Section Objectives
After you complete this section you will:
Understand the different categories of printers.
Understand what DPI is.
Identify the parts of a laser printer.
Memorize the laser printing process.
Understand laser printer preventative maintenance goals.
Identify inkjet printers.
Identify dot matrix printers.
Identify printer connections and configurations.
Printers are an area of importance on the CompTIA hardware exam. This section of the tutorials explains the different types of printers, the parts of a printer you should be aware of, and troubleshooting techniques for printers.
This portion of the tutorial will teach Domain 5.0: Printers, which accounts for 10% of the exam.
Topics recommended for study by CompTIA are:
- Identify basic printer concepts, operations, and components
- Types of Printers: Laser, Inkjet, Dot Matrix
- Paper feeder mechanisms
- Printer connections and configurations: parallel, network, USB, infrared, serial
- Identify service techniques with common printers
- Identify common problems with printers: feed & output, errors (printed and displayed), paper jam, print quality, safety precautions, preventative maintenance
Basic Types of Printers
In your career as an IT technician, you will troubleshoot and work with a variety of printers: laser printers, inkjet printers, dot matrix printers, label printers, plotters, photo printers. Luckily, the troubleshooting techniques and issues are similar among many varieties of printers, allowing you to transfer your knowledge of printers from one brand to another, and often from one type to another.
DPI
One of the common indicators of a printer’s print quality is the DPI the printer prints at. DPI is an acronym for Dots Per Inch.
The quality of the print is represented by how many dots per inch across the page and how many dots per inch down the pager.
For example, in a recent ad I saw for Canon S300 inkjet printer, the resolution for black ink was 600 x 600 DPI, while the resolution for color was 2400 x 1200 DPI. As the printhead travels across the page, its best resolution is printing up to 600 dots of black ink per inch and 2400 dots of color ink per inch.
Laser Printers
In most office environments, laser printers have become the most common type of printer. A laser printer (also called a “page” printer) receives its print information a page at a time and prints using a combination of lasers, electrostatic charges, and toner.
Parts
The laser printer has several parts which make up a significant portion of its operation: toner cartridge, laser scanning assembly, high voltage power supply, DC power supply, paper transport assembly, transfer corona assembly, fusing assembly, formatter board.
The toner cartridge holds the toner which is what is “printed” onto the page. Toner is sensitive to the electrostatic charges. The toner cartridge also contains the print drum, charge corona wire, and the cleaning blade. The print drum has a photosensitive material on it which holds static charge when it is not exposed to light. The charge corona wire charges the drum, while the cleaning blade does exactly what the name suggests, it cleans the used toner off the drum.
The laser scanning assembly holds the laser which shines its light on certain parts of the printer drum. The electrical charge is reduced and the toner attaches itself to the drum where the laser has shined.
The high voltage power supply takes 120 V AC and converts it to higher voltages for the charge corona wire and transfer corona wire. The DC power supply products +5 Volts DC, -5 Volts DC, and +24 Volt DC from household current.
The paper transport assembly moves the paper through the printer. It is a series of motors and rollers to move the paper.
The transfer corona assembly charge the paper with a posit
ive charge as it moves through the printer. Once charged, it picks up the toner from the photosensitive drum.
The fusing assembly (also known as the “fuser”) applies pressure and heat to the paper to seal the toner particles to the paper. In the process of fusing, there is a halogen lamp which heats up to about 350 degrees F.
The formatter board is the circuit board that controls everything that is going on in the printer. It formats the information then tells the different modules to function together to get the printer page across.
Laser Printing Process
Once a laser printer receives the print information from the PC (or sometimes from a file server), it goes through a certain process in order to print:
1. Cleaning
2. Conditioning
3. Writing
4. Developing
5. Transferring
6. Fusing
This process is important to learn and understand as there is guaranteed to be a question regarding this information on the exam:
1. Cleaning – the EP drum is cleaned with a rubber blade.
2. Conditioning – the EP drum is given a negative charge of about -600 Volts by the primary corona wire.
3. Writing – a laser beam writes to the EP Drum. This laser causes portions of the drum to become almost positively charged.
4. Developing – toner is applied to the drum by the particles being transferred to the areas of positive charge.
5. Transferring – the Transfer Corona wire charges the paper with a positive charge, the EP drum turns the paper as it runs beneath.
6. Fusing – the paper runs through the Fusing Assembly which is heated to 350 degrees F. The toner is fused onto the paper.
This printing process will be in one or more questions on the exam. Memorize it!
Preventative Maintenance
The purpose of preventative maintenance on a laser printer is to prevent potential problems from appearing. There are several things you can do in preventative maintenance.
The ozone filter should be replaced during maintenance.
The rollers inside the printer may need to be cleaned/replaced. There are roller replacement kits available for most major brands of printers. The replacement roller kits should be replaced by a professional with experience in laser printers.
Always fan paper before inserting it into the printer tray. This allows separation of the individual sheets of paper to decrease chances of a paper jam from the paper tray.
Troubleshooting Techniques
Dark spots on the paper could indicate loose toner particles. Run a few papers through the printer to clear it up.
The transfer corona can cause the print to be too light.
Always check the leading edge of paper when there is a paper jam, it can indicate what part of the printer is causing the jam.
Things to Remember
The drum is photoconductive and loses its charge when light hits it. It is normally negatively charged during the print process.
The primary corona has the highest negative charge in a printer.
A Word About LED Printers
A less common type of laser-quality printer is an LED printer. An LED printer uses LED light (Light Emitting Diodes) in place of a laser. The A+ Hardware exam probably will not even have a question regarding LED printers, though for your career, you should be aware of it.
LED printers are less expensive to manufacture than laser printers, though a recent search at a major computer reseller only turned up three LED printers, all by Oki.
Inkjet Printers
Inkjet printers are a very common type of printer because of their low cost and color capabilities.
Inkjet printers functioning by spraying ink onto paper to form the letters and graphics. The inkjet printer has an ink cartridge (or sometimes several ink cartridges) which contain several chambers of ink. When the ink runs out, you must replace the ink cartridge. It is not recommended you refill ink cartridges.
Most common inkjet printers today are bubblejet printers, a spin-off from the original inkjet printers. Since the term inkjet is in much more common use, the printers are still referred to as “inkjet” printers.
The original inkjet printers used a pump and ink nozzles to “spray” ink onto the page. Bubblejet printers use a special ink cartridge which has a tiny pinhole in the bottom. When the printer needs a certain color ink, it sends an electronic signal to a heater element near that color. It heats the ink up near vapor and as the ink expands, it sends a drop out the pinhole in the bottom which the print head applies to the page as it passes.
You may have noticed in inspecting a inkjet printer that the printhead always “rests” in the same location when not in use, and commonly goes through some iterations prior to printing. When it moves out of the print range and rests, it rests on a specially designed pad to soak up any excess ink and keep the printhead always ready to print. The iterations you hear it performing prior to printing are related to cleaning to ensure the printhead is clean prior to applying ink to a page.
Dot Matrix Printers
The major category of printers you will need to be aware of for the A+ Hardware exam are dot matrix printers. Dot Matrix printers are a form of impact printer. The printhead in a dot matrix printer is a series of pins which form numbers, letters, and graphics as it passes over the paper. In early Dot Matrix printers, 9-pin was a common size of the printhead. This was referred to as a “draft quality printer.” Later versions, such as the 24-pin printhead, print in near letter quality (NLQ) print mode.
A dot matrix printer works by striking pins inside the printhead against a ribbon as it passes in front of the paper. These pins form letters, numbers, other characters, and graphics.
Things You Need to Know
During preventative maintenance, never lubricate the printhead of the printer.
A tight ribbon could be the cause for flecks and smudges on the paper.
A missing or broken printhead pin could cause incomplete printing.
If the print density is erratic, there can be a problem in the advancement of the printer ribbon.
Types of Printer Connections and Configurations
There are several connection methods for printers:
• Parallel
• Network (commonly Ethernet)
• USB
• Infrared
• Serial
• Firewire
• JetDirect/Print Server Box
The most common connection type for personal printers is a parallel type of connection, though USB is gaining in numbers for personal printers.
Printer Connections
Network, or commonly Ethernet, connections are commonplace on network laser printers, though some other types of printers do employ this type of connection. Generally, network printers are designed to be shared using a central file/print server, though you can share them off a workstation in a “workgroup” environment.
Parallel is the original standard for printers and a lot of basic printers still rely on the parallel port connection. A parallel (also called LPT port) sends and receives data simultaneously, transmitting data in parallel. Parallel uses a DB25 connection on the computer side and a oddly shaped 36 pin connection on the printer.
USB, or Universal Serial Bus, is a very common connector type for personal printers being sold today. USB is sold as the next generation of standard ports for computers. USB allows mice, keyboards, scanners, printers, most peripherals to connect to a computer. It supports up to 12 Mbps transfer rate and is hot swappable.
Infrared is not very commonly used. An Infrared acceptor
allows your devices (laptops, PDAs, Cameras, etc) connect to the printer and send print commands via infrared signals.
Serial allows your printer to connect to your computer via the serial port.
Firewire is a high speed connection commonly referred to as IEEE1394, its “standard”. Though not specifically mentioned in the preparation outline for the exam, you should be aware that a printer may connect via Firewire. Firewire is a high speed connection typically used for digital video editing or other high bandwidth requirements.
An HP Jetdirect (or Printer Server Box) is a device which allows a non-networkable printer to be networked. For example, we have an Epson color inkjet printer in our office which has a standard parallel port connection on it. The JetDirect box allows the printer to be connected into our network and allows the printer to be shared off of our file/print server.
After studying this section you should:
Understand the different categories of printers.
Understand what DPI is.
Identify the parts of a laser printer.
Memorize the laser printing process.
Understand laser printer preventative maintenance goals.
Identify inkjet printers.
Identify dot matrix printers.
Identify printer connections and configurations.
