CIS 107a: Introduction to Hardware Concepts

Chapter 2: PC Repair Fundamentals



This chapter is about troubleshooting guidelines. Objectives important to this chapter are:

  1. Tools for working on computers
  2. Preventative maintenance for computers
  3. Procedures for working safely inside a computer
  4. Boot processes
  5. Troubleshooting approaches
  6. Troubleshooting a failed boot

The text presents a list of equipment in terms of need. The first list is considered essential tools. Note: For all tools listed, do not use magnetic tools. These can cause damage to computer equipment and media.The most needed equipment: (Some items are shown in the picture on the right. Hover over the items with your mouse for the items' names.)

  • Phillips-head screwdriver - a couple of sizes here are a good idea
  • Extractor, a spring-loaded device that looks a bit like a hypodermic syringe. Press the plunger and wire prongs come out the other end, that can be used to pick up fallen objects. Sometimes you need this, sometimes you need the tweezers. Sometimes you need the much longer version that is available in automotive stores.
  • Tweezers - for picking pieces of paper out of printers or dropped screws from tight places. Surgical forceps are also good.
  • Flathead screwdriver - a wide blade and a narrow blade are useful.
  • Chip extractor to remove chips - this is not done very often. I would put it in the second or third list
  • Socket drivers for hex nuts and hex screws
  • Bootable rescue disk - this is not as practical if your users use NT or XP workstations. Typically, these OSs require an individual rescue disk for each workstation. (Not shown in this picture.)
  • Ground bracelet and/or ground mat - a good idea, but not used much in the real world. (Not shown in this picture.)
  • Torx screwdrivers - unfortunately, these come in several sizes, and none can be substituted for each other. A good set of them is desirable. (Not shown in this picture.)

If you do not have a tool set, and can only get one, the best thing to have is a Swiss Army Cybertool. I took apart a hard drive with one to make the point that it could be done. Follow the link to see features of one model. Mouse over the components for a description of them.

Equipment that it would be good to have:

  • Cleaning solutions, wipes, etc.
  • Grounding bracelet
  • Multimeter to check the power supply output. Can also be used to check circuit continuity.
  • Can of compressed air, to blow dust out of the computer and components
  • Needle-nose pliers (a locking set of pliers would be worth considering)
  • Flashlight to see inside the PC case (A small Maglite® is handy, because they are durable and you can focus them.)
  • AC outlet ground tester
  • Small cups or bags to help keep screws organized as you work (Note: it would be best to avoid styrafoam cups, due to their tendency to produce static electricity.)
  • Antistatic bags to store unused parts. (Static shielding bags would be better. By the way, Michael Faraday, for whom Faraday cages are named, did not spell his name Farady.)
  • Pen and paper for taking notes
  • Diagnostic cards and diagnostic software
  • Utility software
  • Virus detection software on disks or CD. If Internet connectivity is working, try online scanning instead. (Trend Micro, the maker of PC-cillin. Symantec, the maker of Norton AntiVirus.)

The text recommends some diagnostic hardware and software. It is unlikely that the hardware will be of any use to you, unless you are actually working as a lab or bench technician. A support technician (who goes to users) will find the software of more use. The author discusses a POST (Power On Self Test) diagnostic card. Again, a good idea if you are allowed to use such a device. In a managed environment, this may not be an option.

Recovery CDs are often supplied by computer vendors. They are very useful when software goes bad, but be aware that such CDs are useful only for the devices they are meant for. A recovery CD from any vendor may only be useful for the specific model or specific computer that it came with.

The author offers some sound advice about any PC you are charged with maintaining (professionally or personally):

  • document all changes,
  • make regular backups of data,
  • and protect yourself with anti-virus and firewall programs.

The first idea, documentation, is easy, but most people do not do it. It is easy to write down what you do and to make it a habit to write down all changes to system. It is very unusual to find anyone who does it.

The second idea, making backups, is harder to do, and it is done even less often than documentation. Note that the author recommends making backup copies of your data. It is assumed that you have backup copies of your programs and operating system: they are on your original installation/recovery disks. If your system did not come with such disks, determine whether you can create them from a utility on your hard drive. You will need them when your hard drive eventually dies.

Virus protection software is discussed at length in this edition of the text. Viruses can come in many forms, and by many methods. It is common to receive viruses by e-mail, but it need not be a disaster if you have a good anti-virus program running at all times, and if you receive regular updates to that program. I use Norton Internet Security at home and at work. My system at home is configured to contact Symantec (Norton's publisher) regularly, and to download updates as they become available. This is a recommended configuration.

Firewall software is as important as anti-virus software, especially in environments that provide access to the Internet. The Symantec product mentioned above provides firewall protection, as does the built in program in Windows XP, although the Windows XP program only offers minimal protection from intruders.

Some symptoms that might point to a virus having infected a computer:

  • A program takes longer than normal to load.
  • Disk access times seem excessive for simple tasks.
  • Executable files that once worked no longer work and give unexpected error messages.
  • Unusual error messages occur regularly.
  • Less memory than usual is available.
  • Files disappear mysteriously.
  • There is a noticeable reduction in disk space.
  • Executable files have changed size.
  • The access lights on hard drives and floppy drives turn on when there should be no activity on those devices.
  • You can’t access a drive. This can be a hard drive, CD-ROM drive, Zip drive, or floppy drive.
  • The system won’t boot.
  • Print services are not working properly.

Unfortunately, this list is neither exhaustive, nor definitive. Each of these problems could be caused by something other than a virus, and viruses are not limited to these behaviors. The best procedure to follow when a virus is suspected is to scan the machine with an updated copy of a good anti-virus program. It is often possible to scan the machine across the Internet, which assures you of getting the most current protection available from the anti-virus software publisher. (Trend Micro, the maker of PC-cillin. Symantec, the maker of Norton AntiVirus.) This is often a free service. As such, it is only valid for the scan you make at that time, so buy a copy of a good program for long term protection, and update it regularly.

Some simple precautions will keep you safe from most virus infections:

  • Don't download files except from trusted sources.
  • Scan all files before opening. (Good anti-virus software will do this.)
  • Don't pass floppy disks between users, unless necessary. When you must use floppies, scan them before use.

The text discusses some aspects of physical care of computers. There are some other things to be aware of as well:

  • Temperature and humidity - Most texts recommendhumidity of about 60%. Higher humidity reduces the risk of static electricity. A recommended temperature is not always given. I have just checked the temperature of the server room at the data center where I work, and it has been at about 68 degrees Fahrenheit for the last week. (Computers function better if they are a bit cooler than most humans like it.)
  • Grounding - All electrical equipment should be properly grounded. This includes Uninterruptible Power Supplies.
  • Magnetism - Avoid magnetic fields, for obvious reasons. A technician once told me of a coworker who brought a pair of car stereo speakers into the office. The speakers were placed near a hard drive, and the drive lost its data.
  • Static electricity - ESD, or Electrostatic Discharge, can be a serious cause of problems. Some numbers from a previous text may help you understand the situation:
    • A human can't feel a static discharge until it is 3,000 volts or more.
    • Normal motion, like moving a chair or a foot can generate 1,000 volts.
    • Simply walking across a carpeted area can generate 1,500 to 35,000 volts.
    • Handling a plastic envelope can generate 600 to 7,000 volts.
    • Picking up a plastic bag can generate 1,200 to 20,000 volts.

    Damage can be done to computer parts with 20 to 30 volts. The damage may not cause immediate failure.

    Rules of Static Prevention

    • Ground yourself when working on computers. Use a wrist strap, EXCEPT when working on monitors or power supplies. Test your grounds. Unplug computers, as some modern models pass current through the system when plugged in, even if they are turned off. (This tech I know tried to change sound cards while the new Dell was plugged in...)
    • Do not touch electrical leads.
    • Do not touch ungrounded people while working on components.
    • Use static-shielding bags (gray or silver) not antistatic bags (pink or blue).
    • Keep nonconductors, like styrofoam, away from components. They generate static.
    • Don't place components on metal surfaces.
    • Increase humidity to minimize static.
    • Put the computer on the desk, not the floor. Dry room, winter, feet scuffing on a carpet next to a computer: formula for disaster.
  • Avoid water damage - Read the list above again: get the computer off the floor! If your floors are mopped, electrical equipment needs to be raised out of range of the water.
  • Avoid fires and be able to put them out - Fire extinguishers are classed by the kind of fire they are able to put out. The links below will take you to sites with more information about fire classes and extinguishers. In surveying several sites, I found that there are currently at least four classes of fires, and that the symbols for them have been updated to use pictures instead of letters. Some sites list a Class K for cooking oils (Kitchen fires), but this does not seem to be universal.
  • Air flow - The cover plates on the back of a computer (for expansion cards) should be left in place until they are removed to install a card. If a card is removed, the cover plate should be put back in place.
    If you have an open hole in the computer, you have changed the air flow inside that device. The fans that are meant to cool the computer cannot be expected to pull air through the device as intended if you have essentially cut a hole in the case. Likewise, do not block the intake or output vents for air flow. I have seen users block the intake vents on computers with planters, furniture, books, and more. How did I get to see those computers? I was called because the computers were not working!
  • Clean the computer - computer fans pull in air and pull in dust with it. The dust accumulates, and can cause the computer to get too hot to work. The only time I saw a computer literally crash and burn was when I installed a large network card into an old computer that had not been cleaned in years. I did not check the dust level because the box was very cramped, and I could not see well inside it. (Bad move.) I turned on the device and in moments we had smoke and flames.

Computer technicians will periodically be assigned to transport, retire, and recycle computer equipment. The author provides some good advice about getting a computer ready for these activities:

  • make backups
  • remove removable media
  • power off, and disconnect from electric lines
  • label parts, and make a drawing of how they connect if not standard equipment
  • pack carefully to avoid damage in shipping

Special rules apply to disposal of computer equipment, because some it contains toxic material.

  • batteries (other than alkaline) should go to a recycling center
  • toner cartridges should go to a manufacturer's or vendor's recycling site
  • ink cartridges, motherboards, monitors, and other components should be considered to contain toxic material, and should be turned in to a proper recycling center (Check for periodic events in your community where you can turn in such devices for free or for a small fee)

The text offers a systematic approach to troubleshooting problems. In fact, it is repeated several times in the chapter, so I will try to condense it here.

  • Approach every problem systematically. Be careful, check what you think you know, and don't assume anything.
  • This appears later in the list in the book, but it belongs here: interview the user. Be polite, be helpful, and confirm with the user that you understand their report before moving on. Emphasize that you are collecting the facts, not placing blame. Your duty is to find the truth. What did the user do? How was the system changed since it last worked? Did it ever work? Who else could have used or changed the system?
  • Simplify the problem into components. Check each component, one at a time. For instance, if the user is having a problem, ask what software was running at the time. Remove the programs, one at a time, to test for a conflict or an out-of-memory problem. Alternatively, remove all programs, and add them to the mix, one at a time.
  • Check everything, especially simple things like the computer being turned on and plugged in.
  • Check the simple things first. If you have three things to check, and two will take much less time than the third, save the third for last, unless you really believe that the third item is the real problem.
  • Research for an answer. The Internet has made a lot of difference in what companies offer in terms of support and online documentation.
  • Keep notes about what you do and what you learn. This is for you and for those who follow you. You may need to undo what you try, or you may need to repeat the process.

When testing the problem, some general advice applies to most situations:

  • To test hardware, swap known good for suspected bad. This can backfire: if the problem is the power source and you swap out a damaged component, you may damage the good component. Example: a talented student had a problem with a motherboard. He replaced it with a new one. He neglected to properly insulate it from the metal case of the system unit. The mistake resulted in another lost motherboard.
  • It may be safer to try the alternative version of the advice above: swap suspected bad for known good. If you think a hard drive is bad, put it in place of a good one in another computer. This may prove that the hard drive is not functioning. This technique is less likely to result in damaging good equipment.
  • Don't smoke around the computers - smoke can damage electronic components, and contribute to their failure. I used to know a fellow who smoked in the server room. I think he drives a truck now.
  • Power lines and fluorescent lights - Do not run data cables parallel to fluorescent lights or near power cables. If you must, shield the cables from electromagnetic interference.
  • Avoid excess heat - especially from space heaters and kitchen appliances. Keeping your computer system cool, so that a fire will not ignite, is your most effective form of firefighting: don't let it start.
  • Examine your cables - Once upon a time, I was called to help a user who could not access the network. When I reached his desk, I saw that the network data cable ran from his computer to the floor, under his chair, across the cubicle floor, to a data jack. He had run his wheeled desk chair over the cable and broken it. I ran a new, longer cable from the computer through the channels in the cubicle walls to the data jack. This should never happen: run your cables safely, and keep your users off them.
  • Examine the computer equipment - Most equipment needs to be properly ventilated, kept dry, and kept clean.

This edition of the text offers practical advice and illustrations for servicing a computer. Students should review this section of chapter 2 carefully, especially if they are new to the specific illustrated procedures:

  • opening a computer case
  • removing plastic trim pieces
  • removing (and replacing) data cables
  • removing (and replacing) power cables
  • removing (and replacing) cards
  • removing (and replacing) internal devices

Special care should be taken when removing power supplies and motherboards. Power supplies can be hazardous even when unplugged, and motherboards are difficult to remove and replace without guidance.

The chapter changes topics, discussing the things that take place when a computer is started. When a computer is started (booted), the System BIOS (Basis Input Output System) runs first. This set of programs looks for hardware from which to load the operating system. The operating system provides an interface for the user to control the system. Application software allows the user to perform some sort of work, such as word processing, or creating graphic art.

The BIOS can be configured to always load the operating system from the same device, or to look for it on a series of devices, should the preferred device not be present. Changing the order in which it searches for the OS on these devices is called changing the boot sequence. A technician should be able to make this kind of change to get the computer to boot from a CD, a floppy, or a USB memory device if the hard drive is not functioning properly.

The way your BIOS itself is handled on the system can lead to problems. BIOS chips are ROM chips, which cannot be accessed as quickly as RAM chips, so some systems copy the BIOS to RAM on boot. This is called shadowing ROM or shadow RAM. This can be configured in the CMOS settings. You may want to change this setting (disable it) if the computer is locking up for no apparent reason.

When installing new equipment, you may need to install software (which could include device drivers and application software), and you may need to set what system resources the hardware will use. Resource settings can include combinations of the following:

  • IRQ
  • DMA channel
  • I/O address
  • Memory addresses

An IRQ is a hardware interrupt request line. There are eight, numbered from 0 through 7 on XT class machines, and sixteen of them numbered 0 through 15 on AT (or better) class machines. Assignment to an IRQ gives a device two things: the right to interrupt the processor and request service NOW, and a place in the pecking order of such assignments. 0 is always assigned to the system timer, and it has the highest priority. Other common assignments are shown below.

For older devices, never assign the same interrupt number to two devices that could conceivably need attention at the same time. If possible, do not share interrupts at all. (Note that the system has already done this for IRQs 3 and 4.) However, if you are using USB (Universal Serial Bus) or PCI (Personal Computer Interconnect) devices, these devices are meant to share IRQs. More on this in a later chapter.

IRQs (in order of priority) I/O Address Assignment
0 0040-005F System Timer
1 0060-006F Keyboard Controller
2 00A0-00AF Flows to second IRQ controller. IRQs 8 through 15 come from that controller to this line, then go to the CPU.


0070-007F Real-Time Clock






  SCSI or (Available)


0238-023F Motherboard Mouse Port


00F8-00FF Math Coprocessor


01F0-01F7 Primary IDE drive controller


0170-017F Secondary IDE drive controller
3 details --> COM 2 (02F8-02FF) and COM 4 (02E8-02EF)
4 details --> COM 1 (03F8-03FF) and COM 3 (03E8-03EF)
5 0278-027F LPT 2 or sound card
6 03F0-03F7 Floppy drive controller
7 0378-037F LPT 1

Direct Memory Access (DMA) channels give a device direct access to memory. An XT class machine had channels 0 through 3, later machines have 0 through 7, but you will not be able to use channel 4 since it links the upper channels to the lower ones. NT systems DO NOT want you to use this at all!

I/O Addresses can be compared to a mail drop, a place in memory that the processor will check periodically. This sort of addressing is used for devices that do not need immediate attention from the CPU, whose requests can wait for a cycle or two. Devices should not share addresses, unless confusion and disaster are desired. I/O addresses can also be called ports or sockets.

Memory addresses are sometimes required by a card or device on an older system. Essentially, this RAM is for the use of the device, not for communication with the CPU. The current A+ exams do not test on this concept.

To examine what resources are currently in use (or available) it is suggested that you might use Microsoft Diagnostics (MSD.EXE) for DOS or Windows 9x machines, and Device Manager for computers running Windows 9x and later. The method to get to Device Manager varies a bit in each version of Windows. XP has one more step because it has moved the My Computer icon to the Start menu. (You can put it on the Desktop if you want to from its right-click menu.)

Windows 9x Windows 2000 Windows XP
    Click Start
Right-click My Computer Right-click My Computer Right-click My Computer
Click Properties Click Properties Click Properties
Click Device Manager tab Click Hardware tab Click Hardware tab
  Click Device Manager button Click Device Manager button

Some tips are offered in the chapter for specific troubleshooting.

It is possible that a system problem may come from bad connection of some component. The text recommends removing and replacing components, like expansion cards, making sure that the contacts where they attach are not corroded and that no contact pins are bent or missing. Contacts on expansion cards may be cleaned with a pencil eraser, but care must be taken not to leave bits of rubber on the contacts or in sockets.

It is recommended that you become familiar with the Startup Menu of Windows 9.x and later. Most users never see this menu until something goes wrong with Windows. It is possible to force the menu to appear when Windows boots up by pressing the F8 key while the screen is still black. From the Startup Menu, you may start Windows in Safe Mode, with or without network support, which will be useful in troubleshooting settings in Windows itself.

It is often expedient, when having problems with specific software, to reinstall the software. It may be useful to uninstall the software first, because some installation programs check for installed components, and will not necessarily overwrite a bad or corrupted program file. You are cautioned to back up the user's data first, if at all possible.

It has been common for one Windows program to cause problems with another, because such programs often install components of themselves in the Windows\System directory (or the WinNT\System32 directory, if running Windows NT). The installed components are often DLL files. DLL stands for Dynamic Link Library. A DLL file is like a collection of functions that another program can call. The problem is that one program may install its own version of a DLL file that has the same name as a DLL belonging to another program. It is more common currently for programs to install such files in their own directories, but this problem still comes up.

It is suggested that the most difficult problems to solve are those that are intermittent. Neither you nor the user can predict when the next instance will be, so it is impossible to predict when to be at the user's workstation to diagnose the problem. In such cases, it may be useful to instruct the user in the proper procedure to get a screen dump of any error message he may get. If possible, the screen dump should be sent to a printer, or saved as a file.

Some observations are made about keyboards. Often, a bad keyboard should simply be replaced. If necessary, the text suggests that you can rinse off spilled soft drinks, but the keyboard should dry for a couple of days before you try to use it again. I once turned a keyboard upside down, and not only did spilled coffee drip out of it, but I also saw cigarette ashes and paper clips fall onto the desk. It was a wonder that it worked at all.

Several observations are made about monitor trouble. Often, the user has selected a driver or a combination of settings that do not work with with the monitor and/or video card. Starting a Windows system in Safe Mode will let you load a "plain vanilla" video driver that will work with most monitors and video cards. This will let you test possible combinations of color density, screen resolution, refresh rates, etc. You should be familiar with the procedure to change each of these settings in Windows.

Printer problems are often reported by users. The problem they are having could be an incorrect driver, a printer that needs paper or toner, or a simple jam in the paper path in the printer. Some tips from this section:

  • a printer may give an error message (such as "paper out") if the paper tray is not correctly inserted, or if the sensor for the paper is bent, misaligned, etc.
  • a printer may function improperly if a setting on the tray or in the software does not match the paper size actually being used
  • toner for laser printers may not be totally gone when the printer says it is. You may be able to continue using the same toner cartridge by removing it, shaking it to distribute any existing toner, and replacing the cartridge
  • paper jams can be caused by shreds of paper, labels, or glue that are hidden behind rollers in the printer. Check carefully for debris. Also check for the wrong kind of paper. Paper should generally be 20 pound, and the proper sort for the printer: laser or ink jet type.

A technician is cautioned to keep documentation about equipment. Not only the documentation that comes from the manufacturer, but notes about how the equipment has been configured for the worksite.

It is recommended at the end of the chapter to have backup copies of both your system (and application) software, and your data files. Storing these two kinds of files on different drives is a good idea. Storing data on network servers makes sense, because the data may be backed up centrally instead of relying on a user to make copies.

Fire Extinguishers - A previous edition of the text discussed use and classes of fire extinguishers at this point. Fire extinguishers are classed by the kind of fire they are able to put out. The links below will take you to sites with more information about fire classes and extinguishers. In surveying several sites, I found that there are currently at least four classes of fires, and that the symbols for them have been updated to use pictures instead of letters. Some sites list a Class K for cooking oils (Kitchen fires), but this does not seem to be universal.

Description of Extinguisher Class
Letter and Shape Symbol for Class
Picture for Class
Class A: paper, cloth, wood.
Class B: oil, gasoline, kerosene, propane.
Class C: electrical
Class D: combustible metals, such as magnesium, potassium, sodium
Class K: combustible cooking oils

Information from FEMA

Information from Underwriters Laboratories

Information from the University of Oklahoma Police Department

In most cases, a multiclass extinguisher is preferred. On extinguishers I examined at my workplace, multiple picture symbols were used, showing the pictures for class A, B, and C. (Although they were black and white, not blue, the pictures were the same as those above.)

If the extinguisher is not rated as being effective for a particular class, the symbol or picture will either be missing, or will have a diagonal line drawn through it. Water extinguishers, for example, are not effective against flaming liquids, because the flaming liquid spreads instead of being covered by the water.

While your book does not discuss it, several web sites I encountered discuss a classic explanation of fire. It may be helpful to understand this, the next time you have to put a fire out. For a fire to exist, three factors are needed:

  • oxygen
  • fuel
  • heat

If you can eliminate any one of these factors, the fire will go out. This is why Carbon Dioxide extinguishers work: the CO2 replaces the oxygen in the immediate vicinity of a fire, and the fire stops. Smothering a campfire works about the same way.

A fire break is an example of fighting a fire by depriving it of fuel. Forest fires can be fought this way. Somewhat similarly, I once walked into a rest room in an office and found that someone had placed a roll of toilet paper on top of the light fixture over the sink. I noticed it because it was on fire. I grabbed the roll of paper and tossed it into the sink. This established a fire break. I then put out the fire on the roll of paper with water.

Keeping your computer system cool, so that a fire will not ignite, is your most effective form of firefighting: don't let it start.