirror revolves. Using the highest dot densities available, these printers produce characters that rival typeset text.

Laser printers are perhaps the most commonly used printers in office environments. They also provide the best quality and have the most complex structure and process. A laser printer is shown in Fig 6.3. Because there are many components in a laser printer, many things can go wrong. This section provides a description of the laser print process. The more familiar you are with it, the easier it will be for you to discover and troubleshoot problems.

Laser Print Process

From manufacturer to manufacturer, and model to model, the exact arrangement and combinations of components may vary in laser printers. However, the order of operations is always the same. Although some laser printers use slightly different processes, the one described here is the generally accepted order of events. Note that these events occur in cycles, so it is not as important to know which step is first or last; rather, it is order of events that is important. For example, some sources list charging as the first step, while others list cleaning as the first step. It doesn’t really matter which occurs first, but for the purposes of this discussion, we’ll consider the charging step first.

Fig 6.3 A Typical Laser Printer

The six stages of operation in a laser printer include

1. Charging In the charging step, the printer’s high-voltage power supply (HVPS) conducts

electricity to the primary corona wire, which in turn passes the voltage on to the printer’s drum. This voltage is around –5000vDC.

Page 6: Printers

Note: Some newer laser printers use charged rollers instead of corona wires to pass voltage to the drum.

2. Writing The photosensitive drum now contains a very high negative charge. In the writing

step, the printer’s laser begins to move along the drum, creating a negative of the image that will eventually appear on the printout. Because the drum is photosensitive, each place that the laser touches loses most of its charge. By the end of the writing step, the image exists at around–100vDC, while the rest of the drum remains charged to –5000vDC.

3. Developing In this stage, the cover on the printer’s toner cartridge is opened. The toner itself

contains small particles that are attracted to the less negatively charged (–100vDC) areas of the drum. By the end of this stage, the drum contains a toner-covered image (in the shape of the final printout), and the remainder of the drum remains at –5000vDC.

4. Transferring At this point, the paper begins to move through the printer, past the drum. The

transfer corona wire is responsible for applying a small positive charge to the paper as it passes through. This positive charge “pulls” the negatively charged toner from the drum onto the paper.

5. Fusing The only thing holding the toner to the paper at this point is electrical charges. The

toner itself contains resin, which melts when heated. As the paper leaves the printer, it passes through a set of fusing rollers, which have been heated by a fusing lamp. The rollers press the toner onto the paper and the heat on the rollers causes the toner to melt, or fuse, to the paper.

6. Cleaning When the printout is complete, the drum move across a rubber cleaning blade to

remove residual toner. The toner is then deposited into a small reservoir or returned to the toner cartridge. Next, one or more erasure lamps expose the drum to high intensity light. The drum is photosensitive and any remaining charge is eliminated by the light. The printer is now ready to create another image.

Note: Make sure that you are familiar with the laser print process. Knowing this process will help you determine which component is at fault when there is a problem.

When character data is received from the host computer, it is converted into a serial bit stream, which is applied to the scanning laser. The photosensitive drum rotates as the pulse-encoded laser beam is scanned across it. The laser creates a copy of the image on the photosensitive drum in the form of a relatively positive-charged drawing.This operation is referred to as registration.

Before the laser writes on the drum, a set of erase lamps shines on the drum to remove any residual traces of the preceding image. This leaves the complete drum with a neutral electrical charge. A high voltage, applied to the primary corona wire, creates a highly charged negative field that conditions the drum to be written on by applying a uniform negative charge (–600V) to it.

As the laser writes on the drum, the drum turns through the toner powder, which is attracted to the charged image on the drum. Toner is a very fine plastic powder, bonded to iron particles that are attracted to the charges written on the drum. The developer roller, in

Page 7: Printers

the toner cartridge, turns as the drum turns and expels a measured amount of toner past a restricting blade. A regulating AC voltage assists the toner in leaving the cartridge but also pulls back some excess toner from the drum. Excess toner is recycled within the toner cartridge so that it can be used again.

Great care should be taken when installing a new drum unit in a laser printer. Exposing the drum to light for more than a few minutes may damage it. The drum should never be touched; this, too, can ruin its surface. Keep the unit away from dust and dirt, as well as away from humidity and high-temperature areas.

The transfer corona wire (also called the transfer roller or secondary corona wire) is responsible for transferring the toner from the drum to the paper. The toner is transferred to the paper because of the highly positive charge the transfer corona wire applies to the paper. The positive charge attracts the negative toner particles away from the drum and onto the page. A special static-eliminator comb acts to prevent the positively charged paper from sticking to the negatively charged drum.

After the image is transferred to the paper, a pair of compression rollers in the fusing unit (fuser) acts to press the toner particles into the paper while melting them to it. The top roller, known as the fusing roller, is heated by a quartz lamp. This roller melts the toner to the paper as it exits the unit; the lower roller, known as the compression roller, applies pressure to the paper. A cleaning pad removes excess particles and applies a silicon lubricant to the roller to prevent toner from sticking to the Teflon-coated fusing roller.

A thermal sensor in the fusing unit monitors the temperature of the unit. This information is applied to the control circuitry so that it can control the fuser temperature between 140°C and 230°C. If the temperature of the fuser is not controlled correctly, it may cause severe damage to the printer and may also present a potential fire hazard.

A typical laser printer has sensors to determine what paper trays are installed, what size paper is in them, and whether the tray is empty. It also uses sensors to track the movement of the paper through each stage of the printer. This way, the controller knows where the page is at all times and can sequence the activities of the solenoids and clutches properly.

Note: Laser printers are usually very inexpensive from a cost per page perspective. The initial investment is usually higher than an inkjet or bubble jet printer, but the cost per page is usually between 2 and 5 cents.

Page 8: Printers

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 reader’s 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 printer’s 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.

Page 9: Printers

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 printer’s 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 system’s DB-25F LPT port).

Page 10: Printers

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 shock—This 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 vibration—This 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-jet–type operations to produce brilliantly colored pictures and images. Instead of working with inks, these printers melt dyed waxes and then spray them on the page using ink-jet–like dispersal methods. The wax base used for the printing process produces exceptionally bright colors on all types of paper. However, because these printers are slow and relatively expensive, they are typically found only in professional reproduction and advertising settings.

Note: Inkjet and bubble jet printers are usually inexpensive. The significant costs of these printers are the cartridges: it is not unusual for it to cost between 12 and 25 cents per printed page. So, while inkjet and bubble jets may be inexpensive, often they are not a bargain.

Inkjet printers use friction-feed rollers to move the paper through the printer. In friction feed, a stack of pages is kept in a feeder tray. A rubber or plastic roller uses friction to grab the top page and pull it into the printer. Today, generally, the term inkjet is used to refer to all printers that use ink, including inkjets, and bubble jets.

Page 11: Printers

Fig 6.2 Deskjet Printer

Some advantages to this type of feed are that you don’t have to worry about lining up the page perforations or the holes and sprockets, and you don’t have to separate pages from one another when the printout is finished. Unlike tractor-feed printers, friction-feed printers can be used to print on paper that has an irregular shape or size. You can even print on envelopes and cards.

Note: DeskJet is the proprietary name used for printers made by HP. The term DeskJet has become synonymous with inkjet printer technologies.

Page 12: Printers

Laser Printers

The laser printer modulates a highly focused laser beam to produce CRT-like raster-scan images on a rotating drum. This process was developed by Xerox and is referred to as electrophotographic reproduction.

The drum is coated with a photosensitive plastic, which is given a negative electrical charge over its surface. The modulated laser beam creates spots on the rotating drum. The spots written by the laser take on a positive electrical charge. A negatively charged toner material is attracted to the positively charged, written areas of the drum. The paper is then fed past the rotating drum, and the toner is transferred to the paper. A pair of compression rollers and a high-temperature lamp work together to fuse the toner to the paper. Thus, the image written on the drum by the laser is transferred to the paper.

The laser beam scans the drum so rapidly that it is not practical to do the scanning mechanically. Instead, the beam is bounced off a rotating, polygonal (many-sided) mirror. The faces of the mirror cause the reflected beam to scan across the face of the drum as the mirror revolves. Using the highest dot densities available, these printers produce characters that rival typeset text.

Laser printers are perhaps the most commonly used printers in office environments. They also provide the best quality and have the most complex structure and process. A laser printer is shown in Fig 6.3. Because there are many components in a laser printer, many things can go wrong. This section provides a description of the laser print process. The more familiar you are with it, the easier it will be for you to discover and troubleshoot problems.

Laser Print Process

From manufacturer to manufacturer, and model to model, the exact arrangement and combinations of components may vary in laser printers. However, the order of operations is always the same. Although some laser printers use slightly different processes, the one described here is the generally accepted order of events. Note that these events occur in cycles, so it is not as important to know which step is first or last; rather, it is order of events that is important. For example, some sources list charging as the first step, while others list cleaning as the first step. It doesn’t really matter which occurs first, but for the purposes of this discussion, we’ll consider the charging step first.

Fig 6.3 A Typical Laser Printer

Page 13: Printers

The six stages of operation in a laser printer include

1. Charging In the charging step, the printer’s high-voltage power supply (HVPS) conducts

electricity to the primary corona wire, which in turn passes the voltage on to the printer’s drum. This voltage is around –5000vDC.

Note: Some newer laser printers use charged rollers instead of corona wires to pass voltage to the drum.

2. Writing The photosensitive drum now contains a very high negative charge. In the writing

step, the printer’s laser begins to move along the drum, creating a negative of the image that will eventually appear on the printout. Because the drum is photosensitive, each place that the laser touches loses most of its charge. By the end of the writing step, the image exists at around–100vDC, while the rest of the drum remains charged to –5000vDC.

3. Developing In this stage, the cover on the printer’s toner cartridge is opened. The toner itself

contains small particles that are attracted to the less negatively charged (–100vDC) areas of the drum. By the end of this stage, the drum contains a toner-covered image (in the shape of the final printout), and the remainder of the drum remains at –5000vDC.

4. Transferring At this point, the paper begins to move through the printer, past the drum. The

transfer corona wire is responsible for applying a small positive charge to the paper as it passes through. This positive charge “pulls” the negatively charged toner from the drum onto the paper.

5. Fusing The only thing holding the toner to the paper at this point is electrical charges. The

toner itself contains resin, which melts when heated. As the paper leaves the printer, it passes through a set of fusing rollers, which have been heated by a fusing lamp. The rollers press the toner onto the paper and the heat on the rollers causes the toner to melt, or fuse, to the paper.

6. Cleaning When the printout is complete, the drum move across a rubber cleaning blade to

remove residual toner. The toner is then deposited into a small reservoir or returned to the toner cartridge. Next, one or more erasure lamps expose the drum to high intensity light. The drum is photosensitive and any remaining charge is eliminated by the light. The printer is now ready to create another image.

Note: Make sure that you are familiar with the laser print process. Knowing this process will help you determine which component is at fault when there is a problem.

When character data is received from the host computer, it is converted into a serial bit stream, which is applied to the scanning laser. The photosensitive drum rotates as the pulse-encoded laser beam is scanned across it. The laser creates a copy of the image on the photosensitive drum in the form of a relatively positive-charged drawing.This operation is referred to as registration.

Page 14: Printers

Before the laser writes on the drum, a set of erase lamps shines on the drum to remove any residual traces of the preceding image. This leaves the complete drum with a neutral electrical charge. A high voltage, applied to the primary corona wire, creates a highly charged negative field that conditions the drum to be written on by applying a uniform negative charge (–600V) to it.

As the laser writes on the drum, the drum turns through the toner powder, which is attracted to the charged image on the drum. Toner is a very fine plastic powder, bonded to iron particles that are attracted to the charges written on the drum. The developer roller, in the toner cartridge, turns as the drum turns and expels a measured amount of toner past a restricting blade. A regulating AC voltage assists the toner in leaving the cartridge but also pulls back some excess toner from the drum. Excess toner is recycled within the toner cartridge so that it can be used again.

Great care should be taken when installing a new drum unit in a laser printer. Exposing the drum to light for more than a few minutes may damage it. The drum should never be touched; this, too, can ruin its surface. Keep the unit away from dust and dirt, as well as away from humidity and high-temperature areas.

The transfer corona wire (also called the transfer roller or secondary corona wire) is responsible for transferring the toner from the drum to the paper. The toner is transferred to the paper because of the highly positive charge the transfer corona wire applies to the paper. The positive charge attracts the negative toner particles away from the drum and onto the page. A special static-eliminator comb acts to prevent the positively charged paper from sticking to the negatively charged drum.

After the image is transferred to the paper, a pair of compression rollers in the fusing unit (fuser) acts to press the toner particles into the paper while melting them to it. The top roller, known as the fusing roller, is heated by a quartz lamp. This roller melts the toner to the paper as it exits the unit; the lower roller, known as the compression roller, applies pressure to the paper. A cleaning pad removes excess particles and applies a silicon lubricant to the roller to prevent toner from sticking to the Teflon-coated fusing roller.

A thermal sensor in the fusing unit monitors the temperature of the unit. This information is applied to the control circuitry so that it can control the fuser temperature between 140°C and 230°C. If the temperature of the fuser is not controlled correctly, it may cause severe damage to the printer and may also present a potential fire hazard.

A typical laser printer has sensors to determine what paper trays are installed, what size paper is in them, and whether the tray is empty. It also uses sensors to track the movement of the paper through each stage of the printer. This way, the controller knows where the page is at all times and can sequence the activities of the solenoids and clutches properly.

Note: Laser printers are usually very inexpensive from a cost per page perspective. The initial investment is usually higher than an inkjet or bubble jet printer, but the cost per page is usually between 2 and 5 cents.

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6.2 Types of Printer Connections and Configurations

Generally speaking, one of the least difficult I/O devices to add to a microcomputer system is a parallel printer. This is largely due to the fact that, from the beginning of the PC era, a parallel printer has been one of the standard pieces of equipment to add to the system. Serial printers are slightly more difficult to set up because the communication definition must be configured between the computer and printer. The serial port needs to be configured for speed, parity type, character frame, and protocol. However, both of these interface standards are beginning to age and be surpassed by newer interface types.

In particular, printers equipped with a USB interface are easy to configure and offer high-speed transmission of data between the computer and the printer. These printers offer both Plug-and-Play and hot-swapping capabilities, effectively making them a plug-and use tool.

There are a number of different ways to access a printer. For example, you can configure a printer so that it is attached directly to the computer or attached indirectly through a network. You can also configure the printer so that it is accessible to only one person or to an entire network of people. Many printers include multiple interfaces and common printer setups are described in this section.

Printer Cables

One note of caution concerning parallel-printer cables: The IEEE has established specifications for bidirectional parallel-printer cables (IEEE-1284). These cables affect the operation of EPP and ECP parallel devices. Using an older, noncompliant unidirectional cable with a bidirectional parallel device prevents the device from communicating properly with the system and may prevent it from operating. Some failures produce error messages, such as Printer Not ready; others simply leave the data in the computer’s print spooler. The symptom normally associated with this condition is that the parallel device just refuses to operate. If an ECP or EPP device successfully runs a self-test but does not communicate with the host system, check the Advanced BIOS Setup screens to make certain that bidirectional printing has been enabled for the parallel port. If so, check the printer cable by substituting a known IEEE-1284–compliant cable for it.

Parallel Printers

The most common way to attach a printer to a computer is through the computer’s parallel (LPT) port. In fact, most parallel ports can be set to transmission modes designed specifically for use with printers (for instance, ECP mode). To connect a printer in this way, attach the parallel cable to the printer and the computer. The end that attaches to the printer is a 36-pin Centronics connector; the end that attaches to the computer is a DB-25 connector.

It is suggested that you do not use a parallel cable longer than 6 feet, because longer cables are more susceptible to errors caused by EMI. You must also attach the printer’s power cable to a wall outlet or other source of power. If the printer is Plug and Play, the OS will detect it on startup and load a device driver for it. If the printer is not Plug and Play, you will need to manually load a driver for it. To do this, insert the disk that came with the printer and run the Setup or Install program. Because the printer is attached to the parallel port, it will use that port’s IRQ and I/O address assignments.

RS-232 Serial Printers

Cable length should be 10 to 50 feet (15.25 meters). Some references, however, use 100 feet as the acceptable length of an RS-232C serial cable. Serial connections are tricky

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enough without problems generated by the cable being too long. Make the cable as short as possible.

USB Printer

More and more printers are being manufactured to support USB connections. To attach a USB printer shown in Fig 6.4, simply plug it into a USB external or root hub. There is no need to even turn the computer off. If the printer requires an external power supply, plug the printer into a power source. Most USB devices support Plug and Play. If the USB printer does not, load its driver using the Setup or Install program that came with the printer.

Fig 6.4 USB Printer

Network Printers

If a printer is installed in a computer system that is part of a network, any other computer on the network can send work to the printer. Historically, the local computer was attached to the printer through one of the normal printing interfaces (that is, parallel, serial, or USB ports) and also connected to the other remote computers through its network connection. In addition to the signal cable, the local computer’s operating system must be configured to permit the remote stations on the network to print through it to its printer. This relationship is known as print sharing.

Note: Printers are one of the most commonly accessed network resources and are the cause for a majority of network-related trouble calls.

Newer printers, referred to as network-ready printers (such as the HP Jet Direct), come with built-in network interfacing that enables them to be connected directly into the local area network. Most network printers contain an integrated network controller and Ethernet LAN adapter that enable it to work on the LAN without a supporting host computer.

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Other printers may be connected directly to the local area network through a device called a print server port. This device resembles a network hub in appearance and can be used to connect up to three printers directly into the network.

Although some older network printers used coaxial cable connections, newer network printers feature RJ-45 jacks for connection to twisted-pair Ethernet networks. You can relatively easily determine whether a printer is networked by the presence of a coaxial or a twisted-pair network cable connected directly to the printer. The presence of the RJ-45 jacks on the back of the printer also indicates that the printer is network capable, even if it is not being used in that manner.

Note: A network printer is different from a printer that is shared on a network. A true network printer has a NIC and is configured as a separate node on the network. A shared printer is attached to a computer on the network and can be accessed only if that computer is turned on and is attached to the network.

Exercise 6.1 Configuring a Printer as a Shared Resource

1. Determine which computer on the network will act as the print server (the computer that the printer will be attached to).

2. Turn the computer off and attach the printer to it with a printer cable. If the printer is USB it is not necessary to turn the computer off unless directed by the installation procedure.

3. Connect the printer to a power source.4. Turn the computer on and load a device driver for the printer, if required.5. Double-click the My Computer icon.6. Double-click Printers.7. Right-click the printer you want to share, then select Properties.8. Select the Sharing tab (the default setting should be Not Shared).9. Select the Shared option and enter the share name (the name that will identify this

printer to other users).10. Click OK. Other users should now be able to access this printer through the Network

Neighborhood. See Chapter 7 for more information on how to access a shared printer.

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6.3 Care, Service, and Troubleshooting

Printers, as mechanical devices, like all other computer equipment, will eventually fail to operate. When this happens, the problems must be diagnosed and repaired. This chapter presents techniques and tools used to troubleshoot and repair printer problems. It also provides common preventive maintenance procedures for use with the different types of printers.

After completing the chapter, you should be able to identify common symptoms produced by errors in different areas of the various printer types and apply the proper tools and techniques required to correct the indicated problems.

There are a great number of moving parts in printers and, because of the frequency at which they are used, moved, and reloaded with paper, ink, or toner, they are prone to developing problems. The following subsections are designed to introduce you to common problems and their resolutions as well as procedures you can use to care for the computer and prevent the occurrence of problems.

Feed and Output

When the paper does not advance, the output normally appears as one line of dark blocks across the page. Examine the printer’s paper feed selector lever to make sure that it is set properly for the type of paper feed selected (that is, friction feed, pin feed, or tractor feed). If the paper feed is set correctly, the printer is online, and the paper does not move, you need to troubleshoot the paper-feed motor and gear train. Check the motor and gear train by setting the printer to the offline mode and holding down the Form Feed (FF) button. If the feed motor and gear train work from this point, the problem must exist in the control board, the interface cable, the printer’s configuration, or the computer system. If the motor and/or the gear train do not respond, unplug the paper-feed motor cable and check the resistance of the motor windings. If the windings are open, replace the paper-feed motor.

Tractor-feed printers are notorious for feeding paper incorrectly through the printer. The problem is not usually getting the paper through but lining the paper up properly. Recall that these feed mechanisms require special paper, in which each piece of paper is attached to the page before it, much like a roll of paper towels. If the roll of paper is not lined up properly, the text that is supposed to be on one page could split over two pages. When this is the case, continue advancing the roll of paper until it is properly aligned.

Paper Jams

If the paper does not feed at all, the place to begin checking is the paper-tray area. The paper trays have a complex set of sensors and pickup mechanisms that must all be functioning properly to begin the paper handling. Due to the complexity of the paper-pickup operation, jams are most likely to occur in this area.

Check the paper tray to make sure that it has paper in it and that the paper is the correct size. Each tray in a laser printer has a set of tabs that contact sensor switches to tell the control circuitry that the tray is installed and what size paper is in it. A mechanical arm and photo-detector are used to sense the presence of paper in the tray. If these switches are set incorrectly, the printer could print a page that was sized incorrectly for the actual paper size. The various paper tray sensors are illustrated in Fig 6.5.

When paper jams in a printer, the first thing you should do is lift the cover. Look for the paper, and if it is visible, gently try to remove it. Don’t pull too hard because you could end up ripping the page, and the smaller pieces left inside the printer will be even harder to get out. Some printers, typically laser printers, include levers that you can release to more easily remove jammed paper. When removing jammed paper, always pull in the direction

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that the paper normally travels through the printer. Pulling the other way could damage rollers and other internal components.

Fig 6.5 Paper tray sensors.

If the paper feeds into the printer but jams after the process has begun, troubleshoot the particular section of the printer where the jam is occurring—the pickup, registration, and fusing areas; and output devices (collators and duplexers). This information is generally presented to the user through the laser printer’s display panel. Another cause for laser printer jams is the presence of some obstruction in the paper path. Check for pieces of paper that have torn loose and lodged in the printer’s paper path. In most laser printers, mechanical components are part of a replaceable module (that is, the drum, developing, or fusing unit). If the motor and all the exposed gears are working, replace these units one at a time.

Often, a paper jam error indication remains even after the paper has been removed from the laser printer. This problem is typically caused by a safety interlock error. Simply opening the printer’s main access door should clear the error.

Note: The most common procedure you will need to carry out for printers is the replacement of toner or ink cartridges. You should clean the printer each time you replace a cartridge. Always follow the manufacturer’s instructions when cleaning a printer.

If the printer continues to jam often, try using a different paper weight. Printers work best with a particular weight of paper, and if you use paper that is too thin or too thick, jams can occur more frequently. If the paper itself is not the problem, try cleaning the printer of dust and other build-up (techniques are discussed at the end of the chapter). If the printer continues to experience paper jams, you might need to replace the feed rollers.

Print Quality

The Printer Produces Blank Pages

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A blank page indicates that toner has been attracted to the entire page. This condition could be caused by a failure of the primary corona, the laser-scanning module, or the main control board. If the laser is in a continuous “on” condition, the entire drum attracts toner. Likewise, if the primary corona is defective, the uniform negative charge is not developed on the drum to repel toner. Replace the primary corona and/or drum assembly. If the problem continues, replace the laser-scanning module and the main control board. On the other end of the spectrum, a white (or blank) page indicates that no information is being written on the drum. This condition basically involves the laser-scanning module, the control board, and the power supply. Another white-page fault occurs when the corona wire becomes broken, contaminated, or corroded, so that the attracting charge between the drum and paper is severely reduced.

Note: Most laser cartridges use tape on the cartridge to prevent movement and leakage. Make sure all packing tape is removed from a new print cartridge before installing it.

If a dot matrix printer produces blank pages, pay attention to the sound coming from the printer itself. If you cannot hear the pins striking the page, try replacing the print head. If the pins are striking the page but there is a blank printout, there is a ribbon problem. First, check to ensure that the ribbon is lined up with the print head. If the ribbon gets accidentally pulled above or below the print head, no image will be created on the page. If the ribbon is already lined up properly, the ribbon is probably worn out, and you can resolve the problem by replacing the ribbon. The distance between the print head and the paper can be adjusted in most dot matrix printers. This is especially useful for printing multipart forms. Experimenting with the head settings may also reestablish normal printing.

If an inkjet printer produces blank pages, the likely suspect is the ink cartridge. Use the printer’s software utility to determine the amount of ink left in the cartridge. If no such utility came with the printer, remove the cartridge and gently rock it back and forth to determine if there is ink present. If there is not, replace the cartridge. If there is ink, the problem could be a clogged nozzle. Follow the printer manufacturer’s instructions for cleaning the print head/printer cartridge(s) with the provided software. To clean manually, use a clean foam-rubber swab or lint-free cloth slightly dampened with distilled water, again following manufacturer’s instructions.

Random Speckles on the Page

Specks and stains on the page may be caused by a worn cleaning pad or by a defective corona wire. If the cleaning pad is worn, it does not remove excess toner from the page during the fusing process. If the corona wire’s grid does not regulate the charge level on the drum, dark spots appear in the print. To correct these situations, replace the corona assembly by exchanging the toner cartridge or drum unit. Also, replace the cleaning pad in the fusing unit. If the page still contains specks after you change the cartridge, run several pages through the printer to clear excess toner that may have collected in the printer. If any type of printer produces a page with speckles or blotches on it, try cleaning the printer. Ribbon ink, cartridge ink, and toner can be deposited within the printer itself and transferred onto the paper as it passes through the printer. Cleaning procedures are discussed later in the chapter.

Repeated Speckles or Blotches

Faults in the print output that occur at regular intervals along the page are normally caused by mechanical problems. When roller and transport mechanisms begin to wear in the printer, bad registration and bad print appear in cyclic form. This problem can be attributed to the dimensions of cyclic components such as the drum, the developing roller in the toner

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cartridge, or the fusing roller. When you have cyclic problems, examine the various mechanical components for wear or defects.

Repeated speckles are those that appear at regular intervals on each page or down the entire length of a page. Again, for any printer type, try cleaning the printer first, paying particular attention to the feed rollers. If there are repeated speckles in a laser printout, suspect the drum. If there is a small nick in the drum, toner will collect there and be transferred onto each page. In addition, during the cleaning step, some drums lose their ability to drop their charge. In either case, replacing the drum may solve the problem.

Printout Contains a Faint Image of the Last Printout

Faint print in a laser printer can be caused by a number of different things. If the contrast control is set too low, or the toner level in the cartridge is low, empty, or poorly distributed, the print quality can appear washed out. Correcting these symptoms is fairly easy: Adjust the contrast control, remove the toner cartridge, inspect it, shake it gently (if it is a sealed unit), and retry it.

If the print does not improve, replace the toner cartridge. Other causes of faint print include a weakened corona wire or a weakened high-voltage power supply that drives it. Replace the unit that contains the corona wire. Replace the high-voltage power supply. Make sure that latent voltages have been drained off the high-voltage power supply before working with it.

A ghosted image occurs when an image from a previous printout appears on subsequent printouts. This phenomenon occurs only in laser printers and indicates a cleaning process failure. The drum, as explained, might have lost the ability to drop its charge in the presence of light. Replace the drum to try to resolve the problem. If the drum is not the cause, it could be either the cleaning blade or the erasure lamps. The erasure lamps are not usually easy to replace, you will probably have to send the printer back to the manufacturer or to a specialized printer repair shop. Make sure that latent voltages have been drained off the high-voltage power supply before working with it.

The Printout Uses the Wrong Colors

Assuming this is not an application-related setting, a problem with incorrect colors is almost exclusively limited to inkjet printers. If the nozzle on one or more of the colors on a color ink cartridge gets clogged, the colors may come out “dirty” or might not be produced at all. Use isopropyl alcohol on a cotton swab to remove dried ink and unclog the nozzles. Another possible cause of this problem is the level of ink. If one color in the color cartridge gets low, the proper shades will not be produced. To resolve this problem, check the cartridge, cleaning the print head and if that doesn’t work replace the cartridge.

The Printout Is Smudged

If a dot matrix printer produces a smudged printout, check the pins on the print head. Stuck pins can cause printouts to have a smudged appearance as they drag across the page. If this is the case, replace the print head.

Note: If you notice that the printer ribbon is shedding fabric you most likely have a stuck printer pin. This almost always requires print head replacement.

Smudged print is normally a sign of a failure in the fusing section. If the fusing roller’s temperature or pressure is not sufficient to bond the toner to the page, the print smudges when touched. When the heating element or lamp in the fusing area does not receive

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adequate AC power from the power supply, the toner does not adhere to the page as it should (although there is the chance that the toner can simply be bad and not sticking to the page if a refilled cartridge is being used). This condition results in smudged output. Examine the fuser unit, the power supply, and the fusing roller’s heating unit.

If the printer is an inkjet, the smudges are most likely the result of something or someone touching the printout before the ink has had a chance to dry. However, if the problem persists, try cleaning the printer. If this doesn’t resolve the problem, it could indicate worn-out cartridge nozzles. Simply replace the ink cartridge. Smudged laser printouts are usually the result of a failed fusing process. You might need to replace either of the fusing rollers or the halogen lamp.

The Printer Is Producing “Garbage”

Garbage characters in the printout usually indicate a communications problem between the computer and printer. First, make sure to select the right printer in the Print dialog box. If more than one printer driver is installed, it is possible another printer has inadvertently been selected, which will produce garbage. Next, make sure that the cable is firmly and properly attached. Try turning the printer off and then back on. Restarting the computer may also solve the problem. Check the printer ports resources. Make sure that a proper driver has been loaded. If you suspect the driver is corrupt, remove it and reload it. Ensure that the printer port has been assigned the proper IRQ and I/O addresses. If this is a parallel port, you will need to check the resources of the port itself.

Note: Whenever you are faced with an unfamiliar print-quality problem in a laser printer, suspect the drum. If this does not solve the problem, use your knowledge of the laser print process to determine which step (and therefore, which component) has failed.

If there is more than one printer port on the computer (LPT1 & 2 or multiple USB ports), try the printer in another port or with another computer. Look at the printer settings in the OS to ensure that the attached printer matches the type selected in the printer settings area. Finally, this problem could be the result of insufficient printer memory. You can test this hypothesis by trying to print a very small document. If it works, there is a good chance that the original document was too large for the printer’s memory. You can add more RAM to the printer using the same modules that the computer uses (SIMMs or DIMMs). Whenever you are faced with an unfamiliar print-quality problem in a laser printer, suspect the drum. If this does not solve the problem, use your knowledge of the laser print process to determine which step (and therefore, which component) has failed.

Errors

Printers are associated with a great variety of error messages. Furthermore, printers often come with their own configuration and monitoring utilities, each with proprietary error messages. Some of the more common errors are described here. Note that these messages could appear on the computer screen or, the printer’s console. Some of these messages are generated by the OS. Any time you receive a printer error message that you do not understand, check the message or error code number in the manufacturer’s documentation.

Note: If your printer is reporting an error that is not documented by the manufacturer, check the Internet. Most printer manufacturers have websites with frequently asked questions (FAQs), troubleshooting forums, or lists of error codes and their meanings.

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Paper Out

This message indicates that there is no paper in the printer. If the printer uses a tractor feed, you will need to lift the printer lid, feed the first sheet of the new stack through the paper path, and line up the holes with the feed wheels. As this procedure differs among systems, consult the manufacturer’s documentation.

If you are using a tray-style friction-feed printer such as that used by laser printers and some inkjet printers, simply pull out the appropriate paper tray. Insert a stack of paper, then close the tray all the way. The error message should go away on its own. If you do not close the tray all the way, a “Tray open” or “Close tray” message might appear. If the printer uses an upright friction feed, such as those used in some inkjet printers, follow the steps in Exercise 6-2 to add more paper.

Exercise 6.2Adding Paper to an Upright Friction-Feed PrinterEXERCI1. Release the tray lever at the back of the printer (if so equipped). This will cause the paper tray to drop slightly away from the

friction rollers.

2. Place a small stack of paper in the tray, using the paper guides.

3. Engage the tray lever. This will bring the paper closer to the feed rollers.

4. The printer might automatically detect the paper and continue the print job. If not, look for and press the Paper Advance button on the printer. This instructs the printer to detect and try to feed the paper.

The “Paper out” message could appear even if there is paper in the tray. Again, if the paper gets too low to be grabbed by the feed rollers, the printer will behave as though there is no paper there. If this is the case, remove the paper, then reinsert it in the tray or add more paper to the current stack.

I/O Error

This error can take many forms, including “Cannot communicate with printer” or “There was an error writing to LPT#.” This message is typically reported by the OS and indicates that the computer cannot properly communicate with the printer. Start by ensuring that the printer is turned on. If it is not, turn it on, then try to print. You might need to restart the computer to ensure that it redetects the presence of the printer.

Next, make sure that the printer cable is firmly and properly attached to both the printer and the computer and that a proper driver has been loaded. If you suspect that the driver is corrupt, remove it, then reload it. Ensure that the printer port has been assigned the proper IRQ and I/O addresses. If this is a parallel port, you will need to check the resources of the port itself.

Try the printer in another port or with another computer. Furthermore, look at the printer settings in the OS to ensure that the attached printer matches the type selected in the printer settings area.

Incorrect Port Mode

Again, this error message may be worded differently, but it indicates that the parallel port to which the printer is attached is using the wrong mode. This message usually appears

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on the computer rather than on the printer. Enter the computer’s CMOS settings and change the printer to the proper mode (unidirectional, bidirectional, ECP, or EPP). Consult the manufacturer’s documentation for the correct mode (the error message itself might indicate the proper mode).

No Default Printer Selected

This is a Windows-generated error, indicating that no printer has been installed or that Windows has not been informed of a default printer to use. As well as running the printer’s Setup program, some printers require that you set the printer up in the Windows Printers folder. Double-click My Computer, then double-click Printers. Right-click the icon of the printer you want to set as the default, then select Set as Default. If no printers are listed in the Printers folder, double-click Add Printer, then follow theon-screen installation steps.

Alternatively, you can click My Computer, then click Control Panel, and then click Printers and then follow the installation instructions.

Toner Low

The “Low toner” message applies to laser printers only. It appears well before the toner is completely gone, as an early warning. The computer should continue to print normally. You can make the error message go away by removing the toner cartridge and gently and slowly rocking the cartridge back and forth. This will resettle the toner. Note, however, that this is not a solution to the problem. The reason for the error is to warn you to replace the toner cartridge soon. Most laser printers will not work at all if the toner cartridge is empty.

If the printer is an inkjet, an “Ink low” message could appear or an ink level bar be displayed. Replace the cartridge.

Note: When ink cartridges get low, you should replace rather than refill them. When you buy an ink cartridge, it comes with a new pump/heating element and new nozzles. By refilling an old cartridge, you will be reusing old, possibly worn-out components.

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6.4 Safety Precautions

Printers have lots of moving parts, so there are several safety procedures you should follow whenever you work with or around a printer. Don’t let long hair, clothing, jewelry, or other objects near the feed or exit rollers. Furthermore, don’t try to operate a printer with the cover off. The cartridge in an inkjet printer and the print head in a dot matrix printer move back and forth quickly across the page, and it is possible to get your hands or other objects in the way. This can harm you and the printer’s components.

You must be especially careful when working around laser printers because they contain lasers that can cause eye damage. Fortunately, most printers do not work once their covers are raised. A more common printer-related injury is caused by the fusing equipment. The fusing lamp can generate around 200oF! Any time you open the laser printer to replace the drum or cartridge or to clear a paper jam, give the printer ample time to cool down before you touch any of its parts.

Laser printers also use high voltage and low voltage high-current power supplies. Make sure the laser printer is powered off and unplugged.

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6.5 Preventive Maintenance

Because of the frequency with which printers are used, they require constant maintenance. Fortunately, the maintenance procedures are usually easy. The best thing you can do to prolong the life of a printer and prevent problems from occurring is to clean it regularly. In all printers, small particles of paper can get left behind and cause a potentially harmful build-up. This build-up can hold static, which can in turn damage components through ESD or cause pages to stick together. Removing build-up will also keep the paper path clear, thus reducing paper jams and ensuring that the motion of moving parts is not inhibited. You can remove dust and particle build-up using compressed air or a vacuum. As you clean the printer, be on the lookout for small corners of paper that might have been left behind during the print process or when a paper jam was cleared. If the printer is an inkjet, you should look for and remove ink from the inside of the printer. Ink can leak or get smudged off the paper. As the ink dries, it can cause moving components or paper to stick. Laser printers can accumulate toner. Empty the toner reservoir regularly, and remove other excess toner using a paper towel or cotton swab.

You can also help prevent paper jams and component wear and tear using the proper paper for your printer. If you place typewriter paper and printer paper side by side, you will notice weight and thickness differences. Using the wrong paper can lead to paper jams and cause undue wear on the printer’s components.

Note: The most important preventive maintenance procedure for a printer is regular cleaning.