Before proceeding to the next chapter, review the following terms and definitions.
Term
Definition
Digital multimeter (DMM)
A tool used to measure electrical voltage, resistance, and current.
Farad
The unit of measurement that is used when measuring capacitance in an electronic component.
Microfarad
One-millionth of a farad. See Farad.
Ohm
The unit of measurement for electronic resistance.
Volt
The unit of measurement for reading AC and DC electricity. The unit of electromotive force equal to a force which, when steadily applied to a conductor whose resistance is one ohm, will produce a current of one ampere.
Watt
The unit of measurement for AC and DC electricity. The amount of power produced in a circuit when a pressure of one volt causes a current of one ampere to flow.
IN BRIEF
If you want to...
Then do this
Check a hard disk for possible bad sectors
Run Scandisk. It will identify any bad sectors and mark them as non-usable if you desire.
Increase the performance of disk reads and writes
Run Defrag. It will optimize the hard drive.
Test the power supply
Power off the system. With a DMM set to DC, check one of the connectors for voltage. You should get -5 VDC or +5 VDC.
CHAPTER QUIZ
Answering these questions will help prepare you for the A+ Certification exams.
A — The Fdisk utility creates the partition and sets the active partition.
A — Power is measured in watts. Amps (short for amperes) is a measure of current, farad is a measure of capacitance, and ohms is a measure of resistance.
B — The most common cause of erratic mouse tracking is dirt. If the driver has failed or the mouse is unplugged, the mouse usually doesn’t work at all.
B — Electrical current is measured in amps.
B — The hard disk partition table is modified with the Fdisk utility and is also used to set the active partition.
C — Electrical capacitance is measured in farads. A microfarad is a portion of a farad.
A — A keyboard error is a hardware error. A keyboard error might generate a 3XX error on the screen, or the POST may recognize that a hardware error has occurred and generate a general hardware error indication with the “Press F1 to Continue” message.
D — Electrical resistance is measure in ohms.
B — A 17XX error indicates hard disk subsystem error.
D — A 1XX error indicates an error in the system board.
A — A 3XX error indicates that a keyboard error has occurred. Typically, a key on the keyboard is stuck.
C — A 6XX error message typically means the floppy disk drive or controller is not operational.
CROSS REFERENCE
For more information about the subjects covered in this chapter, refer to the following pages and chapters in the books listed below.
Upgrading and Repairing PCs, Eighth Edition, Scott Mueller, Que
The Complete PC Upgrade & Maintenance Guide, Eighth Edition, Mark Minasi, Sybex
How Computers Work, Deluxe Edition, Ron White, Ziff-Davis
Most of the topics are also covered in earlier editions of the books, but you may have to look in the index for the correct chapters. Also note that newer technology topics are not covered in the earlier versions of these books.
Topic
Upgrading and Repairing PCs
The Complete PC
How Computers Work
POST error cides
Pages 837-843
Pages 227-235
N/A
Diagnoistics and troubleshooting
Pages 838-986
Pages 202-239
Multimeters
Pages 34-35
pages 887-888
ACTIVITIES
These activities give you the opportunity to see how a DMM can measure both direct and alternating currents. In this activity, you will become familiar with the way a DMM operates. It is imperative that you are familiar with the functions of your DMM so that you do not damage your meter or yourself.
Required Equipment
You need at least one computer with an operating power supply, one wall outlet, a screwdriver, and a DMM to conduct these activities.
Activity 1 — Testing DC Voltage
In this exercise, you will test a power supply for proper DC (direct current) voltage.
Power off the system and remove the outer cover from the PC case.
Find a power supply utility connector that is not in use.
Set the DMM for testing Volts DC and, if scaling is a feature of your DMM, set it to 100 volts.
Power the system on.
Place the black test lead from the DMM in one of the two connections with a black lead.
Place the red lead in the connection with the red wire.
Check the meter reading. It should be registering +5 volts DC.
Reverse the leads.
Check the meter reading. It should be registering -5 volts DC.
Return the leads to the previous position, check again, and notice that the reading is again +5 volts DC.
Place the red lead in the connection with the yellow lead.
Check the meter reading. It should be registering +12 volts DC.
Remove the black lead from the connection and place it against a metal portion of the case housing.
Check the meter reading. It should continue to read +12 volts DC. It shows this reading because the black wire is the ground.
Power off the system, remove the test leads, and replace the cover on the PC.
Activity Review
What two DC voltages should you find on a PC? _________ __________
What color is the ground wire? _____________________________________
Are the voltages always positive (+)? Yes or No
Activity 2 — Testing AC Voltage
In this exercise, you will test an AC (alternating current) power supply for proper AC voltage.
Set the DMM for reading AC voltage and set the scale to the 200 volt scale.
Place the two leads in the two vertical slots of a wall outlet, making sure the two leads do not touch.
Check the meter reading. It should read between 110 volts AC and 125 volts AC.
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