There are several questions on the A+ exam about how laser printers work, but few technicians are called upon to service them in everyday life. In this first part of a two-part Daily Drill Down series on laser printers, I will explain how laser printers work and some ways to identify and correct problems. This can help you troubleshoot laser printer problems in your organization, as well as prepare you for the printer theory portion of the A+ exam. Be sure to watch for part two of this series where I’ll cover Postscript, interfaces, fonts, driver settings, and various other aspects of laser printing.
How does a laser printer work?
In the beginning, there was the impact printer (dot matrix or daisywheel). Almost everyone understood this type of printer because it was just like a typewriter. Something hard struck an inked ribbon and made a mark on the page. Then came the inkjet printer, which was only a little bit more complicated: Ink squirted out of a nozzle onto the paper.
Laser printing, however, involves a multistep process, and what’s happening is not obvious from watching the printer operate. Many end users (and even some technicians) see it as mysterious activity. Paper goes in blank; paper comes out printed. But how does it happen?
If any of you still remember mimeograph machines, their operation provides a rough analogy to a laser printer’s. The entire page on a mimeograph was printed on a master sheet that clung to a rotating cylinder. As you turned the handle, the cylinder rotated past ink and paper, transferring the image to the document. Laser printers work much the same way. The main difference is that the image on the laser printer’s cylinder is created with lasers and electrical charges.
Step 1: Incoming data
First, the computer sends data to the printer. But it doesn’t just barrel ahead—it queries the output port to make sure a printer is attached and ready. The printer sends a signal back on the strobe line (pin 1) for parallel or DTR (line 20) for serial interface, indicating it is ready for data.
Next, if the print job needs any fonts that the printer does not have in residence (such as TrueType fonts), those are sent to the printer and stored in its memory. Then, the print job itself is sent and stored. If the job is larger than the printer’s memory can accommodate, the OS either waits (as with single-tasking OSs such as DOS) or uses its own print spooler to feed the remainder of the job to the printer (as with Windows). Some printers come with their own custom software that includes a print spooler that takes over instead of the one in the OS.
Laser printers fall under the category of page printer because they compose the entire page in their memory and then transfer it to paper. A full page with graphics occupies on average 512 KB of memory, so a decent laser printer should have at least 1 MB of memory to store at least one page plus any associated fonts. Printers with more memory can hold multiple pages of a print job in their memory, which offloads the print job more quickly from the OS.
Step 2: Drum preparation
The single largest part of the laser printer is the drum, an aluminum cylinder coated with photosensitive material. In preparation for printing, the drum must be cleaned to remove any traces of previous pages. First, a rubber blade wipes the excess toner from the drum, and then erase lamps (in older models) or a charged drum (in newer models) electrostatically clean it by neutralizing residual electrical charges on it.
The drum’s photosensitivity can be damaged by exposure to light, so erase lamps are red-filtered. On some models of laser printers, red plastic is placed over the lamps to accomplish this.
After the cleaning, the printer conditions the drum to receive the next image by applying a uniform negative charge of -600v to its surface. The primary corona (in the toner cartridge) performs this function in some printers; in other models another charged drum does it. The primary corona is a thin wire; there are several corona wires involved in the print process. The primary corona must emit a charge of -6000v in order to apply a -600v charge to the drum. That is some seriously high voltage!NoteThe negative charge applies evenly across the photosensitive drum because a varistor grid filters it. Varistor gets its name from the term variable resistor: It does not conduct electricity until a specific voltage level is achieved.
Now comes the important part: The data in the printer’s memory is written to the drum using a laser. Rather than writing it with ink or toner, however, it writes by shining a very precise laser on the photosensitive drum in certain spots, changing the electrical charge in those spots. As the drum cylinder rotates past the laser, it sweeps across the surface, turning on and off to neutralize certain areas to about -100v. These neutralized areas will be the spots where toner adheres to the drum later in the process and then transfers to the paper.
In the early laser printers, the on/off status of the laser could be changed 300 times per inch, and the drum rotated 1/300 of an inch with each horizontal sweep of the laser, resulting in a 300 dots per inch (dpi) maximum resolution. Today’s laser printers can achieve 600 dpi or even 1200 dpi.
Step 4: Paper feed
Now it’s time for the paper to join in. Feed rollers draw the paper into the printer from the paper tray. Registration rollers hold the paper until it’s time for it to be released, making sure that the top of the paper feeds in exactly at the moment when the laser image of the page that’s on the drum rotates past it.
Step 5: Toner pickup
Steps 4 and 5 occur more or less simultaneously; as the paper is being drawn in, the toner is being applied to the drum.
The toner cartridge contains a rotating, magnetic, metal-developing cylinder, a toner reservoir, and a height control mechanism that limits the amount of toner the cylinder can pick up at a time. Toner consists of plastic resin particles (the particles that melt to produce the image on paper) and iron oxide (the particles that are affected by magnetic attraction and electrical charges). The toner’s metal particles adhere to the magnetic cylinder, and the cylinder presents the toner to the drum as it passes by. The developing cylinder is charged to -600v, like the blank portions of the photosensitive drum, and the toner adhering to the cylinder also takes on that same charge.
TipIf you ever get toner on fabric accidentally, you can get it off with a magnet, since the toner is about 50 percent iron oxide.
As the drum passes by the cylinder, the toner ignores all the areas charged to -600v because that’s the same charge as itself. It jumps off and clings to the areas with the lesser charge (-100v), however, and that’s what makes the toner stick to the drum.Step 6: Toner transfer to paper
At this point, the image exists on the drum, complete with toner. If you could look inside the printer as it operates (you can’t, by the way, because of the safety features in place) and stop the drum from rotating for a moment, you could see the page on the drum, just as it is to be printed.
As the paper feeds into the printer, the transfer corona applies a +600v (positive) charge to the paper. When the paper passes by the drum, the -100v charged toner on the drum jumps off onto the positively charged paper. Then, the paper runs past a static charge eliminator, which is a row of teeth with a negative charge that reduces the paper’s highly positive charge.
Step 7: Fusing the toner to the paper
The image is now on the paper, but it’s not secure there; it’s just loose toner held in place by gravity and a weak electrostatic charge. For permanent application, it must be fused. Fusing is basically melting the toner’s plastic particles so they stick, or fuse, to the fibers in the paper.
The fuser roller is a nonstick cylinder with a high-powered lamp inside it that heats the paper to around 330 to 355 degrees Fahrenheit. As the paper passes by it, the toner melts. A fabric or felt-cleaning pad, in constant contact with the fuser roller, helps keep it clean. With many laser printers, you change the cleaning pad whenever you change the toner cartridge.
If you have ever been warned not to use inkjet-type transparencies in a laser printer, the fuser is the reason. Any material that melts at less than 350 degrees is going to melt inside a laser printer, resulting in a huge mess and the need to replace the fuser roller assembly.
The final part of the fusing assembly is the pressure roller. It’s a rubber roller that presses against the fuser roller; the paper feeds between it and the fuser roller on its way through the printer. The fuser roller can leave an indent on the softer pressure roller because of the heat it produces, so the printer’s internal software will rotate the assembly periodically to keep this from happening.That’s how a laser printer works. Each printer has built-in sensors at critical points that check whether the paper is in the right place for that step to occur. The printer knows how long it should take for the paper to move from one sensor to the next, and if the paper is delayed, the printer gives you a paper jam message.
Troubleshooting problems with laser printers
Now that you are familiar with the printing process, you can probably guess some of the common problems and their causes even before I explain them. The best way to figure out the cause is by identifying at what point in the process the printer is breaking down.
Loose or smeared toner
Here’s an easy one. If the toner is loose (that is, not fused to the paper), the fuser is not melting the toner, and thus the toner is not fusing with the paper. Make sure the fuser is heating; if not, replace it.
Similarly, smeared toner happens because the nonstick coating on the fusing roller is scratched or has baked-on debris. You can try to clean it with a soft cloth and alcohol, but make sure you let it cool down first!
NoteIn this article, I recommend replacing certain parts, but unless you are a technician working for an authorized service center for that type of printer, you might not be able to get the needed parts easily.
Smeared output can also result when you refeed a printed page into the printer to make a double-sided page. This happens because the rubber rollers that grip the paper to pull it into the printer can pick up toner from the first side’s printing and smear it.Vertical white areas
To fix this problem, clean the corona wires. Why? This problem is caused by either the main corona or the transfer corona being covered with toner in a certain spot. A quick fix is to change the toner cartridge, even if it isn’t empty. Because the primary corona is located in the cartridge, this will correct problems with a dirty primary corona.
To clean corona wires, use a special felt-lined tool that comes with your printer or use an alcohol-dipped cotton swab. But be very careful! Corona wires are thin and easy to break with too much pressure. To locate the primary corona, remove the toner cartridge and look for an exposed wire. The transfer corona’s location depends on the printer, but it is usually protected with a webbing of filament threads. Not all laser printers allow you access to the transfer corona, so check your manual if you can’t find it.
Gray mist
If the white areas look like they have been lightly sprayed with a gray mist, making them look slightly dirty or dingy, the problem is also likely to be a dirty corona wire. (See the preceding section.)
This can also be the result of turning the printer’s print density control up too high. The newer the drum, the lower this setting can be. As the drum ages, you must turn up the print density control higher to achieve sharp black printouts. However, if you turn it up too high, the entire page acquires a dirty gray tinge. Some printers include the drum in the toner cartridge, so you get a new one each time you change toner. On other printers, the drum is separate, and you must eventually replace it when it wears out.
Printing not dark enough or varied in darkness
If the print is a dismal gray rather than a sharp black, you are probably almost out of toner. This can manifest itself evenly across the entire page or in splotches or stripes, depending on the printer.
Sometimes you can wring a little bit more out of a toner cartridge by taking it out and gently shaking it from side to side (never up and down, as toner can spill out). You can also try turning up the printer’s contrast adjustment, if it has such a knob (usually on the back side if it exists). Faded print can also result from a dirty corona wire, because a dirty wire inhibits a full electrical charge from being passed.
If the printouts are consistently varied in density, and you have to frequently remove the toner cartridge and shake it to redistribute the toner inside it, make sure the printer is sitting on an even, flat surface.
Horizontal black lines
A horizontal black line on the printout is probably the result of a dirty or damaged roller. There are lots of rollers in the printer, and you can use the space between the lines on the page to determine which roller is causing the problem. Measure the distance between the errant black lines on the page and then use Table A to determine which part might be causing the problem.
| Distance between lines | Faulty Part |
| 0.5” | Registration assembly |
| 1.5” | Upper registration roller |
| 1.75” | Lower registration roller |
| 2.0” | Toner cartridge developer roller |
| 2.56” | Lower fusing assembly roller |
| 3.16” | Upper fusing assembly roller |
| 3.75” | Toner cartridge photo drum |
Regularly spaced splotches
If there are evenly spaced black spots but they don’t extend all the way across the page, the problem is probably a scratch or flaw in the drum or a build-up of toner on the fusing roller. If the spots are less than three inches apart vertically, it’s probably the drum, because the drum has a larger diameter than the fusing roller.
Vertical black line on edge of page
This can indicate an almost empty or faulty toner cartridge or (less frequently) some spilled toner inside the printer.
All white page
If nothing appears on the page at all, you might be completely out of toner. However, most modern laser printers will inform you of this fact and not simply quit producing output. This problem can also be the result of a broken transfer corona. Remember, the transfer corona transfers the toner from the magnetic roller to the drum, so if that wire isn’t doing its job, you won’t get any toner on the page.
All black page
This usually means the primary corona is broken. The primary corona applies the -600v charge to the drum, and the toner also receives a -600v charge from the magnetic roller. If the drum isn’t charged enough, the toner will jump off onto the drum indiscriminately, resulting in a page full of black toner.
Summary
Now that you know how a laser printer works and a few simple fixes for common problems, you are well on your way to handling most troubleshooting issues. Also, by familiarizing yourself with these concepts, you are sure to have an easier time completing any laser printer question that might pop up on the A+ exam. Look for my follow-up Daily Drill Down to fill you in on other common areas of laser printer confusion: Postscript, interfaces, fonts, and driver settings.
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FAQs
What are the parts of a laser printer inside? ›
The key parts of the printer include, toner cartridges, image drum (also known as drum unit or photo-conductor), transfer roller or belt, fuser unit, laser, and mirrors.
How does a laser printer work step by step? ›Like a photocopier, laser printers read the electronic data from your computer and beam this information onto a drum inside the printer, which builds up a pattern of static electricity. This attracts a dry powder called toner onto the paper which is then fused using heated rollers.
What is the common problem of laser printer? ›Paper Jams
This is a common laser printer problem. Primary causes include grime, dust, worn rollers, or incorrect paper weight. The most basic way to prevent paper jams is simply through regular cleaning of your printer. Also, replace parts as needed.
The order of the imaging process in a laser printer is processing, charging, exposing, developing, transferring, and fusing.
How does a printer work step by step? ›The printer's laser projects your print onto a drum. A drum then uses static electricity to attract the dry toner to the drum's cylinder. The drum then rolls the toner onto the paper to create your print. The toner powder is melted and pressed onto the paper with heat from the fuser as it goes through a set of rollers.
How does a laser system work? ›A laser is created when electrons in the atoms in optical materials like glass, crystal, or gas absorb the energy from an electrical current or a light. That extra energy “excites” the electrons enough to move from a lower-energy orbit to a higher-energy orbit around the atom's nucleus.
What are three common faults that occur with a printer? ›- Paper Jams. Paper jams are perhaps the most loathsome of all printer problems. ...
- Poor Print Quality. When it comes to smudges, faded type and poor image quality, there are a couple of issues that could be going on. ...
- Nothing is Printing. ...
- WiFi Printing Takes too Long.
Common factors include driver problems, software issues, hardware failures and overuse.
What are 4 components of a laser? ›There are 4 main elements that are required to start the generation of light and make your own laser; the gain medium, the pumping energy, cavity reflections and the output coupler: The gain medium: To make your own laser, you need a source of light at the required wavelength known as the gain medium.
What are the six major types of printing processes? ›- Offset Printing.
- Lithography.
- Digital Printing.
- Gravure.
- Screen Printing.
- Flexography.
What are the three basic steps in printing? ›
Each printing process is divided into prepress, press, and postpress steps. Prepress operations encompass steps during which the idea for a printed image is converted into an image carrier such as a plate, cylinder, or screen.
What type of device is a printer internal? ›A printer is known as a peripheral device.
What part of the printer is the printhead? ›The printhead is a component in a printer that houses ink cartridges. It's typically located under the cover of your printer, and it can become clogged with ink over time.
What is the most important part of a printer? ›Connectors
The connectors are the most essential amongst all the parts, as it the only medium that lets the power supply in, and the only medium to send the computer's printing commands in to the printer as well.
The Engine Controller board contains the main controller logic, power supply, laser, and fuser control and coordinates all print engine activities.
What two components are most likely to be replaced in a laser printer? ›The main consumables of this process are the toner and the drum. The toner for laser printers is contained in a replaceable cartridge, avoiding the need to decant this very fine powder from one container to another.
What is laser printer with diagram? ›A laser printer is a popular type of computer printer that uses a non-impact photocopier technology where there are no keys striking the paper. When a document is sent to the printer, a laser beam "draws" the document on a selenium-coated drum using electrical charges.
How do laser printers install and work? ›- Step 1: select language and country. If you switch on the printer, it automatically starts to initialize. ...
- Step 2: choose a connection method. ...
- Step 3: download the required software. ...
- Step 4: select the paper tray.
The most widely used print processes are surface, flexographic (flexo), gravure and screen. It is important to recognize that each process is capable of yielding attractive, stylized and salable products.
What are the basic functions of a printer? ›For Scanning and Copying
The all-in-one printers are commonly used for offices or homes usually have 3 main functions, print, scan, and copy. The scan function is used more at the offices than at home. With this technology, we can store our documents in a digital form.
What is printer explain its working? ›
A printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard-size, 8.5" by 11" sheets of paper. Printers vary in size, speed, sophistication and cost.
What are the features of laser printer? ›Common features for laser printers include color printing, copying and or sorting capabilities, industrial metal housing, user controls, indicators, application software, and cutters. Laser printers with color printing are capable of color output in addition to monochrome output.
What are the three processes of laser action? ›We may conclude that, laser action is preceded by three processes, namely, absorption, spontaneous emission and stimulated emission - absorption of energy to populate upper levels, spontaneous emission to produce the initial photons for stimulation and finally, stimulated emission for generation of coherent output or ...
What are the basics of laser? ›A laser consists of two fundamental elements: an amplifying or gain medium (this can be a solid, a liquid or a gas). This medium is composed of atoms, molecules, ions or electrons whose energy levels are used to increase the power of a light wave during its propagation.
What are the 5 steps in production of laser? ›- Excitation by pumping light.
- Fluorescence and start of stimulated emission.
- Growth of stimulated emission along the axis of medium.
- Continued amplification by stimulated emission and output from laser.
- Check to make sure the printer is turned on and connected to the same Wi-Fi network as your device. ...
- Unplug and restart your printer. ...
- Set your printer as the default printer. ...
- Clear the print queue. ...
- Reset the service that manages the printing queue.
- Turn off the printer, turn it back on. As simple as it seems, this is one of the most effective ways to get a printer back on track and functioning normally.
- Turn off the computer, turn it back on. ...
- Check the connections. ...
- Check the status. ...
- Check the print queue. ...
- Invest in a new printer.
- Blank pages. The sealing tape or tab may not have been removed from your toner cartridge. ...
- Black pages. ...
- Thin, dark, vertical black lines. ...
- Skewed image/ jamming. ...
- Faulty registration/jamming. ...
- Light or faded print. ...
- Horizontal lines or repetitive defect. ...
- Background scatter.
- Open the HP Smart app, and then open Diagnose & Fix. ...
- Click Start. ...
- Follow any instructions provided if any issues are found.
- If the issue is not resolved, select one of the additional resources, or go to HP Customer Support and search for the specific issue or error message you are experiencing.
- Check if the printer is plugged in and turned on (though it may sound obvious). ...
- Reboot your computer and the printing device;
- Make sure you have access to the printer. ...
- Check your printer status. ...
- Verify that your printer is not in "Use Printer Offline" mode. ...
- Try printing a test page.
What is printer spooler? ›
The Print Spooler is software built into the Windows operating system that temporarily stores print jobs in the computer's memory until the printer is ready to print them. In some circumstances you may need to stop and/or restart the service. To access the Print Spooler you must open the Local Services console.
During what step in the troubleshooting process? ›- Identify the problem.
- Establish a theory of probable cause.
- Test the theory to determine the cause.
- Establish a plan of action to resolve the problem and implement the solution.
- Verify full system functionality and, if applicable, implement preventive measures.
The average lifespan of a printer is around 3-5 years. With proper upkeep and maintenance, some printers can last longer, but eventually your machine will need an upgrade.
How can I check if my printer is working properly? ›- In the Search box on the taskbar, type Devices and Printers.
- Touch or click Devices and Printers (Control panel).
- Touch and hold or right-click your printer.
- Touch or click Printer Properties. ...
- Under the General tab, Touch or click Print Test Page.
There are three fundamental parts in a conventional laser. An excitation mechanism, an active medium or lasing medium, and an optical resonator.
What are the components parts of a laser level? ›Parts of an Automatic Laser Level. The basic setup of an automatic level consists of the telescope, the circular level, three leveling screws, and a compensator.
What are the 7 steps of printing? ›...
The Seven Laser Printing Steps
- Step 1: Sending. ...
- Step 2: Cleaning. ...
- Step 3: Conditioning. ...
- Step 4: Exposing. ...
- Step 5: Developing. ...
- Step 6: Transferring. ...
- Step 7: Fusing.
Examples of print sources are books, magazines, scholarly journals, and newspapers.
How does printing work step by step? ›The printer's laser projects your print onto a drum. A drum then uses static electricity to attract the dry toner to the drum's cylinder. The drum then rolls the toner onto the paper to create your print. The toner powder is melted and pressed onto the paper with heat from the fuser as it goes through a set of rollers.
What is the most common printing process? ›Offset printing is still the most commonly used method of printing and is often called offset lithography.
What are three replaceable parts in a laser printer? ›
...
Maintenance kits include key components that should be replaced and typically include the following items:
- Pickup rollers and separator pads.
- Transfer rollers.
- Fuser assemblies.
- Toner.
Toner. A toner cartridge contains coloured or carbon / iron oxide powder (toner) that is positively charged, which is then melted onto the paper. The toner powder is distributed onto the paper evenly with the help of the doctor blade, forming the image that the drum has helped constructed.
What are the replaceable parts in a laser printer? ›- Fuser Assembly. The fuser assembly consists of a pair of plastic rollers. ...
- Transfer Roller. ...
- Pickup Rollers. ...
- Separation Pads. ...
- Corona Assembly. ...
- Fan Assembly.
- Switch your printer off, unplug and allow to cool down. ...
- Put on your latex gloves and dust mask. ...
- Remove the imaging drum. ...
- Remove the toner cartridge. ...
- Speak to a qualified engineer to clean internal parts. ...
- Clean surfaces with isopropyl alcohol wipes. ...
- Reassemble parts.
Separate drum units last quite a bit longer than a toner cartridge and typically should be replaced after the use of 3-4 toners. Your printer should inform you when it's time to replace the drum, but you can usually tell your drum is on it's last legs if you start to see black spots or lines across the page.
What part in a laser printer controls the data processing? ›The DC Controller is a small, printed circuit-board assembly that controls the timing of all the assemblies within the printer. All the sensors in the machine report data to it.
Is a laser printer input or output? ›Laser printers are output devices usually found in businesses and organisations. Using static electricity, the way they work is completely different to inkjet printers. Laser printers are ideal for high volume printing because they produce very high quality documents at fast speeds.
What does a fuser do in a printer? ›Definition of FUSER UNIT:
A component found in electrostatic printers, laser printers, and xerographic printers and photocopiers. The fuser unit is used to permanently bond toner to a substrate by applying heat and pressure. A fuser unit is made up of two rollers; one to apply heat and one to apply pressure.
...
How can I fix my laser printer's streaking issue?
- Remove the cartridge and rock it back and forth a few times over a trashcan to evenly redistribute the toner powder. ...
- Reinstall the toner cartridge and run a test print.
A maintenance kit is a set of replacement parts for a printer. Each printer has a preset maintenance interval, which occurs after a certain amount of pages are printed. The maintenance interval lets the user know that it's time to install the maintenance kit so that the parts within the printer do not get overused.
Can a laser printer get clogged? ›
Unlike inkjet printers, laser print heads don't get clogged with dried ink. However, dust and bits of debris can accumulate on a laser print-head lens, causing many of the same print-quality issues as a clogged print head on an inkjet printer, including blurred or faint text and images.
Can a laser printer drum be cleaned? ›Use an activated toner cloth, stretched tautly, and carefully wipe down the drum exterior to remove loose toner. Then use a cotton ball saturated with 99% pure isopropyl (rubbing) alcohol. Clean any patches of stubborn toner still attached to the drum. Use toner cloth or lint-free microfiber to clean the print rollers.
Do laser printer heads dry out? ›Laser printers use toner which will not dry out the same way an ink cartridge does. Unlike ink, which is liquid-based, toner is a dry powder composed of plastic components so it will not dry out. You can leave a toner cartridge in your printer for weeks untouched and it should still print.