Printers TechNotes - Laser Printers

Laser printers use an electro-photographic process to print one page at a time using a plastic powder (toner) instead of ink.
Laser printers are nonimpact devices, hence they make less noise compared to dot matrix printers and generally faster than dot matrix or inkjet printers.

Print resolution is measured in DPI (dots per inch) which ranges from 300 to 1200 DPI. Many modern laser printers are able to use a technology called Resolution Enhancement Technology to increase the maximum effective resolution to even more. Be aware that the higher the resolution or RET settings the higher the amount of physical RAM the printer will need.

Laser printer output is controlled by page description languages (PDLs: the Printer Control Language or PostScript.)

How does a laser printer work?
1. Photosensitive drum is cleaned (by an Erase lamp, and scraper)
2. Photosensitive drum is negatively charged (by the Primary Corona)
3. Image is written on the drum by positively charging the places where the toner should be placed (by Laser)
4. Toner with a negative charge is placed on the drum.
5. Toner is transferred to the paper. (The Transfer Corona positively charged the paper.)
6. The toner is melted onto the paper by the fuser (a heat and a pressure roll.)

Font Cartridges
Font Cartridges provide fonts on ROM boards and can be placed in many laser printers. Fonts can often also be 'downloaded' to RAM.

Troubleshooting Laser Printers
Symptom/Problem Possible cause(s) Possible solution(s)
Print results are too light, white/light columns. Toner is low.
Defective transfer corona. Replace toner cartridge / fill toner reservoir.
Ghosting Drum is not fully discharged, erase lamp not functioning, previous image used too much toner. 1. Print couple of black pages
2. Replace cartridge
3. Call a trained service technician to replace Erase lamp.
Memory overflow error Image size too large. 1. Reduce the print resolution and/or Resolution enhancements technology.
2. Add more RAM to the printer.
Prints totally black pages. Damaged primary corona Call a trained service technician to replace the primary corona.
Pages are dirty with toner. Dirty fuser.
Leaking cartridge.
Paper Transport component is dirty.
1. Print a couple of blank pages.
2. Clean/vacuum the printer.
Multiple pages are pulled in at a time. Wrong paper type.
Defective Paper transport. Try thicker paper and make sure it is clean/dry.

Miscellaneous notes:
- Do not connect a laser printer to an UPS, laser printers consume a lot of power so your UPS will be empty in no time.
- Always be careful when servicing a laser printer, you don't want your tie to get stuck in the fuser pulling you in... it's hot! ;)
- Some laser printer can be expanded with a duplexing paper tray that enables printing on both sides of pages.

INKJET PRINTERS

Characteristics of inkjet printers
Inkjet printers come in many different types and sizes they are mostly used as desktop printers and most of them are able to print in color.
Inkjet printers are generally cheaper to buy than laser printers, however they are more expensive to maintain. Cartridges need to be changed more frequently and special paper may be needed to produce a good quality image. Inkjet printers are non-impact devices hence are quieter than dot matrix printers.

Most inkjet printers work by spraying small ink onto paper through tiny nozzles. Spraying is initiated by heating the ink to create a bubble until the pressure forces it to burst and hit the paper. Then the nozzle gate is closed again and the process repeats. This occurs a thousands of times per second.

Most inkjet printers come with advanced tools that allow you to clean the nozzles (takes a lot of ink) and align new ink cartridges. Inkjet printers commonly provide a print resolution ranging from 300 to 1200 DPI.


Troubleshooting Inkjet Printers
Symptom/Problem Possible cause(s) Possible solution(s)
Print results are too light. Ink level in cartridge too low. Replace ink cartridge.
Print results are smudged. Paper not fit for inkjet ink. Try using other paper.
Printer does not print. 1. Printer is offline.
2. Printer is out of paper.

1. Turn printer online.
2. Add paper.
Paper gets stuck or does not advance. Damaged paper feed mechanism or just wrong type of paper. 1. Try using other paper.

DOT MATRIX PRINTERS

Characteristics of dot matrix printers
Although the inkjet printer replaced most dot matrix printers many companies still own a couple of them to print (mostly characters) on continues forms. Dot matrix printers are impact printers, they create images by striking an inked ribbon onto an paper using pins and make more noise than laser and inkjet printers. The pins are placed on the print head mostly in an array of 9 or 24 pins. Needless to say, the resolution is measured in dots per inch, the higher the amount of pins the higher the resolution. Paper is mostly feeded using tractor wheels although some dot matrix printers use a plain sheet feeder.

Print speeds, specified in characters per second (cps), varies from about 50 to over 500cps.

Troubleshooting Dot Matrix Printers
Symptom/Problem Possible cause(s) Possible solution(s)
Print results are too light. Ribbon cartridge is out of ink. (dry) Replace ink ribbon.
Error-led flashes. Printer overload. Leave it for a while and remove all print jobs. Try printing in smaller portions.
Printer does not print. 1. Printer is offline.
2. Printer is out of paper.
3. Printer is not connected.

1. Turn printer online.
2. Add paper.
3. Check cable connections.
Paper does not advance. Paper is not properly placed or paper-feed mechanism is broken. Make sure the paper is aligned and the tractor wheels are in place.
Characters are incomplete. Pins are stuck or broken.

Replace the print head

PRINTER CONNECTIONS

Parallel (LPT, IEEE 1284)
This is the most common used connection today.
-EPP / ECP
In the CMOS you are able to configure a parallel port to use EPP or ECP. Enhanced Parallel Port and Extended Parallel Port are both bi-directional standards, operate in 8-bit, and allow data transfer speed of approximately 2 MB/s. Some of the main differences are that ECP supports Direct Memory Access (DMA) and data compression, which enables higher transfer rates.
Serial
Some older printers can be connected to a Serial port (COM port).
USB
Many modern printers (especially desktop printers) use an USB connection. USB printers often can be connected and installed without having to reboot.
Infrared
Often used in combination with portable computers.
Network
Most printers in offices are network printers. These are attached to a Print Server (or a module simulating one) and are available to anyone with appropriate permissions in the network.

Current Printer related exam objectives for the 2002 A+ Core exam:
4.4 Identify the purpose of CMOS (Complementary Metal-Oxide Semiconductor), what it contains and how to change its basic parameters.
Example Basic CMOS Settings:
- Printer parallel port—Uni., bi-directional, disable/enable, ECP, EPP

Domain 5.0 Printers
This domain requires knowledge of basic types of printers, basic concepts, and printer components, how they work, how they print onto a page, paper path, care and service techniques, and common problems.

5.1 Identify basic concepts, printer operations and printer components.

Content may include the following:
Paper feeder mechanisms

Types of Printers
- Laser
- Inkjet
- Dot Matrix

Types of printer connections and configurations
- Parallel
- Network
- USB
- Infrared
- Serial

5.2 Identify care and service techniques and common problems with primary printer types.

Content may include the following:
- Feed and output
- Errors (printed or displayed)
- Paper jam
- Print quality
- Safety precautions
- Preventive maintenance