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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 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 CD-ROM drive Power supply CPU/fan Adapter card Motherboard Hard drive Slide catches Slide catch, move to open side of case Determining which side to open Open this side to access components Ports and connectors attached to motherboard Removable front cover Alignment holes Alignment posts 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 Yellow 1 4 13, 14, 15 +12 V Red 4 1 (optional) 7, 8, 9 Black 2 and 2 (optional) 3 and 3 Orange Voltage +5 V 4, 5, 6 Ground 10, 11,12 1, 2, 3 +3.3 v Motherboard power connectors Single power connector Dual power connectors (P8/P9) 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. 2. 3. 4. Shut down computer Unplug computer Remove cover from computer 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