Electricity and power supplies

1
Electricity and power supplies

• Unit objectives
• Identify electrostatic discharge, and follow ESD
  safe practices while working with computer
  components
• Install a new power supply in a PC
• Troubleshoot faulty power supplies

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Topic A

• Topic A Electrical safety
• Topic B Power supplies
• Topic C Power supply troubleshooting

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Characteristics of electricity

• Electricity Flow of electrons
• Conductor Permits flow of electricity
• Insulator Inhibits flow of electricity
• Voltage Force of electricity caused by
  difference in charge at two locations
• Measured in volts
• Also called potential or potential difference
• Officially designated as uppercase V
• May see it as lowercase v

continued
4
Characteristics, continued

• Current Measure of the flow of electrons past a
  given point
• Measured in amps, or amperes
• Must be a complete circuit (closed circuit)
• Direct current Flows in one direction, at
  constant voltage, through circuit
• Alternating current Flows repeatedly back and
  forth through the circuit, at constantly varying
  voltage levels

continued
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Characteristics, continued

• Resistance Force that opposes the flow of DC
  through a conductor
• Measured in ohms (O)
• Impedance Like resistance, but applies to AC
• Power
• Measured in watts
• Calculate by multiplying voltage by current
• Energy Electrical power delivered over time

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Activity A-1
Examining the characteristics of electricity
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Electricity

• Current can kill
• The 110100 rule
• Calculating current
• V i r
• Resistance of the human body is about 500 KO
  (500,000 O)

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Safety precautions

• Dont touch exposed contacts
• Touch only insulated handles of tools
• Leave covers on equipment
• Work one-handed
• Dont insert anything into wall outlets
• Remove jewelry, watches, etc.
• Keep hands clean and dry
• Dont work in wet surroundings

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Activity A-2
Considering electrical safety
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Electrostatic discharge (ESD)

• Buildup of charges
• Static dangers
• Discharge voltages
• 3000 volts to feel
• 8000 volts to see spark
• 35,000 volts on a dry day on carpet
• 1000 volts can damage electronics

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Preventing static buildup

• Dont shuffle your feet
• Increase the humidity
• Keep yourself grounded
• Wear cotton, not synthetics
• Remove carpeting
• Use air ionization system

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Preventing static discharge

• Equalize charge differences safely
• Unplug the equipment
• Touch the metal chassis or power supply
• Keep yourself and equipment connected
• Wrist straps and antistatic mats
• Static-safe bags
• Goal is to be at a charge potential thats equal
  with the device youre servicing (not with
  ground)

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Antistatic (ESD) wrist straps
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Typical internal components
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Slide catches
Slide catch, move to open side of case
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Determining which side to open
Open this side to access components
Ports and connectors attached to motherboard
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Removable front cover
Alignment posts
Alignment holes
Spring catches
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Activity A-3
Opening the computer case while following proper
ESD precautions
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Topic B

• Topic A Electrical safety
• Topic B Power supplies
• Topic C Power supply troubleshooting

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PC power supply

• Converts wall voltage to DC voltages for PC
  components
• Includes a fan
• Provides some conditioning functions
• Can maintain power during brief drops and outages

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Power supply specifications

• Rated by DC power output in watts
• Modern systems typically gt300 watts
• Older systems lt200 watts
• Rating isnt an indicator of power draw
• Draws only the power needed to supply internal
  components

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Typical power requirements
Motherboard 30 W
Memory 10 W per 2 GB
CPU 45145 W or more
Hard drive 515 W
CD-ROM drive 520 W
Floppy drive 510 W
Adapter card 530 W
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Standard outputs
3.3 V 14 A AGP video cards, motherboard
-5 V 0.3 A ISA bus adapter cards
5 V 30 A Motherboard, CD/DVD drives, hard drives, PCI adapter cards, Pentium III and earlier processors
5 V 0.85 A Soft power switch
-12 V 1 A Older network adapters and serial ports
12 V 12 A CD/DVD drives, hard drives, Pentium 4 and Athlon processors, motherboard
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Power connectors

• Two standards
• Drive power connectors
• Motherboard power connectors

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Peripheral power connector

• Molex connector
• Typically used to connect hard drives and optical
  drives

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Floppy power connector

• Berg connector
• Smaller than Molex
• Typically used to connect floppy drives

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SATA power connector

• New, for Serial ATA drives

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Wire colors

• Yellow 12 V
• Red 5 V
• Black ground

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Motherboard power connectors
Single power connector
Dual power connectors
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20-pin ATX v1.0
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24-pin ATX v2.0
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Power supply form factors

• Describes size and shape
• Must fit
• Case
• Motherboard
• Other components
• http//en.wikipedia.org/wiki/?Motherboard_form_fa
  ctor

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Activity B-1
Identifying your computers power supply
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Installing a power supply

1. Shut down computer
2. Unplug computer
3. Remove cover from computer
4. Disconnect all power wires from components,
   including motherboard
5. Remove retaining screws
6. Remove power supply
7. Install new power supply and screw it into place
8. Connect power wires to components as needed,
   including motherboard
9. Replace cover
10. Plug computer into outlet, and boot system to
    test your work

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Selecting the voltage

• Set power supply to run on 110 V or 220 V
• With computer off, slide switch
• Usually located near power cord port

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Activity B-2
Installing a new power supply
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Topic C

• Topic A Electrical safety
• Topic B Power supplies
• Topic C Power supply troubleshooting

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An AC signal
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Power problems

• Blackout Total loss of power
• Brownout Brief decrease in voltage level
• Noise Disruption of smoothly varying AC signal
• Spike Very brief increase in voltage
• Surge Brief increase in voltage (longer than
  spike)

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Power conditioning

• Surge protectors
• Filter out spikes and surges
• Battery backup devices
• Condition the power signal
• Some protect against brownouts
• Continuous UPS vs. standby UPS
• UPS monitoring and management software
• Generators
• Provide power for extended periods
• Use a variety of fuels
• Computer-grade generators produce clean,
  consistent AC signals

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Activity A-4
Discussing power conditioning equipment
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Electrical measurements

• Measure electrical values with a multimeter
• Multimeters can be digital or analog
• Use to measure
• Resistance
• Voltage
• Current
• Continuity

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Measuring resistance

1. Turn off the device youre measuring and
   disconnect it from its power source
2. You might need to disconnect the device from its
   circuit
3. Set the multimeter to read resistance
4. Touch the two leads of the multimeter together
5. Touch the black and red probes to either side of
   the circuit to be measured
6. Read the resistance from the meters display

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Measuring voltage

• Verify the power supply is on
• Set your multimeter to read either DC or AC
  voltage
• Touch the black probe to the ground, and touch
  the red probe to the spot where you want to
  measure the voltage
• Read the voltage from the meters display
• You must exercise care when taking voltage
  readings as the computer is powered up

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Measuring current

• Break the circuit and insert the meter in the
  break
• Ammeter doesnt require break
• Clamp ammeters are often used to measure current
  flow in 110 V and higher circuits

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Measuring continuity

• Set your multimeter to display resistance (ohms)
  and look for circuits with zero resistance
• Also can use continuity mode, if available

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Activity C-2
Measuring electrical values
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Power supply problems

• Computer fails to boot when powered on, but boots
  after CtrlAltDel
• Computer intermittently stops working or reboots
• You dont have enough power connectors for all
  the devices you want to install
• Computer fails to boot at all (no lights or
  beeps) fans dont start
• Computer fails to boot, but fans start

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The Power_Good signal

• Signals CPU that power is stable and sufficient
• 5 V over specific wire
• Must arrive at correct time

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Activity C-3
Troubleshooting power supply problems
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Unit summary

• Identified electrostatic discharge, and followed
  ESD safe practices while working with computer
  components
• Installed a new power supply in a PC
• Identified and resolved issues with faulty power
  supplies