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

Topic A

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

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

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

Characteristics, continued

Resistance — Force that opposes the flow of DC through a conductor – Measured in ohms (Ω)

Impedance — Like resistance, but applies to AC

Power – Measured in watts– Calculate by multiplying voltage by current

Energy — Electrical power delivered over time

Activity A-1

Examining the characteristics of electricity

Electricity

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

V = i * r Resistance of the human body is

about 500 KΩ (500,000 Ω)

Safety precautions

Don’t touch exposed contacts Touch only insulated handles of tools Leave covers on equipment Work one-handed Don’t insert anything into wall outlets Remove jewelry, watches, etc. Keep hands clean and dry Don’t work in wet surroundings

Activity A-2

Considering electrical safety

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– 30 volts can damage electronics

Preventing static buildup

Don’t shuffle your feet Increase the humidity: 50-60% Keep yourself grounded Wear cotton, not synthetics Remove carpeting Use air ionization system

Preventing static discharge

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

Keep yourself and equipment connected together– Wrist straps and antistatic mats– Static-safe bags

Goal is to be at a charge potential that’s equal with the device you’re servicing (not with ground)

Service on a properly grounded bench

Antistatic (ESD) wrist straps

Typical internal components

Power supply

CD-ROM drive

Hard drive

CPU/fan

Motherboard

Adapter card

Slide catch, move to open side of case

Slide catches

Determining which side to open

Ports and connectors attached to motherboard

Open this side to access components

Removable front cover

Alignment postsAlignment holes

Spring catches

Activity A-3

Opening the computer case while following proper ESD precautions

Topic B

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

PC power supply

Converts AC wall voltage to DC voltages for PC components

Includes a fan Provides some conditioning functions Can maintain power during brief drops and

outages

Power supply specifications

Rated by DC power output in watts– Modern systems typically =>300 watts– Older systems <200 watts

Rating isn’t an indicator of power draw– Draws only the power needed to supply

internal components

Typical power requirements

Motherboard 30 W

Memory 10 W per 2 GB

CPU 45–145 W or more

Hard drive 5–15 W

CD-ROM drive 5–20 W

Floppy drive 5–10 W

Adapter card 5–30 W

Standard outputs

+/- 5 V +/- 12 V + 3.3 V

Power connectors

Two standards– Drive power connectors– Motherboard power connectors

Peripheral power connector

Molex connector Typically used to connect hard drives and

optical drives

Floppy power connector

Berg connector Smaller than Molex Typically used to connect floppy drives

SATA power connector

New, for Serial ATA drives

Wire colors

Wire color Molex Berg SATA Voltage

Yellow 1 4 13, 14, 15 +12 V

Red 4 1 (optional) 7, 8, 9 +5 V

Black 2 and 3

2 (optional) and 3

4, 5, 610, 11,12

Ground

Orange 1, 2, 3 +3.3 v

Motherboard power connectors

Dual power connectors (P8/P9)

Single power connector

Power supply form factors

Describes size and shape Must fit:

– Case – Motherboard – Other components

Activity B-1

Identifying your computer’s power supply

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

Selecting the voltage

Set power supply to run on 110-120 VAC or 220-240 VAC

With computer off, slide switch Usually located near power cord port

continued

Selecting the voltage, continued

Improperly set voltage, can cause computer to:– Fail to turn on– Operates improperly– Incur serious damage

www.voltagevalet.com/elec_guide.html

Activity B-2

Installing a new power supply

Topic C

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

An AC signal

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)

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

Activity C-1

Discussing power conditioning equipment

Electrical measurements

Measure electrical values with a multimeter

Multimeters can be digital or analog Use to measure

– Resistance– Voltage– Current– Continuity

Measuring resistance

1. Turn off the device you’re 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 meter’s display

Measuring voltage

1. Verify the power supply is on

2. Set your multimeter to read either DC or AC voltage

3. Touch the black probe to the ground, and touch the red probe to the spot where you want to measure the voltage

4. Read the voltage from the meter’s display

You must exercise care when taking voltage readings as the computer is powered up

Measuring current

Break the circuit and insert the meter in the break

Ammeter doesn’t require break Clamp ammeters are often used to

measure current flow in 110 V and higher circuits

Measuring continuity

Set your multimeter to display resistance (ohms) and look for circuits with zero resistance

Also can use continuity mode, if available

Power supply tester

Alternative to manual test with multimeter

Takes approximately 30 minutes

Follow instructions for your specific tester

Advantages:– Less susceptible to human

error– Results are more conclusive– Safer to perform

Activity C-2

Measuring electrical values

Power supply problems

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

Computer intermittently stops working or reboots

You don’t have enough power connectors for all the devices you want to install

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

Computer fails to boot, but fans start

The Power_Good signal

Signals CPU that power is stable and sufficient

+5 V over specific wire Must arrive at correct time

Activity C-3

Troubleshooting power supply problems

Electricity and power supplies

Identified electrostatic discharge, and followed ESD safe practices while working with computer components

Installed a new power supply in a PC Resolved problems with faulty power

supplies