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Inhibits the flow of electricity
Material that permits the flow of electricity
Conductive Materials
  • Metals
  • Some plastics
  • Some liquids

Insulatory Materials
  • Ceramics
  • Plastics
  • Gases
Voltage- V
  • Analogous to water pressure.
  • Measured in volts
  • Also called the potential or potential difference.
Voltage by Country
  • America 110V
  • Japan 110V
  • Europe and most other countries 220-240V
Computer Voltage
5 or 10V for components
A measure of the flow of electrons past a certain point. Essentially measures the speed of electrons through the conductor. Measured in Amps or Ampheres.
A path from the source
Complete Circuit
A closed circuit from the source through any intervening devices and back to the ground.
Open Circuit
Aka an incomplete circuit. An interrupted flow of a current. The principle behind the switch.
Direct Current. Current that flows in a single direction at a constant voltage through the circuit. Batteries (most electronics components like circuit boards, chips, and internal devices.)
Alternating current. Current flows repeatedly back and forth through the circuit at a constantly varying voltage. (Building's electrical system, most household devices) AC Systems complete a full cycle. Voltage change from zero, through maximum voltage, and back to zero many times per second. US and Canada 60 Cycles per second.  Europe 50 hz (hertz) AC electricity.
Direct Current. Force that opposes the flow of DC through a conductor.
AC. Force that opposes AC flow through a conductor.
Heat/ Energy
When resistance or impedance are present electrical energy is converted to heat or some other form of energy. All conductors possess either resistance or impedance.
Measure of resistance and impedance. One ohm is defined as the resistance of a system in which 1V maintains a current of 1 amp.
Electrical Power
Measured in Watts (W). A derived quantity of Voltage times Current. It measures the energy delivered by the flow of electricity. A power supply rated 450W delivers 450 watts of power although actual may vary.
Electrical Energy
Electrical Power delivered over time. 1kWh (kilowatt hour) is the flow of one kilowatt (1000W) delivered for a one hour period.
  • V
  • Force of electricity (water pressure) caused by a difference in charge.
  • Current
  • mA - millamp
  • 1mA= 1/1000 amp
  • Hz
  • Cycles per second of AC.
  • 60 cycles per second = 60 Hz
  • Ω
  • Resistance and Impedance
  • W
  • derived from V * current
Kilo-watt hour
  • kWh
  • watts of power per hour
  • 1000 watts per hour = 1kWh
Technician Concerns
  • Power supplies with a higher power rating can supply more power to more components and peripherals than power supplies with lower ratings can.
  • As a tech I will work with volts when connecting components to a PC.
  • I will encounter watts as a power supply rating.
  • The purpose of a power supply is to convert the 1--V AC electricity delivered at the outlet to the 5V and 12V DC electricity required by the computer's components.
What kills you?
  • Current not Voltage
  • 1-10-100 rule states that you can feel 1mA of current through your body, 10mA can cause muscle contractions where you can't release a power source, 100 mA can stop your heart.
Calculating Current
  • Voltage, current, and resistance are related through this formula v=i*r.
  • Voltage=current in amps*resistance
  • At a given voltage current increases as resistance drops. A dangerous level of current can be reached if resistance is reduced sufficiently.
Human body and electricity
  • Resistance of about 500,000Ω.
  • Moisture and sweat lower resistance to around 5000Ω on a small area of skin.
  • Contact with a greater area of skin reduces resistance even further.
  • Immersion of a hand or foot or direct blood contact can reduce resistance down to 100Ω.
Electrostatic Discharge
  • ESD
  • Occurs to balance the difference in charge of two objects.
Name six ways to prevent static buildup.
  1. Don't shuffle your feet as you walk.
  2. Increase the humidity in the room or building.
  3. Keep yourself grounded as you work and move. Use the ESD toolkit.
  4. Wear cotton clothing.
  5. Remove carpeting from computer service rooms and computer rooms.
  6. Use an air ionization system.
Name six ESD Safety Precautions.
  • Do not touch exposed electrical contacts with any part of skin.
  • Touch only insulated handles of tools, probes, etc.
  • Leave covers on equipment unless you need to access their internal components.
  • Work one-handed.
  • Remove jewelry
  • Keep hands and work areas clean and dry.
Static Dangers
  • Static is not dangerous to humans but can be potentially dangerous to electronics.
  • A static spark could melt components or alter data.
Discharge Voltages
  • To feel a static shock you must experience a discharge of 3000V.
  • 8000V will generate a visible spark.
  • Walking across carpet on a dry day can generate up to 35000V.
  • 1000V can damage electronics.
Preventing Discharge
  • Equalize the charge safely. Unplug the equipment and touch the metal part of its chasis.
  • If you must move around as you work, keep yourself grounded (anti-static wrist strap) so that charges can't build up.
  • Do not leave the computer plugged in while servicing.
Opening the Case
  • Pay attention. Older cases are closed by screws and newer cases latch.
  • Open the side where the connectors extend through the back of the computer.
ESD Precautions for opening the computer case (5 steps)
  1. disconnect the power cord from pc.
  2. Disconnect any other external cables.
  3. Release the restraining mechanisms (screws, slides, pushbuttons) that secure the side that exposes the internal components. If you open the wrong side close it before opening the other.
  4. Touch the metal frame of the computer and count to three to discharge static.
  5. Remove the front cover.
DC Power Supply
  • Converts AC to various DC voltages
  • Fan to cool supply, sometimes other components
  • Typically provide power conditioning functions, can maintain DC supplies during very brief drops in or outages of voltage.
Power Supply Voltage
Can work off of 110 or 220 V. Adjustable by switch.
Power Supply Watts
  • Modern supplies offer 300 Watts or more. Older offer 200 W or less.
  • The supply can only draw enough power to supply internal components and nothing more.
Motherboard Power Requirement
  • 30W excluding chip and memory. (Sleeping uses less)
Memory Power Requirement
  • 10W per 2GB chip
CPU Chip Power Requirement
  • AMD Phenom 65-140W
  • AMD Athalon 64, 45-125W
  • Single and Dual Core Itanium 100W
  • Pentium 4 and Athalon 65W
  • Older CPU's use 50W or less
Hard Drive Power Requirement
Optical Drive Power Requirement
  • New CD/DVD drives 5-15W
  • Older 10-20W
Floppy Drive Power Requirement
Adapter Card Power Requirement
5-30W. High end graphics cards require more than standard.
Power Supply Outputs
Most power supplies provide 3 voltage output levels at various amperage rating to supply power to the internal components.
Power Supply
  • +3.3 V Output
  • 14 A
  • AGP video cards
  • Motherboard
Power Supply
  • -5V Output
  • 0.3 A
  • ISA bus (AT bus) adapter cards
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