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Electricity and power systems

Unit objectives Measure and describe the

characteristics of electricity Identify static electricity and follow

ESD safe practices when working with computers

Describe the purpose and features of power supplies and install a new power supply into a PC

Troubleshoot faulty power supplies

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Topic A

Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting

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Electricity characteristics

Voltage Current Alternating or direct current Resistance and impedance Power and energy

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Activity A-1

Examining the characteristicsof electricity

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Electrical safety

Current can kill The 1–10–100 rule Calculating current

V = i * r Resistance of the human body

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Safety precautions

Don’t touch exposed contacts Touch only insulated handles of tools Leave covers on equipment Work one-handed Don’t stick things into electrical

sockets Remove jewelry, watches, etc. Keep hands clean and dry Don’t work in wet surroundings

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Activity A-2

Considering electrical safety

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Digital multimeter

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Analog multimeter

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Using a multimeter

Measuring resistance Measuring voltage Measuring current Measuring continuity

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Activity A-3

Measuring electrical values

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Topic B

Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting

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Static electricity

Build up of charges Static dangers Discharge voltages

– 3,000+ volts to feel– 8,000+ volts to see spark– 35,000 volts on a dry day on carpet– 1,000 volts can damage electronics

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Prevent static build-up

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

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Prevent static discharge

Equalize charge differences safely– Unplug the equipment– Touch its metal chassis or power supply

Keep yourself and equipment connected– Wrist straps and anti-static mats– Static-safe bags

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Static wrist strap

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Typical internal components

Power supply

CD-ROM drive

Hard drive

CPU / fan

Motherboard

Adapter card

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Slide catches

Slide catch, move to open side of case

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Determining which side to open

Ports and connectors attached to motherboard

Open this side to access components

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Removable front cover

Alignment postsAlignment holes

Spring catches

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Activity B-1

Opening the computer case while following proper ESD precautions

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Topic C

Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting

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A PC power supply

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Voltage selection switch

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Typical power requirements

Motherboard 30 W

Memory 10 W / 128 MB

CPU 65 W or more

Hard drive 5 – 15 W

CD-ROM drive 10 – 20 W

Floppy drive 5 – 10 W

Adapter card 5 – 30 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_Good signal

Signals CPU that power is stable and sufficient

+5 V over specific wire Must arrive at correct time

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Peripheral power connector

“Molex” connector

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Floppy power connector

“Berg” connector

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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

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Power supply form factors

ATX/NLX 150 x 140 x 86 millimeters

486 and Pentium PCs

First with soft-power switch and 3.3V

SFX 100 x 125 x 63.5 millimeters

Pentium PCs No -5 V output for ISA cards

WTX 150 x 230 x 86 (single fan)224 x 230 x 86 (double fan)

Pentium PCs No -5 V output for ISA cards

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Activity C-1

Examining a power supplyand connectors

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Topic D

Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting

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Troubleshooting symptoms

Computer fails to boot when powered on, but boots after pressing Ctrl + Alt + Delete

Computer intermittently stops working or reboots

You don’t have sufficient power connectors to connect all the devices you want to install

Computer fails to boot at all, with no lights or beeps; fans don’t start

Computer fails to boot, but fans start

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Activity D-1

Troubleshooting power supply problems

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Unit summary

Measured and described the characteristics of electricity

Identified static electricity and followed ESD safe practices when working with computers

Described the purpose and featurse of power supplies; and installed a new power supply into a PC

Resolved faulty power supply problems