Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s ManualChapter 20
Chapter 20
Printers
Learning Objectives
This lesson will show you how to install, use, and troubleshoot printers. By the end of the lesson, you should be able to do the following:
- Describe current printer technologies
- Explain the laser printing process
- Install a printer on a Windows PC
- Recognize and fix basic printer problems
Pre-Test
1.Does a laser printer actually use a laser?
2.What’s the most popular connection for a printer?
3.What kind of a printer works best with multiple copies (carbon paper)?
4.What printer heats ink as part of the printing process?
5.What is the laser printing process?
Lecture Outline
Essentials
I.Printer technologies
A.The A+ Certification 220-604 Depot Tech exam stresses printing and expects a high degree of technical knowledge about the functions, components, maintenance, and repair of all types of printers. Other exams don’t hit it as hard on printers, but they do require students know much of the information in this chapter.
B.Modern printers can be categorized intosix major types: impact, inkjet, dye-sublimation, thermal, laser, and solid ink.
C.Impact printers
1.Impact printers work by striking an ink ribbon to transfer ink to paper, much like a typewriter does. While daisy wheel printers have largely disappeared , impact printers still exist in many offices, in point of sale (POS) equipment, and some specialized business applications using multipart forms.
2.Impact printers are the only printers that can print to multipart forms (carbon paper and carbonless papers).
a)Dot matrix. Dot matrix printers use a grid or matrix of tiny pins, called a print head. Dot matrix works because the printer BIOS interprets a stream of text coming from the PC as a raster image (as a monitor does), and then paints the image as the data flows over the print head. The pins are shot out of the print head and impact an ink ribbon, which transfers a letter or other image in the form of tiny dots to a paper, also supported by a platen.
b)Most print heads have 9 pins and produce draft quality output, or 24 pins that produce letter quality or near-letter quality (NLQ) output. Naturally, the more pins, the higher the quality of the output produced.
D.Inkjet printers
1.Also called ink dispersion printers.Inkjet printers have a printhead mechanism, support electronics, transfer mechanism (to move the printhead back and forth) and a paper feed component. Ink is ejected through tiny tubes by one of two methods.
a)The heat method heats up a tiny amount of ink to boiling point and ejects a droplet of inkonto the paper.
b)Some inkjet printers use a mechanical method.
2.Older inkjet printers used two cartridges, one with black ink and the other one with three colored inks combined (cyan, magenta, and yellow). Today, it is more common to have separate cartridges for each of the colored inks: cyan (blue), magenta (red), and yellow.
3.Inkjet printers have two key features:
a)Resolution, measured in dots per inch (dpi). The higher the resolution, the better the quality of the output.
b)Print speed, measured in pages per minute (ppm)
4.Inkjet printers today can print to a wide range of media,including photo papers, iron-on transfers, optical disks, or even fabric
E.Dye-sublimation printers
1.Sublimation means to cause something to change from a solid form to a vapor and then back into a solid. This process is what dye-sublimation printers use. Also called thermal dye transfer, these printers are limited to photo printing, high-end desktop publishing, and other applications where fine detail and rich color are important.
2.Using the four color or CMYK (cyan, magenta, yellow, black) method, these printers use a roll of heat-sensitive plastic film and a printhead with heating elements that, when moved across the film, vaporizes the dyes causing them to soak specially-coated paper.
3.This process requires one pass per page for each color. The resulting images are a continuous tone, so each pixel is a blend of the different dye colors. (Other printing technologies produce dithered images where single-color dots simulate blended colors.)
4.For high-quality color output that rivals a professional photo lab, you can’t beat the dye-sublimation printer, but the printer itself and the special paper are both expensive.
F.Thermal printers
1.Two kinds of thermal printers are the direct thermal printer and the thermal wax transfer printer.
a)Direct thermal printers use a heated print head to burn dots into the surface of special heat-sensitive paper. These printers are commonly used for printing receipts in retail businesses.
b)Thermal wax transfer printers use film coated with colored wax that is melted by the print head.
2.Both kinds of thermal printers can use regular paper, making them cheaper than dye-sublimation printers, but the output isn’t quite as good because of color dithering.
G.Laser printers
1.Using electro-photographic imaging, laser printers produce high-quality and high-speed output of both text and graphics. Laser printers rely on the photoconductive properties of certain organic compounds.
2.Laser printers have many critical components, including the following:
a)A toner cartridge supplies the toner to create the image on the page. All modern laser printers have a single toner cartridge. This replaceable cartridge contains all the user-replaceable parts in one package. These parts, such as the toner and photosensitive drum, need to be changed from time to time anyway, so they are designed to be replaced by the user in a single step, thus reducing maintenance costs.
b)The photosensitive drum is an aluminum drum coated with a photosensitive compound. The drum is grounded (via the power supply), but the coating is not. When light hits the coating, the drum allows the charge to bleed to ground. Any marks or defects on the surface of the drum will transfer toner to every sheet of paper.
c)The erase lamp wipes the entire drum by bathing it in light. The coating then bleeds the charge to the drum (which releases it to ground). The coating is then electrically neutral.
d)The primary corona is a thin and delicate wire, located very close to (but not touching) the drum. When high voltage passes through the wire, an electric field (or corona) forms. The corona then charges the photosensitive coating with a negative charge on the drum, giving its entire surface a uniform charge between ~600 and ~1,000 V. The primary corona is often built into the toner cartridge, but not always. If the wire is in the printer instead, keep in mind this wire is very delicate. The manufacturer should provide a special brush for cleaning it when you replace the cartridge.
e)The laser shoots out a highly focused light beam that acts as the writing mechanism. This laser beam strikes the drum and paints an image. The entire surface of the drum gets a uniform negative charge between ~600 and ~1,000 V after being charged by the corona. Where the laser strikes the drum, the charge reduces to about ~100 V.
f)The toner is a very fine powder of plastic particles bonded to iron particles. The toner is charged negatively between ~200 and ~500 V. The toner is attracted to the areas on the drum hit by the laser, holding roughly 100 V.
Discussion Point
Toner
Toner is nasty! It is a very fine powder that seems to jump onto your new dress shirt from across the room! It gets into everything. Fortunately, it is relatively easy to clean up—just a damp cloth or paper towel will collect it. However, it is nearly impossible to get out of clothing. Also, many governments consider it a hazardous waste, not to be thrown in the trash. Many companies recycle toner. Please check with your local authorities for disposal methods.
g)The transfer corona applies a positive charge to the paper as it goes through the printer. The negatively charged toner, already on the image areas on the drum, is attracted to the positively charged paper. After the toner is transferred to the paper, the static charge eliminator removes the charge from the paper to prevent it from wrapping around the drum.
h)The fuser assembly applies heat (roughly 300–400 degrees Fahrenheit or 148–204 degrees Celsius) to the top of the paper via a Teflon-coated roller, pressing the paper against a pressure roller. The heat melts the toner and fuses it to the paper. Otherwise, the toner would just blow away.
i)Laser printers have two separate power supplies. The primary power supply supplies power to the motors that move the paper, the system electronics, the laser, and the transfer corona. The high-voltage power supply provides power to the primary corona. It is very dangerous. Never work inside a laser printer when it is turned on.
Safety Alert
Because of the high voltage present in a laser printer, you should unplug it—even before changing toner cartridges.
j)Numerous turning gears perform mechanical functions in the laser printer, including moving the paper, turning the roller, moving the mirror and laser, and evenly distributing the toner.
k)Laser printers contain at least one electronic system board with a processor, ROM, and RAM for storing the image before it is printed. Some printers divide these functions among more than one board. If the printer does not have enough RAM, you may get a memory overflow error. You may be able to upgrade the RAM using generic DRAM,similar to that in your PC.
l)To prevent damage to the printer components, most laser printers have an ozone filter to remove the ozone generated by the corona. Although ozone is not harmful to us, you may “smell” it around a running laser printer. You may need to vacuum or replace this filter.
m)A number of sensors and switches are located throughout the printer that warn you of paper jams, empty paper trays, low toner level, and other problems. If they break or are too dirty, they may generate false signals.
H.Solid ink printers
1.Use solid sticks of non-toxic “ink” that produce more vibrant color than other methods. Ink is melted and then absorbed into the paper.
2.The cost of solid ink printers is substantially higher than the cost of inkjet printers. The cost of consumables (solid ink sticks vs. ink cartridges), however, is significantly less.
I.Printer languages
1.Printers need a specific language to tell them how to create a graphic image or text. There are several languages in use.
a)American Standard Code for Information Interchange (ASCII). Among the letters and characters used in ASCII, there also exist command codes. These codes control common printing tasks such as carriage returns, line feeds, and form feeds. ASCII is not a very good language for printing anything other than basic text.
b)PostScript. Developed by Adobe, PostScript uses page description language (PDL), which is capable of producing high-resolution graphics and scalable fonts. It is also the first printer language to be totally printer independent. Because PostScript is understood by printers at a hardware level, the majority of the image processing is done by the printer and not the PC’s CPU. Because they are printer-independent, you can print a PostScript file to a file instead of a printer. You can then take that saved file to any PostScript printer, on any platform, and print it out.
c)Printer control language (PCL). Developed by Hewlett-Packard, PCL is more advanced than ASCII in that it has more printer controls, but it still cannot handle graphics.
d)Windows graphical device interface (GDI). Windows uses the GDI portion of the operating system to handle print functions. GDI uses the PC’s CPU, instead of the printer, to process the image. GDI converts the page to bitmap and sends it to the printer. Even text sent to the printer appears to the printer as an image, not as text.
J.Printer connectivity
1.Printers connect by either a parallel port or a USB port.
2.Parallel communication and ports have been available since the original IBM PC. Although faster than serial ports, parallel ports are slow, with a maximum data transfer rate of about 150 kilobytes per second (KBps). Standard parallel ports lack bidirectional capabilities.
3.The IEEE 1284 standard defines a high-speed bidirectional parallel port with backward compatibility.
a)IEEE 1284 requires the following:
(1)Support for five modes of operation, including compatibility mode, nibble mode, byte mode, EPP, and ECP.
(2)Standard method of negotiation for determining which modes are supported
(3)Standard physical interface
(4)Standard electrical interface
4.Although not officially a standard, parallel cables typically have a male DB 25-pin connector on one end and a Centronics connector on the other.
a)These cables are limited to less than six feet and may not be used for ECP or EPP operations.
b)For more reliability, an IEEE 1284–compliant cable is used.
5.USB printers
a)USB printers plug into the USB port using a special USB cable. One end has a type A connector, and the other has a smaller type B connector.
6.FireWire printers
a)Just as easy to use as USB ports and cables. FireWire printers are also hot swappable and hot pluggable.
7.Network printers
a)Printers can be on the network. Typically, they have an onboard NIC, a standard RJ-45 Ethernet connector, and an assigned IP address (either statically or dynamically assigned from DHCP).
b)Printers can also be connected to print servers and then be available as network printers.
8.Other printers. Lots of other types of connections are possible, such as serial or SCSI. The connections you’ll most likely see, however, are parallel, USB, FireWire, and networked connections.
IT Technician
II.The laser printing process
A.The laser printing process usually involves six physical steps.
Discussion Point
Charges
Remember the phrase from high-school science class, “opposites attract”? That is the underlying principle behind laser printers. The toner jumps around from one place to another based on the positive or negative charges it is following. The negatively charged toner seeks out and jumps to the positively charged paper.
1.Clean the drum. A rubber blade scrapes the drum of any excess toner, and erase lamps neutralize the electrical charge on the drum.
2.Charge the drum. The primary corona wire places a uniform negative charge on the entire surface of the drum. The charge is usually between ~600 and ~1000 V.
3.Writethe image. The laser light source then writes the image to the drum, which changes the charge of the written areas to a lesser charge (negative in relation to the charge of the drum).
4.Develop the image. The toner is attracted to the areas of the drum hit by the light, creating a developed image.
5.Transfer the image. The transfer corona charges the paper with a positive charge. The negatively charged toner still on the drum leaps onto the positively charged paper. At this point, the toner merely sits on the paper.
6.Fuse the image. Finally, for the process to be complete, the toner needs to be fused to the paper. The paper passes through two rollers. The bottom roller, the pressure roller, presses the paper to the top roller, the heating roller. The heating roller is coated with a nonstick material and brought to a high temperature. This high temperature melts the toner, which fuses to the paper.A static charge eliminator removes the positive charge from the paper to prevent it from wrapping around the negatively charged drum after the toner has moved to the paper.
Discussion Point
Mnemonic
The A+ exam expects students to know the steps of the laser printing process in order. To help students remember the laser printing process order—Clean, Charge, Write, Develop, Transfer, Fuse, try this mnemonic: California Cows Won’t Dance The Fandango. It may sound silly, but it works!
B.The electronic side of the process
1.Selecting “Print” causes the CPU to process the request, but it’s often not sent immediately to the printer; instead, it’s sent to the print spooler, which allows you to send multiple print jobs to the printer.
2.Raster images. Laser printers generate a raster image or a pattern of dots of the entire page and then “paint” it on the drum. The raster image processor (RIP) chip translates the raster image into commands to the laser. This process uses memory (RAM) to store an entire page. If there is not enough RAM to hold the data for the entire page, you will get a memory overflow (MEM OVERFLOW) error. Making the graphics smaller or reducing the resolution may allow the page to print. A better long-term solution is to add more RAM to the laser printer.