mr. raj’s computer repair i & ii: a+ essentials (701) & computer repair iii & iv...

Mr. RAJ’s Computer Repair I & II: A+ ESSENTIALS (701) & Computer Repair III & IV Practical Applications (702)Contact: 301.802.9066 Email: [email protected] Online Exams: www.Classmarker.com Wiki & Notes: http://mrgupta.wikispaces.com/Designed and prepared for Mr. Raj Students Only at Career Technical Institute [Confidential] Note: Do not copy or distribute without Mr. Raj’s Authorization!

Unit II: Lets discuss the Electricity/ Power Supplies!

Rajeev Gupta (Mr. RAJ)15 Years of IT & Training Experience in Hardware and Networking. Training is my Passion. I am really excited about brining this information to you. I will do my best to give you a perfect place to launch an IT career and I promise it will help you tremendously in knowing how the PC works. You will be building on the foundation no matter where you go. 1

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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



AC/DC• Not an 80’s heavy metal band!

DC AC

A DC current flows in one direction An AC current flows in both directions

The PC’s PSU converts high voltage (230V) AC supplied by the ESBto low voltage DC required by the PC’s motherboard and components



115/230 switch Exam!

Used to switch the PSU between 115 volts and 230 volts



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



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



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



Preventing static buildup• Don’t shuffle your feet• Increase the humidity• Keep yourself grounded• Wear cotton, not

synthetics• Remove carpeting• Use air ionization system

• Design Tech Support Room well

• Discharge static build-up• Anti-static strap• Anti-static mat• Don’t place components on

metal surfaces• Anti-static bags



Preventing static discharge• Equalize charge differences

safely– Unplug the equipment– Touch its metal chassis or power

supply• Keep yourself and equipment

connected– Wrist straps and antistatic mats– Static-safe bags



Power Terms• Joules (J) = Energy• Volts (V) = Voltage (pressure of electrons in the wire)• Amps (A) = Current (amount of electrons moving past a

certain point in the wire)• Watts (W) = Measure of power (how many amps and

volts a device needs to work)• Ohms (Ω) = resistance (how much the wire resists the

flow of electrons)



Surge Suppressors• Protects PC from voltage spikes• Between PC and wall socket• At least 800-1000 Joule(J) rating• Joule = a measure of energy• A higher joule rating means you can be protected

from a more powerful power surge



UPS• Uninterruptable Power Supply• Protects PC from brownouts and blackouts• Two types: Online (UPS) and Standby (SPS)• Most UPSs include surge suppressors• Essentially a sophisticated and big battery• Rated in Watts• NB. Never connect a printer to a UPS

Exam!

Exam!



UPS

UPS

Wall Socket

Sockets

PC

PC

PC

PC



Power Terms - Summary• Pressure = Voltage (V)• Volume Flowing = Amperes (A)• Work = Wattage (W)• Resistance = Ohms (Ω)• Fuses and Ground Wires• An electrical outlet must have a ground wire to be

suitable for PC use Exam!



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



Voltage selection switch

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



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 requirementsMotherboard 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+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



Power connectors Two standards

– Drive power connectors– Motherboard power connectors

Yellow = +12 V Red = +5 V Black = ground



Motherboard power connectors

Dual power connectors

Single power connector



Power supply form factors• Describes size and shape • Must fit:

– Case – Motherboard – Other components

• http://en.wikipedia.org/wiki/Motherboard_form_factor



Wire colors• 20-pin ATX v1.0 single motherboard connector • 24-pin ATX v2.0 motherboard connector

PSU - AT• P8 + P9• Black to Black with the black wires in the centre• AT power switch• Doesn’t support hibernate mode• Wake on modem/LAN not supported



PSU - ATX• Replaced the AT PSU• Used with ATX case and motherboard• P1 power connector• Supplies +3.3V / +2.8V to motherboard• Can’t use an AT PSU with an ATX motherboard and vice versa• “Soft Power”• Constantly supplies 5V to the PC• Never off• Separate on/off switch



Installing a power supply1. Shut down computer2. Unplug computer3. Remove cover from computer4. Disconnect all power wires from components, including motherboard5. Remove retaining screws6. Remove power supply7. Install new power supply and screw it into place8. Connect power wires to components as needed, including motherboard9. Replace cover10.Plug computer into outlet, and boot system to test your work



Function of the PSU• Converts 230V AC to +5V –5V and +12V – 12V DC• Changes from AC to DC• Smoothes out power sags and spikes• Also helps to cool the PC components



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



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 source2. You might need to disconnect the device from its circuit 3. Set the multimeter to read resistance4. Touch the two leads of the multimeter together 5. Touch the black and red probes to either side of the

circuit to be measured6. 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 displayYou 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 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



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


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