The following are the 6 steps in the ElectroPhotographic (EP) print process of Laser Printer:
Cleaning: Cleaning the photosensitive drum includes residual toner left on the drum and removing the electrical charges left out on the drum. The physical cleaning is done with a rubber blade and the electrical charge cleaning is done with erasure lamps.
Charging: The next step in printing, is to charge the photo sensitive drum with high negative charge, this is done with the help of a corona wire.
Writing: A laser (type 3) sweeps the entire length of the drum, creating the static image of the matter to be printed. The places where the laser travel, the highly charges are neutralized. Other places of the drum, it remains highly negatively charged.
Developing: Now drum gets in close proximity to the toner. Because the toner is negatively charged, it gets attracted to the areas where the drum is neutral. It will not be attracted to the places where the drum is highly negatively charged. Thus the image of the page to be printed formed on the photosensitive drum.
Transferring: Now, the toner on the drum gets attracted toward the paper, by using highly positive charges developed on the surface of the paper. The "transfer corona" is used to generate highly positive charge on the paper surface and to attract the toner from the drum. Thus the image of the page to be printed formed on the paper. But still, the toner is loose and can get easily smeared.
Fusing: In order to permanently bond the toner particles to the paper, the paper is passed through rollers. One of the rollers, the non stick roller is heated by a high intensity lamp, generating the heat necessary to bond the toner to the surface of the paper.
Problems associated with laser printers and probable causes:
Speckled pages: The causes for this may be
The failure to clean the drum after printing properly, or
The drum might have developed scratches.
Blank pages: The causes for white pages may be, A. The toner would have dried out, replace the toner. B. The transfer corona, that is responsible for transferring the toner to the drum might have failed. C. The High Voltage Power Supply (HVPS) failure will also result in white pages.
Ghosted Images: Ghosting occurs when previously printed pages are printed again, though much lighter than the present image. The most likely cause is that the erasure lamp might not be working properly, thus leaving some charges representing the earlier image left on the photosensitive drum before new image is written. Also check the cleaning blade, which is responsible for scaping the residual toner.
Smudged images: If the fusing fails, the toner will not bond with the paper. Check the halogen lamp responsible for heating.
Impact printers are capable of printing multipart forms, since they can give necessary impact to print to multiple forms simultaneously.
ECP (Extended Capability Port) has less control overhead and best suited for transferring large chunks of data, such as between the computer and laser printer.
InkJet Printers is the generic name given for contactless printing using ink. Friction feed is most commonly used with laser printers, and Inkjet printers.
Printer parallel ports come in the following varieties:
Unidirectional: Here, the data travels only from the computer to the peripheral (printer) device.
Bi-directional: Here, the data travels both from the computer to the peripheral device and vice-versa.
ECP (Extended Capability Port): ECP mode offers bi-directional data transfer, as well as DMA for data transfer.
EPP (Enhanced Parallel Port): In addition to bi-directional features, it offers an extended control code set
The port that a printer is using can be found by going to Control Panel -> Printers and right click on appropriate printer. Choose Ports tab to view the port (like COM1, COM2, USB001, etc.) that the printer is using.
Serial cable maximum length is 50 feet.
Parallel cable maximum length is 10 feet.
Longer cable lengths may lead to some errors & garbage characters.
RJ – cables:
RJ-11: These connectors are used to link modem / phone to the phone line. They have only two pins that get into the modem
RJ-14: RJ-14 connectors are dual-line phone jacks that can accommodate up to 2 telephone line.
RJ-45: RJ-45 cable is widely used for attaching UTP cable in LAN environment. These connectors have eight pins.
The widely used interface cables have the following pin count:
SCSI Ultra wide-68 pin
Ultra IDE cable has 80 wires, and handles better speeds compared to IDE cable with 40 wires. The additional wires are introduced to reduce noise and thereby improving speed
Thin co-axial and thick co-axial cables have conductive grounding sheath surrounding the center conductor. Therefore, the electromagnetic interference (EMI) is significantly less.
Cat 6 cabling is recommended for Gigabit Ethernet networking.
Centronics cable, used for parallel printing will have a male DB-25 connector at one end and a female 36 pin connector at the other end.
When communicating across a serial cable, the most probable cause that the screen is dumping garbled characters is that the communication settings are not correct. Check the speed, parity, start/stop bits etc. If this is all correct, then you need to check the cable. Check whether you need a straight / cross cable, and the pin connections.
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