A Guide to PC Hardware Maintenance and Repair

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Chapter 17 Printing Technologies Getting it
All on Paper
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Objectives

• To take a look at the different types of printers
  on the market
• To see how some of the more common printers work
• Take a detailed tour of the laser printing
  process
• Learn a bit about troubleshooting and maintaining
  printers

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The Types of Printers

• Impact
• Inkjet
• Optical

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Impact Printers

• Line Printers
• Dot Matrix Printers
• Daisy Wheel Printers

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Line Printers

• Print a single line at a time
• More recent models assemble portions of entire
  pages before sending job to printer
• Are character based printers
• Can only handle the most rudimentary of graphics
• Very high speed

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Dot Matrix Printers

• Treat entire page as a single image
• Draw the page with a pattern of individual dots
• Can create more complex graphics than line
  printers, but no masterpieces will ever be
  created with one
• Useful for multi-part forms.

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Types of Dot Matrix

• 9-pin
• 18-pin (now obsolete)
• 24-pin
• 48-pin (now obsolete)

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9-pin Dot Matrix Print Head
24-pin Dot Matrix Print Head
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Trouble-shooting Dot Matrix

• An out of line platen produces type that looks
  like this.

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Trouble-shooting Dot Matrix

• An out of line print head produces type that
  looks like this.

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Trouble-shooting Dot Matrix

• Platens need to be kept clean
• Paper dust and debris must be frequently cleaned
  from tractor mechanism
• Print head need constant cleaning

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Daisy Wheel Printers

• Now obsolete (thank goodness!)
• Delivered very high-quality text
• Very noisy
• Very slow
• Short life span

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The Daisy Wheel printer used a print head
consisting of a hammer that struck the selected
letter on a flower petal of type. To change
font, you had to change the type wheel.
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Inkjet Printers

• Thermal
• HP and similar printers
• Piezo-electric
• Epson and similar printers
• No real advantage to either one
• Except that my Epson prints on the back of CDs!

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Thermal Inkjet Printers

• Brings ink to just past the boiling point
• A bubble pops out of the print head onto the
  paper

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Piezo-electric printers

• A microscopic crystal is excited by an electrical
  current
• Current causes crystal to jump, throwing a drop
  of ink onto the paper

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Optical Printers

• Laser
• LED
• The print process is so similar between the two,
  that Ill only discuss laser

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The Parts of a Laser Printer

• Photosensitive drum
• Toner cartridge
• Pickup roller
• Registration roller
• Transfer roller
• Fuser assembly
• Output assembly

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The Laser Printing Process

• Cleaning
• Conditioning
• Writing
• Developing
• Transfer
• Fusing

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The Cleaning Process

• A strong light source neutralizes the charge on
  the imaging drum
• A cleaning blade scrapes off any residual toner
  from the previous job

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The Conditioning Process

• The charging roller applies a strong negative
  (-800 to -1200V) charge to the imaging drum
• On old model printers, this was done with a part
  called the primary corona.

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The Writing Process

• The laser print head sends a stream of light
  pulses toward the imaging drum
• A spinning helical mirror assures that the beam
  covers the entire printable surface
• Where ever the laser beam strikes the imaging
  drum, a virtual dot with a -200 to -400V charge
  is created

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Developing

• In the toner cartridge, a small amount of toner
  is transferred to the charging reservoir, where
  it is given a negative charge of around -600V
• Where the imaging drum is exposed the -600V toner
  sticks to the -400V dots,
• The -1200V unprinted areas repel toner
• There is now an upside-down reversed image on the
  drum.

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Transfer

• The transfer roller applied a positive charge to
  the paper
• The negatively charged toner is sucked off the
  imaging drum onto the paper, where electrostatic
  charge will hold it for a while

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Fusing

• A heated drum presses the paper against a
  pressure roller
• The heat melts the toner onto the paper

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Maintaining Laser Printers

• Pickup and separation rollers need to be changed
  when they get worn
• Loose toner gets into the cartridge cavity and
  must be cleaned out
• Fuser assemblies need to be replaced periodically
• Transfer rollers need to be replaced periodically

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Printer Languages

• Printer Control Language
• PCL-3 was first to support laser printers
• PCL-5 was the first to support complex graphics
• PCL-6 supports vector graphics, advanced features
  and color

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Printer Languages (cont.)

• Postscript
• Originally developed by Apple
• Capable of advanced graphics functions
• Generally perceived as superior to PCL for
  high-end printers

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Printer Languages (cont.)

• Windows GDI
• Only works in Windows
• Uses the computers resources for processing and
  memory
• Can be very inexpensive, but has strong impact on
  overall system performance

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IEEE-1284

• A standard to assure that all 1284-compatible
  devices work with one another
• To be IEEE-1284 a device or cable must support
  EACH one of several different standards, old and
  new

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IEEE-1284 Standards

• Compatibility Mode
• Also known as Centronics. Unidirectional signal.
  Around 150Kb/s data transfer
• Nibble Mode
• Sends 4-bits of data at a time
• Requires software support
• Bi-directional communications

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IEEE-1284 Standards (cont.)

• Byte Mode
• Bidirectional mode that sends 8 bits at a time
• Enhanced Parallel Port
• Allows different types of signals to be sent on
  each clock cycle
• Data transfer rates around 500Kb/s

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IEEE-1284 Standards (cont.)

• Extended Compatibility Port (ECP)
• Provides for both data and command cycles
• Allows multi-channel communication between
  devices
• Requires the use of a DMA channel