Printers, once a high-priced commodity reserved only for businesses and other institutions, have rapidly become indispensable tools in homes and offices around the world (Fig. 5-1). Printers produce business letters or newsletters, address the mail, plot complex drawings, generate long listings of information, print photo-grade pictures, and perform many other boring, redundant - but vitally important - jobs. The sheer variety of printer sizes, shapes, technologies, and features simply stagger the imagination. Yet in spite of this diversity, every printer ever made performs the same function - to translate a computer's output to paper as an intricate series of dots. This chapter is intended to take you inside of contemporary printers using impact, ink jet, and electrostatic printing technologies.

All printers form an image by placing dots onto a page surface, but carriage-type printers use a discrete print head which is carried left-to-right and right-to-left across a page surface. Once the print head completes a pass, the page advances slightly, and the print head completes another pass. This repetitive cycle continues until the document is completed. It is the print head itself which defines the technology being employed. Impact, ink jet, and thermal transfer printing technologies each make use of carriage-type platforms that are very similar to each other - only the head and head driving circuitry are noticeably different. For the purposes of this book, only impact and ink jet printers will be considered. Thermal transfer printers are devoted to small, point-of-sale printers, and are rarely used in current PC full-page printers. Figure 5-2 illustrates a typical carriage-type printer. There are five key sections to the assembly; the enclosure, the printer logic board, the paper transport system, the carriage transport system, and the print head. Each element is examined in detail below.

The carriage-type printer enclosure is essentially a two-piece plastic assembly. The base enclosure (marked 17 in Fig. 5-2) forms the chassis - electronic and mechanical assemblies are fixed to the base enclosure. As a result, the base enclosure tends to be relatively heavy gauge plastic. The upper enclosure (marked 2) fits directly over the base. The two pieces are held together with little more than four screws inserted from the underside (items marked 22). You may notice that the top enclosure has an open face. When the printer is assembled, an open front gives a technician easy access to the print head and carriage area. A face enclosure (marked 6) snaps into place to provide a cosmetic finish. The paper guide (marked 1) acts as a paper separation pawl. Paper entering the printer enters through a space underneath the guide, while paper exiting the printer exits over the guide. Finally, a small smoked plastic shroud (marked 7) fits into the face enclosure and extends out to cover part of the carriage area. This supplemental covering helps to keep dust and debris out of the carriage area.

The logic board is the heart and mind of a carriage-type printer. You may find a large board (or several different boards) in older printers, but current printer designs are able to carry the printer's power supply and logic on a single small printed circuit board. The power supply can easily be included on the logic board since only a few, low-current, DC voltages are needed by the printer. The logic portion communicates with the host computer (via the parallel port) and stores received characters, then translates each character into dot sequences while driving the carriage and paper advance. The board itself (marked 13 in Fig. 5-2) is actually mounted to a metal sub-chassis (marked 15). A power switch (marked 16) fits into the metal structure and plugs into the logic board. The entire sub-assembly then simply snaps into waiting plastic tabs on the base enclosure. A small control panel (marked 4) plugs into the logic board through a thin control panel.

Paper has to be moved through the printer. The paper transport system is the mechanical sub-assembly responsible for handling paper movements. There are two ways to carry paper through a printer; friction feed and traction (or "tractor") feed. The friction feed system is illustrated in Fig. 5-3. A sheet of paper is inserted between the platen and one or two pressure rollers which are then placed in compression. As the platen advances, pressure between the platen and roller will force the paper through. Since this technique relies on friction, coated or low-friction papers may not work properly. Smooth and even paper feed also relies on even compression between the platen and pressure roller(s). If there is any misalignment, paper will tend to pull (or walk) to the left or right. Friction feed systems do not accommodate continuous forms very well.

The tractor-feed system is illustrated in Fig. 5-4. Continuous-form paper is inserted around the platen, and the sprocket holes in either side of the paper are inserted into corresponding points on the printer's sprocket wheels. Since there is no pressure to force paper through, this approach relies on hard contact between the paper holes and sprocket wheels. As the platen advances, the sprocket wheels also advance and pull the paper through evenly. There is no tendency for the paper to walk, so tractor feed is ideal for long documents or large quantities of forms.

The paper transport for Fig. 5-2 is a tractor-feed mechanism which is integrated into the paper/head transport assembly (marked 9 in Fig. 5-2). A platen index motor (marked 11) mounts to the rear right side of the mechanical assembly, and a gear arrangement between the motor and platen provides the drive force. A platen knob (marked 5) passes through a hole in the upper enclosure and fits into the platen. This allows you to rotate the platen by-hand.

The print head has to carried back and forth across the page surface, so the platen/head transport assembly (marked 9) also contains the carriage transport mechanism. A carriage motor (marked 12 in Fig. 5-2) rotates and draws a pulley attached to the print head cradle. For example, when the motor rotates clockwise, the print head slides to the right along a smooth track. When the motor rotates counter-clockwise, the print head slides to the left. The entire platen/head transport assembly seats into the printer's base enclosure where it is bolted into place.

The print head is an electro-mechanical device which actually transcribes dots onto the page surface. As you saw earlier in this chapter, this book is concerned with two carriage-type print heads; impact and ink jet. A basic impact print head is illustrated in Fig. 5-5. Essentially, the impact print head is little more than a collection of independent solenoids. Typical impact heads have 9 or 24 solenoids, and each solenoid can be fired independently. When an electrical pulse is sent to a solenoid, a hard, small print wire shoots out and impresses itself on the page through an inked ribbon. As the pulse passes, the print wire retracts into the solenoid to be fired again. Since a relatively large amount of energy is required to operate solenoids, impact heads generate a large amount of heat. Impact heads will typically have a metal case and heat sink fins to help dissipate the heat. Never touch an impact print head until it has had ample time to cool.

An ink jet print head does not require an inked ribbon. Instead, the head carries its own ink supply in a rubber bladder as shown in Fig. 5-6. Ink flows to the tip if each nozzle where it is retained by capillary action. Each ink tube is fitted with a small piezoelectric crystal. When an electrical pulse is applied to the corresponding crystal, the crystal suddenly contracts - this ejects a droplet of ink from the nozzle. As the pulse passes, the crystal relaxes and creates a vacuum which draws more ink from the bladder. When the bladder is exhausted, the entire print head is easily replaced. The replacement process is often as simple as unsnapping and removing the spent cartridge, then snapping in a fresh one.

The classic problem with carriage-type printers such as the type dissected in Fig. 5-2 is that, while it is capable of single-sheet operation, each sheet has to be inserted and aligned manually before the page can be printed - a frustrating and labor-intensive operation. Since many ink-jet printer designs are well-suited to high-quality graphic output, printer makers such as Hewlett-Packard developed a carriage-type printer expressly designed to handle single sheets automatically. Figure 5-7 illustrates the HP DeskJet assembly. As with ordinary carriage-type printers, the alternate carriage design features five prominent elements; the enclosure, the printer circuits, the paper transport system, the carriage transport system, and the print head.

The DeskJet-type assembly offers some substantial differences over the classic design. The base enclosure (marked 20 in Fig. 5-7) serves as the printer's chassis. The upper enclosure (marked 5) is molded as a single piece which snaps into place over the base enclosure. A stack of single-sheet paper loads into the front deck of the upper enclosure and is held in place with a paper retainer (marked 7). Notice that the upper enclosure is largely open at the top. This provides a technician with easy access to the ink cartridge and carriage assembly. The top enclosure (marked 1) inserts into hinges on the upper enclosure which allows the top enclosure to swing up or down as needed. When the printer is assembled, the paper output tray (marked 13) receives the sheets ejected from the paper transport. The smoked tray cover (marked 12) sits over the paper output tray and completes the cosmetic image.

The printer in Fig. 5-2 showed only a single printed circuit board which carried the power supply, printer logic, communication circuits, and print head driving circuits. Although the printer in Fig. 5-7 is only slightly more complex, it breaks the circuitry into three separate assemblies; the logic board, the power supply, and the driver board. The logic board (marked 19 in Fig. 5-7) handles all communication between the printer and host computer, and translates stored printer characters into control signals the paper/head transport assembly and print head driver board. A power supply (marked 17) sits adjacent to the logic board. Both the power supply and logic board are mounted to a metal sub-chassis (marked 25). A power switch fits into a sub-chassis hole and connects to the power supply. The entire sub-assembly then sits into the base enclosure. It is interesting to note that the sub-chassis is not bolted or snapped into the base enclosure - resulting in easier assembly at the factory. The print head driver board (marked 15) slides into an available slot in the paper/head transport assembly and connects to the print head cradle. An ink jet cartridge (marked 16) snaps into the cradle. The only other electronic element is the control panel (marked 11) which plugs into the logic board and sits in place beneath the top enclosure.

Single sheets of paper are fed into the printer using a technique very similar to that shown in Fig. 5-8. A small stack of paper fits into the printer. When a new sheet is needed, a paper take-up roller (or "pickup roller") turns once. One rotation will grab the next subsequent page and drag it to the feed rollers, which in turn pull the page in an arc past a fixed platen. As the ink jet print head travels back and forth across the page, the feed roller advances the paper. Once the page is finished, it drops into the paper output tray. The paper pickup and advance motor is built into the paper/head transport assembly (marked 14 in Fig. 5-7).

Of course, the print head must be carried back and forth across the page surface - this is the task of the carriage transport. It works just like the carriage transport covered in the last section. A motor drives a pulley attached to the print head cradle. As the motor turns in one direction, the print head carriage moves in one direction along a fixed track. When the carriage motor reverses, the print head carriage reverses its direction. The carriage transport system is incorporated into the paper/head transport assembly (marked 14 in Fig. 5-7).

The print head used in the printer of Fig. 5-7 is an ink jet cartridge (marked 16). Replaceable cartridges use the same operating principles as the ink jet head shown in Fig. 5-6. You can see a close-up of a contemporary print head in Figure 5-9. Replaceable ink jet print heads offer some unique advantages: they are lightweight, capable of achieving high printing resolutions (better than 300 DPI), and they are easily exchanged with fresh cartridges (this minimizes cleaning hassles and speeds service in the field).

All printers form their images as a series of dots which are transferred to a page surface. Where carriage-type printers operate by passing a print head across the paper and form an image one "line" at a time, page-type printers develop the entire page image which is transferred to a page all at once. Page printers are typically based on electro-photographic (EP) technology. As you see in Figure 5-10, the EP system is one of the most complex and intricate printing systems available - it is also capable of unsurpassed printing quality and consistency at resolutions up to 1200 dots per inch (DPI) and higher. To appreciate the differences between carriage and page printing, you should understand the basics of page printer operation.

In a carriage-type printer, a print head produces the image, and it is easy to see the point at which an image appears on the page. On the other hand, an EP printer requires a variety of assemblies needed to produce a permanent image - in fact, most of the printer is used to make the image (referred to as the image formation system or IFS). Electro-photographic printing starts with a stack of paper in a paper tray (marked 8 in Fig. 5-10). When a printing cycle begins, a single sheet of paper is grabbed by a feed roller (marked 10) and separation pad (marked 9), and is passed to a set of registration rollers (marked 11) which hold the paper sheet in place until the image is ready to be transferred.

EP image formation starts and ends with a photosensitive drum (marked 14) which receives electrical charges across its surface that correspond to the individual dots of the image being formed. A rotating EP drum is erased by exposing it to light from an erase lamp (marked 3). As the drum continues to rotate, a primary corona (marked 4) places a uniform charge along the drum's surface. To form the image, the drum must be discharged at the points where dots are to appear. This is accomplished by means of a "writing mechanism". In the case of a "laser printer", a laser beam is produced and scanned across the drum surface using a laser/scanning assembly (marked 6). The beam is reflected off a beam-to-drum mirror (marked 5) and down to the drum surface. As the beam scans, it is turned on and off corresponding to the presence or absence of each dot. One pass is equal to one complete row of pixels across the page. For a printer working at 300 DPI, one pass (or one "scan line") is 1/300th of an inch. As the drum continues to rotate, areas of the drum discharged by the laser light pick up toner which is attracted to the drum.

At this point, the drum has a "developed" image which can now be transferred to paper. The registration rollers which had been holding the paper now start the page moving. A transfer roller (marked 12) grabs the page and passes it over a transfer corona (marked 13). The transfer corona places a high charge on the paper which attracts toner off of the drum and onto the page surface. Excess toner is gently removed from the drum which is cleaned by the erase lamp assembly in preparation for another pass. The drum continues to rotate as the page moves by, and the image is continuously transferred to paper. The charged paper is discharged by a static eliminator comb, and it moves to the fusing assembly. Toner is still in its powder form, so it must be melted and pressed into the paper. The fusing assembly uses a heated upper fusing roller (marked 18) and a lower pressure roller (marked 19) to accomplish fusing. After that, the completed page is passed in an upward clockwise arc where it is ejected into the paper output tray.

As you can see from Fig. 5-10, an EP printer is hardly a trivial assembly. A great deal of mechanical precision is packed into a relatively small package. Fortunately, EP printer design has evolved to a point where almost all of the critical devices are fabricated into sub-assemblies which can easily be replaced on the workbench. Figure 5-11 illustrates a completed view of a Hewlett-Packard LaserJet III showing the location of each housing screw. Unlike carriage-type enclosures which tend to divide into upper and lower halves, page printer enclosures are a combination of several different upper and lower pieces. You will also note the portion of the upper housing that is swung open - this allows easy access for the user in order to clean the paper path and replace expendable elements such as the toner cartridge and EP "engine" assembly.

Once the upper housings and EP cartridge are removed as shown in Fig. 5-12, you can see many of the major assemblies quite clearly. The erase lamp array and beam-to-drum mirror are located in the access cover itself. Looking down into the main body of the printer, you can see the fusing assembly, plastic feed guide, transfer corona, registration rollers, laser/scanning assembly, and power supplies are all easily visible. Upon closer inspection, you will also note many of the gears and mechanical linkages that interconnect all of the printer's major assemblies. The pickup assembly is not visible in Fig. 5-12 since it is being obscured by other assemblies. Removing the lower enclosure exposes the printer's main circuitry.

When the printer is placed upside-down and the bottom enclosures are removed, the printer's main logic and driver circuitry is exposed as shown in Fig. 5-13. Ultimately, EP circuitry performs the same essential jobs as carriage-type circuitry: communication with the host PC, processing host data into dots and storing that information in memory, running the printer's mechanisms to process each page properly, and responding to a variety of sensory feedback to prevent dangerous printer conditions. The DC Controller board performs most of the logic and printer control functions, while the Interface/Formatter board handles communication, control panel operation, and expansion cartridges. It is important to note here that not all EP printers include so much circuitry. Low-end EP printers may use only one board. You may also note that there are several other small printed circuit boards in the printer. Some of these boards are clutch boards that use solenoids to start and stop various printer mechanics such as the pickup and registration roller assemblies. A control panel board is typically located under the upper front enclosure.

A typical EP printer uses three power supplies: an AC supply, an DC supply, and a high-voltage supply. You can see each supply pointed out in Fig. 5-12. The AC power module is little more than a transformer which provides one or more AC levels to drive the fusing heater lamps. The DC power supply assembly is the printer's main supply which powers the logic, sensors, and main DC motor. Since powerful static charge is vital to the EP printer, a high-voltage power supply assembly is used to drive the coronas. Generally speaking, it is advisable to replace failed power supplies outright - especially the high-voltage supply.

With so many mechanical operations needed in an EP printer, it does not take long for key components (such as the EP drum and coronas) to wear out. Even the various gears and linkages are subject to significant wear. The most substantial design evolution for EP printers was incorporating several key components into a single, easily replaceable assembly such as the ones in Fig. 5-14. It is important for you to remember that not all EP cartridges carry the same components - larger, more expensive EP cartridges tend to pack more components. Simple cartridges only carry toner, and leave the EP "engine" as a separate mechanical sub-assembly. More sophisticated EP cartridges include toner, a fresh EP drum, a new primary corona, and perhaps even more.

As you might imagine, the precision components in an EP cartridge are sensitive and delicate. The photosensitive drum and toner supply are particularly sensitive to light and extreme environmental conditions, so it is important to follow several handling and storage guidelines. First, the photosensitive drum is coated with an organic material that is EXTREMELY sensitive to light. Although a metal shroud covers the drum when the cartridge is exposed, light may still penetrate the shroud and cause unwanted exposure (also known as "fogging"). Deactivating the printer for a time will often eliminate mild fogging. Do NOT defeat the shroud in open light unless ABSOLUTELY NECESSARY, and then ONLY for SHORT periods. This will certainly fog the drum. A seriously fogged cartridge may have to be placed in a dark area for several days. Also, NEVER expose the EP drum to direct sunlight - direct sunlight can permanently damage the drum's coating.

Next, avoid extremes of temperature and humidity. Temperatures exceeding 40 deg C can permanently damage an EP cartridge. Extreme humidity is just about as dangerous. Do not allow the cartridge to become exposed to ammonia vapors or other organic solvent vapors - they break down the drum's photosensitive coating VERY quickly. Finally, keep a cartridge secure and level. Never allow it to be dropped or abused in any way.

Finally, as the toner supply diminishes, it may be necessary to redistribute remaining toner so that it reaches the toner roller. Since toner is available along the entire cartridge, it must be redistributed by rocking the cartridge back and forth along its long axis. If you tip a cartridge upright, remaining toner will fall to one end and cause uneven distribution. You should check the notes provides with your toner/engine cartridges for specific redistribution hints and precautions.

The writing mechanism is the device which exposes a latent image onto the charged EP drum. Beams of light that strike the drum cause those points on the drum to discharge. Those discharged points then attract toner to the drum surface - areas of the drum that were not exposed by the writing mechanism remain charged, and will repel toner. Thus, areas with and without toner develop on the drum. There are typically two well-established technologies available for exposing the drum; laser scanning, and LED bars.

Laser scanning is the classical exposure method - thus the term "laser printer". A laser beam is shot into a rotating hexagonal mirror. As the mirror rotates, the angle of the reflected beam is constantly changing. In this way, the beam is swept across the drum continuously (and always in the same direction). By turning the laser on and off in synchronization with each scan, dots can be aligned between scans with extreme precision. Original laser printers used a separate helium-neon gas laser and spinning mirror assembly. Today, a diode laser and small motor/mirror assembly are combined in the same pre-fabricated sub-assembly. Laser scanning can achieve resolutions of 1200DPI and higher. Unfortunately, laser printers tend to be heavy, and sensitive to physical abuse.

LED bars represent an alternative development in EP printing which is smaller, lighter, and generally more rugged than a laser/scanning assembly. Instead of tracing a modulated laser beam, a row of microscopic light-emitting diodes (LEDs) are fabricated into a single line which is positioned in close proximity to the drum. At 300DPI, an LED bar uses 2550 LEDs to cover an 8.5" width of paper. The ultimate resolution of an LED bar is limited only by the number of discrete LEDs which can be fabricated onto a single bar. However, the LED bar is a sub-assembly unto itself - if one LED should fail, the entire print bar would have to be replaced. For the purposes of this book, you will see EP printers using LED print bars referred to as "LED printers".

This chapter has focused largely on SX-type EP architecture used extensively in laser printers such as the Hewlett-Packard LaserJet II and III from 1986 through 1990. Since 1990, however, continuing advances in EP design have simplified the electro-photographic process, while improving reliability. All of the basic principles have remain unchanged, but the process is more refined as illustrated in Fig. 5-15.

Charge rollers - one of the first things you should notice is that the primary and secondary coronas have been eliminated and replaced with charge rollers. Introduced with the Canon LX EP engine in 1990, the charge rollers have replaced corona wires as a means of applying electrical charges to the EP drum and paper. The charge rollers themselves are little more than a specialized formulation of foam rubber which accepts an even charge across its entire surface area - a key attribute for EP printers.

The main advantage to the charge rollers is the lower high-voltage requirement and the elimination of primary grid circuitry. While a primary corona demands about -6000 volts, a primary charging roller requires only about -1000 volts to achieve the same required -600 volt charge on the drum. This behavior also holds true for the transfer roller working at +1000 volts and delivering a charge of +600 volts to the page. A handy side-effect to these lower charging voltages is a significant reduction in the amount of ozone developed in the printer. Lower ozone eases environmental concerns about ozone exposure and long-term health hazards.

Unfortunately, a noted disadvantage to the charge roller scheme is that direct contact is required with the EP drum and page. In theory, this is not a problem. But in practical applications, you can not escape the dust, hair, pollen, and other airborne debris that will invariably find its way into the printer. Debris that collects on charge rollers has a chance of being transferred to the page (or interfering with the charge uniformity along the roller). Accumulations of foreign matter on the primary charge roller also stand a much greater chance of damaging the EP drum’s photosensitive coating. As it turns out, the transfer roller is more likely to attract foreign matter because of its lower physical position in the printer assembly. To help keep the transfer roller clean, its charge is reversed when the printer is idle. Charge reversal tends to repel foreign matter off the roller.

Erase lamps - another thing you will notice about Fig. 5-15 is that the erase lamps are missing. This is not an accident. With the introduction of charge rollers, the need for erase lamps disappeared. EP designers discovered that adding an AC signal to the DC charging voltage on the primary charge roller effectively recharged the drum without any light exposure. Reports from the field indicate that the absence of erase lamps has made no visible difference in image quality.

Doctor blade - a precise leveling blade (called a "doctor blade") in the development unit served to keep toner on the development roller limited to a single layer. As you might expect, any damage or mis-adjustment to the blade will have a pronounced effect on the image. Recent advances in materials has resulted in a rubber blade that actually rests on the development roller’s surface. This streamlines toner charging while still providing even toner distribution on the roller.

New EP coatings - traditionally, the photosensitive coating applied to an EP drum has been notoriously delicate - even the slightest nick or scratch was known to leave its mark permanently in the drum. Over the last few years, EP coatings have improved dramatically in response to changing market forces. One major reason for the improvements coincides with the introduction of charge rollers. Even a foam rubber roller in direct contact with the EP drum demands a more durable photosensitive coating. Another factor fueling the drum improvements is attributed to the growing remanufacturing market for toner cartridges and engines - drums are being expected to serve much longer lives as they are tested and recycled into remanufactured assemblies.

Toner paddle - one of the great complaints about toner supplies is that the toner is not always distributed evenly along the development roller. While this is not an issue while the toner is relatively new, a cartridge that is approaching exhaustion may experience faint streaks in the print where toner is particularly low. Newer toner/engine designs include a toner paddle that circulates the toner supply. This serves two important purposes; it keeps the toner from clumping due to age and humidity, and it keeps the toner level steady across the development roller.

New toner formulations - even the toner itself has undergone some substantial improvements over the last few years. Remember that toner is a microfine powder composed of plastic, iron, and coloring. As the resolution of an EP printer increases, the size of a toner granule becomes a gating issue - after all, a grain of toner must be smaller than a single "dot" - otherwise, fine detail will be lost. Toner is continuing to improve in the remanufacturing market as well, but its overall quality still lags the original manufacturer’s toner.

The disassembly and reassembly of most printers is not terribly difficult, but it often requires a bit of finesse to overcome the variety of plastic latches and screws that hold the units together. Carriage-type printers are fairly straightforward in their use of enclosures and internal assemblies. Be careful to note the location of each screw, since virtually all printers (carriage and page) tend to mix and match screw lengths to accommodate tight space limitations (especially with the internal assemblies). As with any electro-mechanical disassembly, be very careful to denote the location and orientation of each connector as you remove it. Make a reference mark with an indelible marker if necessary. When working with mechanical assemblies, try to replace at the sub-assembly level wherever possible. Printer mechanics are relatively precise configurations - if critical tensions or dimensions should change during a repair, the mechanism may never work satisfactorily for your customer. Page printer mechanical assemblies are unusually unforgiving. When electronic assemblies must be removed or replaced, be sure to follow good static precautions to prevent accidental damage to the board(s).

NOTE: Be sure to unplug the printer and allow ample time for the power supply (or supplies) to discharge before attempting to open the enclosure. High-voltage supplies are especially dangerous, and can result in a nasty shock if not allowed to discharge.

NOTE: Impact print heads can become extremely hot during long printing sessions. Allow plenty of time for the print head to cool before attempting to remove or replace the impact head. Fusing assemblies in EP printers also reach over 200° F during normal operation. Even when opening the EP printer for routine maintenance, allow ample time for the fusing unit to cool before reaching inside.

When reassembling a printer, pay close attention to the way each sub-assembly fits together. As with notebook PCs, printer manufacturers try to make every cubic centimeter count. If assemblies are not seated and secured properly, the printer will probably not work right. This consideration is especially important for all types of EP printers. Be careful to route cables and connectors properly. A loose or improperly seated cable can wreak havoc with the printer. Pinched or sliced cables can also impair the printer. Re-assemble the printer, but do not install the upper enclosure(s). Run a self-test or other diagnostic to check the printer thoroughly. If a problem remains, leaving the upper housing off will make another disassembly that much easier. If the printer checks properly, secure the upper housing(s) and run the self-test or third-party diagnostics again as a final test before returning the printer to service.

Printers are generally regarded as rugged and reliable devices - they have to be in order to handle the wide variety of printing demands placed on them by today’s PC users. Still, the following points will help you get the most from your printer, and minimize potential problems during service:

• Fuser assemblies and print heads get hot during normal operation. Be sure to allow plenty of time (at least 15 minutes) for the printer to cool before attempting any sort of service inside.
• Keep the printer assembly clean. Vacuum out any accumulations of dust, debris, or toner which you may find in the printer.
• Keep the paper path clear. Paper and label fragments (or other foreign matter) can easily interfere with paper as it passes through the printer.
• Do not use harsh chemicals when cleaning the printer case. Use only diluted ammonia and water on a clean cloth to wipe the printer’s enclosures. Never spray cleaner directly onto the enclosures.
• Keep the paper rollers clean. Paper handling rollers are prone to problems with age and wear. Eventually, the roller(s) may no longer handle the paper correctly. Whenever working inside a printer, make it a point to clean the paper handling rollers.
• Pay close attention to screw lengths and locations to ensure that you can reassemble the printer properly.
• Use fresh, good-quality, standard weight paper. Printers can be notoriously picky about unusual paper weights and finishes, so be sure that the paper can be handled adequately by the printer. Humidity can also effect print quality, so be sure that paper is fresh and dry.
• Recycle ink and toner cartridges. Recharging toner and ink cartridges is often much cheaper (and more environmentally friendly) than simply discarding the spent cartridges. However, don’t experiment with different media - refill the cartridge only with media approved for the particular cartridge.
• Keep the ink cartridge covered. Ink will eventually dry out and clog the nozzles of an ink cartridge. Be sure that the ink covering/cleaning system is working on your printer.
• Keep toner distributed. Toner tends to thin out in some areas of the cartridge before others. Shake the toner cartridge periodically to keep the toner evenly distributed.
• Conserve toner by keeping the image intensity set to a minimum acceptable level, and use lower resolutions for "draft" work.

That’s it for Chapter 5. Be sure to review the glossary and chapter questions on the accompanying CD. If you have access to the Internet, try out some of the web contacts below:

Alps: http://www.alpsusa.com/cgibin/var/alpsusa/index.html

Automation Consulting and Supply: http://www.oddparts.com/ink/inkjet.htm

Epson: http://www.epson.com/home.shtml

General Printer Newsgroup: comp.periphs.printers

Hewlett-Packard: http://www.hp.com/cposupport/eschome.html

Ink Roll: http://www.inkroll.com/eindex.html

Lexmark: http://www.lexmark.com

Raven Systems: http://pw2.netcom.com/~jcohl/small.html

Refilling Tips: http://www.missupply.com/concern.html

Toner Charge: http://www.tonerrecharge.com/