CIS 107a: Introduction to Hardware Concepts

Chapter 12: Supporting Printers and Scanners



This chapter discusses printers, scanners, and resolving problems with both. The objectives important to this chapter are:

  1. How printers, including laser printers and ink-jet photo-quality printers, work
  2. Installing printers and scanners and sharing them on a network
  3. How to support and troubleshoot printers

The chapter begins with a discussion of ways to "physically" attach to a local printer. You should be aware of all of the standard media connections: parallel, serial, USB, FireWire, network cable, and SCSI. Some printers are also accessible by infrared, WiFi, or Bluetooth wireless connections.

The chapter continues with a good discussion of how laser printers work. It has been reported by students taking the A+ certification test that questions on printer troubleshooting are common, so this chapter is an important one to study.

There are six processes listed that take place when a laser printer prints:

  1. Cleaning - the drum, a rotating barrel in the printer, is cleaned of toner, and cleared of any electrical charge.
  2. Conditioning - the drum is given a strong electrical charge. The example in the book indicates a charge of -600 volts.
  3. Writing - a laser changes the charge on the drum everywhere toner is meant to go. (Toner becomes ink. See below.) The charge may be -100 volts. This change effectively puts an electrical version of the print image on the drum. The change takes place only in areas that correspond to characters or images to be printed. The image on the drum is a mirror image of what is intended to print.
  4. Developing - toner is given a charge in between the two charges listed above. Let's say it's about -500 volts. This charge is close enough to the -600 volts that areas with a -600 volt charge repel the toner. However, it is different enough from the -100 volt charge that the image areas on the drum attract the toner. Electrical differences are relative, after all. The drum is supplied with toner and low voltage image areas become coated with it.
  5. Transferring - a piece of paper is given a strong positive charge, which attracts the toner more than the weak negative charge of the image on the drum. This charge is often reduced a bit, so that the paper does not stick to the drum. The paper is passed close to the surface of the drum, and the toner transfers to it. Because the drum rolls along the paper, the image made by the toner is transferred to the paper. Because the drum held a mirror image of the intended print job, the toner now shows the intended image on the paper.
  6. Fusing - the paper, now having toner on it, passes through heated rollers, which fuse the ink and plastic toner to the paper. This makes the image on the paper more permanent, and minimizes smearing.

It is possible to carry out the processes above by reversing the charges involved. The principle works either way.

The process above describes how a monochrome printer works. A color laser printer follows a similar process, but it uses four different colors of toner, so the Writing step takes place four times, each time placing a different color component of the image on the drum. Color laser printers generally use the CMYK color system (see below).

Common problems with laser printers are described:

  • If the output is faded, smeared, wavy, speckled, or streaked, you may be low on toner. Try shaking the cartridge to prolong its life. Replace the cartridge with a new one if possible.
  • Paper will not perform well if it is too hot, too wet, too dry, too thick, too thin, or simply the wrong kind of paper. Do not open packages of paper until you are ready to use them. Do not store the paper where it can become damaged by heat or moisture. Use fresh paper, of an appropriate type for the printer.
  • Paper jams often occur in laser printers. A technician servicing such a printer should become familiar with the path that paper is meant to follow through the printer, and should be able to troubleshoot that path for shreds of paper that can clog it.

Ink jet printers are discussed for a few pages. Dots of ink are sprayed onto a sheet of paper. There is no fusing necessary, as the ink generally dries quickly.

Some ink jet printers use only one color of ink, while others use multiple tones to create color output. Typically, color ink jet printers use the CMYK system of printing, mixing separate amounts of Cyan, Magenta, Yellow, and Black ink to make other colors.


Some ink jet printers do not have a separate black ink supply, but simulate black by combining other colors. This sort of printer is known for lower quality output.

The size of the dots of ink can vary greatly from one model of printer to another. Smaller dots give greater resolution. If a printer has the ability to vary the size of the dots, this can make the output much smoother.

Servicing an ink jet printer is often accomplished by using software to align the output of the print head, to blow out a clog in one or more jets, or to simply inform the device that an ink cartridge has been replaced. Older models required manual cleaning of the print head.

It is important not to leave an ink jet printer turned on indefinitely. This will reduce the life of the print head and dry out the ink supply. It is also important to use the correct type of paper to avoid smears, poor print quality, and other problems.

Dot matrix printers are not used much any more. They work by having a series of pins in the print head hit an ink-soaked ribbon, which leaves a mark on a sheet of paper on the other side of the ribbon. The print head moves back and forth horizontally, while the paper advances on a roller vertically. The only advantage that they have at this time is that they are useful when printing on actual carbon forms. Laser and ink jet printers can produce multiple copies of output, but they cannot be used to print on a form that is several carbon copies deep. Output from dot matrix printers is grainier and less appealing than output from laser or ink jet printers. Service is expensive compared to the cost of simply replacing a dot matrix printer that has worn out.

The text discusses troubleshooting printing, suggesting that you should try to isolate a problem into one of four areas:

  • Problems with the application that you are printing from are indicated if you can print from a system prompt or other application, but not from the one you want to use. Determine if the application is installed properly, and if it is supposed to support your printer. Some applications only print to the default Windows printer. Is your printer set as the default?
  • Problems with the Operating System or printer driver can be indicated if you cannot print from a system prompt, but can print a test page by pressing a button on the printer. Check online for a newer driver, or a driver compatible with your OS. Try deleting the printer from Windows list of printers, then installing service to it again?
  • Connectivity problems, such as a bad cable or port, can also be indicated if print jobs do not come out, but you can print a test page on the printer by pressing a button on it. Try swapping out printer cables with one that is known to be good. Try checking the state of the port: is it in the right mode for your printer? EPP? ECP? Bi-directional?
  • Problems with the printer itself are indicated if none of the above is possible. This category includes being out of ink or toner, paper jams, wrong paper, too much heat or humidity, and other problems.

Scanners are described as falling to three types:

  • flatbed scanners - Usually, this type give the best quality output, scanning one page at a time, and giving the user the opportunity to scan again with different settings.
  • sheet-fed scanners - This type provides the best performance if you need to scan many pages at a time, and are satisfied with standard output.
  • portable scanners - This type includes handheld scanners and small scanners that can be fed a page or receipt at a time.

Print services are the main reason that networks exist. They are also the service most complained about on networks. The text presents three basic ways to attach a printer to a network:

  • A printer may be cabled to a workstation that is itself attached to the network. The printer can then be shared as a network resource. The drawback is that each print job places a burden on the workstation, and the printer is unavailable unless the workstation is logged in to the network.
  • A printer that is equipped to connect to a network can be directly connected. Some printers have their own NIC, some can have one installed.
  • An interface between the printer and the network can serve as the actual connection point. Hewlett Packard makes a product called the HP JetDirect card, which can be used to connect printers to networks. (Printers that use an HP JetDirect card do not have to be HP printers.)

Windows workstations commonly contain the proper software to share local printers. (As mentioned in the first item above.) This is a quick and easy thing to do, but it suffers from the problems noted above, and it does not work well for large networks.

To share a local printer:

  1. First install it on one PC.
  2. If running XP, under Printers and Faxes, open the Properties window for the printer. Choose the Sharing tab, and give the printer a name so it can be shared.
  3. If other computers will run other operating systems, install other drivers for the printer by clicking Additional Drivers.

The PCs that will share the printer must belong to a defined Workgroup, which means that you need to configure each PC to be a member of the workgroup, and most important, they must be connected through a common network environment. This can mean that they all connect to a switch through Ethernet connections. A server is not required, but sharing a printer this way means that for any computer in the workgroup to print to it, the computer that is actually connected to the printer must be running.

A short list of troubleshooting ideas is presented, mostly having to do with shared printers. I will adapt the ideas here to apply to actual network printing.

  • Is the printer online? It is surprising how many people expect a device to work that has not been turned on, or has not be set to "on line" mode.
  • Is the network printer configured correctly on the PC? This means, have you installed the correct driver, are you sending print job in the right language, for the right size paper, etc.?
  • Is the correct network printer selected? Many users will send a print job and not be aware that they sent it to the wrong printer.
  • Is there enough hard disk space available on the PC? When preparing a print job to send, a workstation must compose it as a temporary file. If the workstation does not have enough room for the file, the print job will either fail or be incomplete.
  • Can you print successfully from another application? If so, the problem is likely related to your installation of the problem application. It is possible that the application cannot print to this sort of printer.
  • Can you print successfully from the host PC using the identical application? This applies to shared printers. It is not really diagnostic unless the two workstations are alike in all ways.
  • Can you print to a file and then send the file to the host PC to successfully print? If this works, then the problem is with data transmission. If this does not work, then the problem is with the application or print driver on the remote PC.
  • For DOS applications, you may need to exit the application before printing occurs.