Upgrading and Repairing PCs

PC Maintenance Tools

To troubleshoot and repair PC systems properly, you need a few basic tools. If you intend to troubleshoot and repair PCs professionally, there are many more specialized tools you will want to purchase. These advanced tools enable you to more accurately diagnose problems and make jobs easier and faster. The basic tools that should be in every troubleshooter's toolbox are as follows:

• Simple hand tools for basic disassembly and reassembly procedures, including a flat blade and Phillips screwdrivers (both medium and small sizes), tweezers, an IC extraction tool, and a parts grabber or hemostat. Most of these items are included in $10–$20 starter toolkits found at most computer stores.

• Diagnostics software and hardware for testing components in a system.

• A multimeter that provides accurate measurements of voltage and resistance, as well as a continuity checker for testing cables and switches.

• Chemicals, such as contact cleaners; component freeze sprays; and compressed air for cleaning the system.

• Foam swabs, or lint-free cotton swabs if foam isn't available.

• Small nylon wire ties for "dressing" or organizing wires.

Some environments also might have the resources to purchase the following devices, although they're not required for most work:

• Memory-testing machines, used to evaluate the operation of single inline memory modules (SIMMs), dual inline memory modules (DIMMs), Rambus inline memory modules (RIMMs), or double data rate (DDR) DIMMs

• Serial and parallel loopback (or wrap) plugs to test serial and parallel ports

• A network cable scanner (if you work with networked PCs)

• A serial breakout box (if you use systems that operate over serial cables, such as Unix dumb terminals)

• A POST card (if you work with computers running DOS or other non-Windows operating system, you might prefer to get a POST card that can also display IRQs and DMAs in use)

In addition, an experienced troubleshooter will probably want to have soldering and desoldering tools to fix bad serial cables. These tools are discussed in more detail in the following sections.

Hand Tools

When you work with PC systems, the tools required for nearly all service operations are simple and inexpensive. You can carry most of the required tools in a small pouch. Even a top-of-the-line "master mechanics" set fits inside a briefcase-sized container. The cost of these toolkits ranges from about $20 for a small service kit to $500 for one of the briefcase-sized deluxe kits. Compare these costs with what might be necessary for an automotive technician. An automotive service technician would have to spend $5,000–$10,000 or more for a complete set of tools. Not only are PC tools much less expensive, but I can tell you from experience that you don't get nearly as dirty working on computers as you do working on cars.

In this section, you learn about the tools required to assemble a kit that is capable of performing basic, board-level service on PC systems. One of the best ways to start such a set of tools is to purchase a small kit sold especially for servicing PCs.

Figure 23.2 shows some of the basic tools you can find in one of the small PC toolkits that sell for about $20.

Note Some tools aren't recommended because they are of limited use. However, they normally come with these types of kits.

You use nut drivers to remove the hexagonal-headed screws that secure the system-unit covers, adapter boards, disk drives, and power supplies in most systems. The nut drivers work much better than conventional screwdrivers.

Because some manufacturers have substituted Phillips-head screws for the more standard hexagonal-head screws, standard screwdrivers can be used for those systems. If slotted screws are used, they should be removed and replaced with Torx (preferred), hex, or Phillips-head screws that capture the driver tool and prevent it from slipping off the head of the screw. It is especially important never to allow slotted screws to be used on or near a motherboard because a flat-bladed screwdriver can very easily slip and damage the board.

Caution When working in a cramped environment such as the inside of a computer case, screwdrivers with magnetic tips can be a real convenience, especially for retrieving that screw you dropped into the case. However, although I have used these types of screwdrivers many times with no problems, you should be aware of the damage a magnetic field can cause to magnetic storage devices such as floppy disks. Laying the screwdriver down on or near a floppy can damage the data on the disk. Fortunately, floppy disks aren't used that much anymore. Hard drives are shielded by a metal case; CD/DVD drives are not affected because they work optically; and memory and other chips are not affected by magnetic fields (unless they are magnitudes stronger than what you'll see in a hand tool).

Chip-extraction and insertion tools are rarely needed these days because memory chips are mounted on SIMMs, RIMMs, or DIMMs and processors use zero insertion force (ZIF) sockets or other user-friendly connectors. The ZIF socket has a lever that, when raised, releases the grip on the pins of the processor, enabling you to easily lift it out with your fingers.

However, if you work with older systems, you can use a chip extractor to install or remove memory chips (or other smaller chips) without bending any pins on the chip (see Figure 23.3). Usually, you pry out larger chips, such as microprocessors or ROMs, with the small screwdriver. Larger processors up through the 486 might require a chip extractor if they are mounted in the older low insertion force (LIF) socket. These chips have so many pins on them that a large amount of force is required to remove them, despite the fact that they call the socket "low insertion force." If you use a screwdriver on a large physical-size chip such as a 486, you risk cracking the case of the chip and permanently damaging it. The chip extractor tool for removing these chips has a very wide end with tines that fit between the pins on the chip to distribute the force evenly along the chip's underside. This minimizes the likelihood of breakage. Most of these types of extraction tools must be purchased specially for the chip you're trying to remove.

Tip The older-style chip extractor shown on the left in Figure 23.3 does have another use as a keycap extractor. In fact, for this role it works quite well. By placing the tool over a keycap on a keyboard and squeezing the tool so the hooks grab under the keycap on opposite sides, you can cleanly and effectively remove the keycap from the keyboard without damage. This works much better than trying to pry the caps off with a screwdriver, which often results in damaging them or sending them flying across the room.

The tweezers and parts grabber can be used to hold any small screws or jumper blocks that are difficult to hold in your hand. The parts grabber is especially useful when you drop a small part into the interior of a system; usually, you can remove the part without completely disassembling the system (see Figure 23.4).

Finally, the Torx driver is a star-shaped driver that matches the special screws found in most systems (see Figure 23.5). Torx screws are vastly superior to other types of screws for computers because they offer greater grip and the tool is much less likely to slip. The most common cause of new motherboard failures is the use of slotted screwdrivers that slip off the screw head, scratching (and damaging) the motherboard. I never allow slotted screws or a standard flat-bladed screwdriver anywhere near the interior of my systems. You also can purchase tamperproof Torx drivers that can remove Torx screws with the tamper-resistant pin in the center of the screw. A tamperproof Torx driver has a hole drilled in it to allow clearance for the pin. Torx drivers come in a number of sizes, the most common being the T-10 and T-15.

Although this basic set is useful, you should supplement it with some other basic tools, such as

• Electrostatic discharge (ESD) protection kit. This includes a wrist strap and mat (such as those from Radio Shack or Jensen Tools) and prevents static damage to the components on which you are working. These kits consist of a wrist strap with a ground wire and a specially conductive mat with its own ground wire. You also can get just the wrist strap or the antistatic mat separately. In areas or times of the season when there is low humidity, static charges are much more likely to build up as you move, increasing the need for ESD protection. A wrist strap is shown in Figure 23.6.

  Figure 23.6. A typical ESD wrist strap clipped to a nonpainted surface in the case chassis.

  

• Needle-nose pliers and hemostats (curved and straight). These are great for gripping small items and jumpers, straightening bent pins, and so on.

• Electric screwdriver. Combined with hex, Phillips, standard, and Torx bit sets, this tool really speeds up repetitive disassembly/assembly. Black and Decker offers the VersaPak VP730 (www.blackanddecker.com).

• Flashlight. You should preferably use a high-tech LED unit such as those from Lightwave (www.longlight.com), which enable you to see inside dark systems and are easy on batteries.

• Wire cutter or stripper. This is useful for making or repairing cables or wiring. For example, you'd need this (along with a crimping tool) to make 10BASE-T Ethernet cables using UTP cable and RJ45 connectors (see Chapter 20, "Local Area Networking").

• Vise or clamp. This is used to install connectors on cables, crimp cables to the shape you want, and hold parts during delicate operations. In addition to the vise, Radio Shack sells a nifty "extra hands" device that has two movable arms with alligator clips on the end. This type of device is very useful for making cables or for other delicate operations during which an extra set of hands to hold something might be useful.

• Metal file. This is used to smooth rough metal edges on cases and chassis and to trim the faceplates on disk drives for a perfect fit.

• Markers, pens, and notepads. Use these for taking notes, marking cables, and so on.

• Windows 98 Startup Floppy. This has DOS 7.0 and real-mode CD-ROM/DVD drivers, which can be used to boot test the system and possibly load other software.

• Windows 2000/XP original (bootable) CD. This can be used to boot test the system from a CD-ROM/DVD drive, attempt system recovery, OS installation, or to run other software.

• Diagnostics software. This commercial, shareware, or freeware software can be used for PC hardware verification and testing.

• Power on self test (POST) card such as the Post Probe from www.micro2000.com. This is used for displaying POST diagnostics codes on systems with fatal errors.

• Nylon cable-ties. These are used to help in routing and securing cables; neatly routed cables help to improve airflow in the system.

• Digital pocket multimeter (such as those from Radio Shack). This is used for checking power supply voltages, connectors, and cables for continuity.

• Cleaning swabs, canned air (dust blower), and contact cleaner chemicals. These are used for cleaning, lubricating, and enhancing contacts on circuit boards and cable connections. Products include those from www.chemtronics.com, as well as contact enhancer chemicals such as Stabilant 22a (www.stabilant.com).

• Spare CR-2032 lithium coin cell batteries. These are used as the CMOS RAM batteries in most systems, so it is a good idea to have a replacement or two on hand.

Safety

Before working on a system, there are certain safety procedures that should be followed. Some are to protect you, whereas others are to protect the system on which you are working.

From a personal safety point of view, there really isn't that much danger in working on a PC. Even if it is open with the power on, PCs run on only 3.3, 5, and 12 volts, meaning no dangerous, life-threatening voltages are present. However, dangerous voltages do exist inside the power supply and monitor. Most power supplies have 400 volts present at some points internally, and color displays have between 50,000 and 100,000 volts on the CRT! Normally, I treat the power supply and monitor as components that are replaced and not repaired, and I do not recommend you open either of them unless you really know what you are doing around high voltages.

Before working on a PC, you should unplug it from the wall. This is not really to protect you so much as it is to protect the system. A modern ATX form factor system is always partially running—that is, as long as the system is plugged in. So, even if it is off, standby voltages are present. To prevent damage to the motherboard, video card, and other cards, the system should be completely unplugged. If you accidentally turn the system all the way on, and plug in or remove a card, you can fry the card or motherboard.

Electrostatic discharge protection is another issue. While working on a PC, you should wear an ESD wrist strap that is clipped to the chassis of the machine (see Figure 23.6). This ensures that you and the system remain at the same electrical potential and prevents static electricity from damaging the system as you touch it. Some people feel that the system should be plugged in to provide an earth ground. That is not a good idea at all, as I previously mentioned. No "earth" ground is necessary; all that is important is that you and the system remain at the same electrical potential, which is accomplished via the strap. Another issue for personal safety is the use of a commercially available wrist strap, rather than making your own. Commercially made wrist straps feature an internal 1 Meg ohm resistor designed to protect you. The resistor ensures that you are not the best path to ground should you touch any "hot" wire.

When you remove components from the system, they should be placed on a special conductive antistatic mat, which is also a part of any good ESD protection kit. The mat is also connected via a wire and clip to the system chassis. Any components removed from the system, especially items such as the processor, the motherboard, adapter cards, disk drives, and so on, should be placed on the mat. The connection between you, the mat, and the chassis will prevent any static discharges from damaging the components.

Note It is possible (but not recommended) to work without an ESD protection kit if you're disciplined and careful about working on systems. If you don't have an ESD kit available, you can discharge yourself by touching any exposed metal on the chassis or case. Be sure that any system you are working on is unplugged. Many systems today continue to feed power to the motherboard through the motherboard power connection whenever the computer is plugged in, even when the power switch is turned off. Working inside a PC that is still connected to a power source can be very dangerous.

The ESD kits, as well as all the other tools and much more, are available from a variety of tool vendors. Specialized Products Company and Jensen Tools are two of the most popular vendors of computer and electronic tools and service equipment. Their catalogs show an extensive selection of very high-quality tools. (These companies and several others are listed in the Vendor List on the DVD.) With a simple set of hand tools, you will be equipped for nearly every PC repair or installation situation. The total cost of these tools should be less than $150, which is not much considering the capabilities they provide.

A Word About Hardware

This section discusses some problems you might encounter with the hardware (screws, nuts, bolts, and so on) used in assembling a system.

Types of Hardware

One of the biggest aggravations you encounter in dealing with various systems is the different hardware types and designs that hold the units together.

For example, most systems use screws that fit 1/4-inch or 3/16-inch hexagonal nut drivers. IBM used these screws in all its original PC, XT, and AT systems, and most other system manufacturers use this standard hardware as well. Some manufacturers use different hardware, however. Compaq, for example, uses Torx screws extensively in many of its systems. A Torx screw has a star-shaped hole driven by the correct-size Torx driver. These drivers carry size designations such as T-8, T-9, T-10, T-15, T-20, T-25, T-30, and T-40.

A variation on the Torx screw is the tamperproof Torx screw found in power supplies, monitors, hard drives, and other assemblies. These screws are identical to the regular Torx screws, except that a pin sticks up from the middle of the star-shape hole in the screw. This pin prevents the standard Torx driver from entering the hole to grip the screw; a special tamperproof driver with a corresponding hole for the pin is required. An alternative is to use a small chisel to knock out the pin in the screw. Usually, a device sealed with these types of screws is considered to be a replaceable unit that rarely, if ever, needs to be opened.

Caution Note that devices sealed with these types of screws generally have high voltages or other dangers waiting inside, so being able to bypass these screws doesn't mean it's always a good idea. Be sure you know what you are doing before disassembling devices such as monitors and power supplies.

Many manufacturers also use the more standard slotted-head and Phillips-head screws. Slotted-head screws should never be used in a computer because the screwdriver can very easily slip and damage a board. Using tools on these screws is relatively easy, but tools do not grip these fasteners as well as hexagonal head or Torx screws do. In addition, the heads can be stripped more easily than the other types. Extremely cheap versions tend to lose bits of metal as they're turned with a driver, and the metal bits can fall onto the motherboard. Stay away from cheap fasteners whenever possible; the headaches of dealing with stripped screws aren't worth it.

Some system manufacturers now use cases that snap together or use thumb screws. These are usually advertised as "no-tool" cases because you literally do not need any tools to remove the cover and access the major assemblies.

To make an existing case tool-free, you can replace the normal case screws with metal or plastic thumbscrews. However, you still should always use metal screws to install internal components, such as adapter cards, disk drives, power supplies, and the motherboard, because the metal screws provide a ground point for these devices.

English Versus Metric

Another area of aggravation with hardware is the fact that two types of thread systems exist: English and metric. IBM used mostly English-threaded fasteners in its original line of systems, but many other manufacturers used metric-threaded fasteners.

The difference between the two becomes especially apparent with disk drives. American-manufactured drives typically use English fasteners, whereas drives made in Japan, Taiwan, and other Pacific Rim countries (where most disk drives are now made) usually use metric. Whenever you replace a floppy drive in an older PC, you encounter this problem. Try to buy the correct screws and any other hardware, such as brackets, with the drive because they might be difficult to find as separate items. Many drive manufacturers offer retail drive kits that include all the required mounting components. The OEM's drive manual lists the correct data about a specific drive's hole locations and thread size.

Tip Before you discard an obsolete computer, remove the screws and other reusable parts, such as cover plates, jumper blocks, and so on. Label the bag or container with the name and model of the computer to help you more easily determine where else you can use the parts later.

Hard disks can use either English or metric fasteners; check your particular drive to see which type it uses. Most drives today use metric hardware.

Caution Some screws in a system can be length-critical, especially screws used to retain hard disk drives. You can destroy some hard disks by using a mounting screw that's too long; the screw can puncture or dent the sealed disk chamber when you install the drive and fully tighten the screw. When you install a new drive in a system, always make a trial fit of the hardware to see how far the screws can be inserted into the drive before they interfere with its internal components. When in doubt, the drive manufacturer's OEM documentation will tell you precisely which screws are required and how long they should be. Most drives sold at retail include correct-length mounting screws, but OEM drives usually don't include screws or other hardware.

Soldering and Desoldering Tools

In certain situations—such as repairing a broken wire, making cables, reattaching a component to a circuit board, removing and installing chips that are not in a socket, and adding jumper wires or pins to a board—you must use a soldering iron to make the repair.

Although virtually all repairs these days are done by simply replacing the entire failed board and many PC technicians never touch a soldering iron, you might find one useful in some situations. The most common case is when physical damage to a system has occurred, such as when someone rips the keyboard connector off a motherboard by pulling on the cable improperly. Simple soldering skills can save the motherboard in this case.

Most motherboards these days include I/O components, such as serial and parallel ports. Many of these ports are fuse-protected on the board; however, the fuse is usually a small soldered-in component. These fuses are designed to protect the motherboard circuits from being damaged by an external source. If a short circuit or static charge from an external device blows these fuses, the motherboard can be saved if you can replace them.

To perform minor repairs such as these, you need a low-wattage soldering iron—usually about 25 watts. More than 30 watts generates too much heat and can damage the components on the board. Even with a low-wattage unit, you must limit the amount of heat to which you subject the board and its components. You can do this with quick and efficient use of the soldering iron and with the use of heatsinking devices clipped to the leads of the device being soldered. A heatsink is a small metal clip-on device designed to absorb excessive heat before it reaches the component the heatsink is protecting. In some cases, you can use a pair of hemostats as an effective heatsink when you solder a component.

To remove components soldered into place on a printed circuit board, you can use a soldering iron with a solder sucker. This device normally takes the form of a small tube with an air chamber and a plunger-and-spring arrangement. (I do not recommend the squeeze-bulb type of solder sucker.) The unit is "cocked" when you press the spring-loaded plunger into the air chamber. When you want to remove a device from a board, you use the soldering iron from the underside of the board and heat the point at which one of the component leads joins the circuit board until the solder melts. As soon as melting occurs, move the solder-sucker nozzle into position and press the actuator. When the plunger retracts, it creates a momentary suction that draws the liquid solder away from the connection and leaves the component lead dry in the hole.

Always perform the heating and suctioning from the underside of a board, not from the component side. Repeat this action for every component lead joined to the circuit board. When you master this technique, you can remove a small component in a minute or two with only a small likelihood of damage to the board or other components. Larger chips that have many pins can be more difficult to remove and resolder without damaging other components or the circuit board.

Tip These procedures are intended for "through-hole" devices only. These are components whose pins extend all the way through holes in the board to the underside. Surface-mounted devices are removed with a completely different procedure, using much more expensive tools. Working on surface-mounted components is beyond the capabilities of all but the most well-equipped shops.

If you intend to add soldering and desoldering skills to your arsenal of abilities, you should practice. Take a useless circuit board and practice removing various components from the board; then, reinstall the components. Try to remove the components from the board by using the least amount of heat possible. Also, perform the solder-melting operations as quickly as possible, limiting the time the iron is applied to the joint. Before you install any components, clean out the holes through which the leads must project and mount the component in place. Then, apply the solder from the underside of the board, using as little heat and solder as possible.

Attempt to produce joints as clean as the joints the board manufacturer produced by machine. Soldered joints that do not look clean can keep the component from making a good connection with the rest of the circuit. This "cold-solder joint" is normally created because you have not used enough heat. Remember that you should not practice your new soldering skills on the motherboard of a system you are attempting to repair! Don't attempt to work on real boards until you are sure of your skills. I always keep a few junk boards around for soldering practice and experimentation.

Tip When first learning to solder, you might be tempted to set the iron on the solder and leave it there until the solder melts. If the solder doesn't melt immediately when you apply the iron to it, you're not transferring the heat from the iron to the solder efficiently. This means that either the iron is dirty or there is debris between it and the solder. To clean the iron, take a wet sponge and drag it across the tip of the iron. If after cleaning the iron, there's still some resistance, try to scratch the solder with the iron when it's hot. Generally, this removes any barriers to heat flow and instantly melts the solder.

No matter how good you get at soldering and desoldering, some jobs are best left to professionals. Components that are surface-mounted to a circuit board, for example, require special tools for soldering and desoldering, as do other components that have high pin densities.

Test Equipment

In some cases, you must use specialized devices to test a system board or component. This test equipment is not expensive or difficult to use, but it can add much to your troubleshooting abilities.

Electrical Testing Equipment

I consider a voltmeter to be required gear for proper system testing. A multimeter can serve many purposes, including checking for voltage signals at various points in a system, testing the output of the power supply, and checking for continuity in a circuit or cable. An outlet tester is an invaluable accessory that can check the electrical outlet for proper wiring. This capability is useful if you believe the problem lies outside the computer system.

Loopback Connectors (Wrap Plugs)

For diagnosing serial- and parallel-port problems, you need loopback connectors (also called wrap plugs), which are used to circulate, or wrap, signals (see Figure 23.7). The plugs enable the serial or parallel port to send data to itself for diagnostic purposes.

Various types of loopback connectors are available. To accommodate all the ports you might encounter, you need one for the 25-pin serial port, one for the 9-pin serial port, and one for the 25-pin parallel port. Many companies, including IBM, sell the plugs separately, but be aware that you also need diagnostic software that can use them. Some diagnostic software products, such as Micro 2000's Micro-Scope, include loopback connectors with the product, or you can purchase them as an option for about $30 a set. Note that there are some variations on how loopback connectors can be made, and not all versions work properly with all diagnostics software. You should therefore use the loopback connectors recommended by the diagnostics software you will be using.

IBM sells a special combination plug that includes all three connector types in one compact unit. The device costs about the same as a normal set of wrap plugs. If you're handy, you can even make your own wrap plugs for testing. I include wiring diagrams for the three types of wrap plugs in Chapter 17, "I/O Interfaces from Serial and Parallel to IEEE-1394 and USB." In that chapter, you also will find a detailed discussion of serial and parallel ports.

Besides simple loopback connectors, you also might want to have a breakout box for your toolkit. A breakout box is a DB25 connector device that enables you to make custom temporary cables or even to monitor signals on a cable. For most PC troubleshooting uses, a "mini" breakout box works well and is inexpensive.

Meters

Some troubleshooting procedures require that you measure voltage and resistance. You take these measurements by using a handheld Digital Multi-Meter (DMM). The meter can be an analog device (using an actual meter) or a digital-readout device. The DMM has a pair of wires called test leads or probes. The test leads make the connections so that you can take readings. Depending on the meter's setting, the probes measure electrical resistance, direct-current (DC) voltage, or alternating-current (AC) voltage. Figure 23.8 shows a typical DMM being used to test the +12V circuit on an ATX motherboard.

Usually, each system-unit measurement setting has several ranges of operation. DC voltage, for example, usually can be read in several scales, to a maximum of 200 millivolts (mV), 2V, 20V, 200V, and 1,000V. Because computers use both +5V and +12V for various operations, you should use the 20V maximum scale for making your measurements. Making these measurements on the 200mV or 2V scale could "peg the meter" and possibly damage it because the voltage would be much higher than expected. Using the 200V or 1,000V scale works, but the readings at 5V and 12V are so small in proportion to the maximum that accuracy is low.

If you are taking a measurement and are unsure of the actual voltage, start at the highest scale and work your way down. Most of the better meters have autoranging capability—the meter automatically selects the best range for any measurement. This type of meter is much easier to operate. You simply set the meter to the type of reading you want, such as DC volts, and attach the probes to the signal source. The meter selects the correct voltage range and displays the value. Because of their design, these types of meters always have a digital display rather than a meter needle.

Caution Whenever you are using a multimeter to test any voltage that could potentially be 50V or above (such as AC wall socket voltage), always use one hand to do the testing, not two. Either clip one lead to one of the sources and probe with the other or hold both leads in one hand. If you hold a lead in each hand and accidentally slip, you can very easily become a circuit, allowing power to conduct or flow through you. When power flows from arm to arm, the path of the current is directly across the heart. The heart muscle tends to quit working when subjected to high voltages. They're funny that way.

I prefer the small digital meters; you can buy them for only slightly more than the analog style, and they're extremely accurate and much safer for digital circuits. Some of these meters are not much bigger than a cassette tape; they fit in a shirt pocket. Radio Shack sells a good unit in the $25 price range; the meter (refer to Figure 23.8) is a half-inch thick, weighs 3 1/2 ounces, and is digital and autoranging, as well. This type of meter works well for most, if not all, PC troubleshooting and test uses.

Caution You should be aware that many analog meters can be dangerous to digital circuits. These meters use a 9V battery to power the meter for resistance measurements. If you use this type of meter to measure resistance on some digital circuits, you can damage the electronics because you essentially are injecting 9V into the circuit. The digital meters universally run on 3V–5V or less.

Logic Probes and Logic Pulsers

A logic probe can be useful for diagnosing problems in digital circuits (see Figure 23.9). In a digital circuit, a signal is represented as either high (+5V) or low (0V). Because these signals are present for only a short time (measured in millionths of a second) or oscillate (switch on and off) rapidly, a simple voltmeter is useless. A logic probe is designed to display these signal conditions easily.

Logic probes are especially useful for troubleshooting a dead system. By using the probe, you can determine whether the basic clock circuitry is operating and whether other signals necessary for system operation are present. In some cases, a probe can help you cross-check the signals at each pin on an integrated circuit chip. You can compare the signals present at each pin with the signals a known-good chip of the same type would show—a comparison that is helpful in isolating a failed component. Logic probes also can be useful for troubleshooting some disk drive problems by enabling you to test the signals present on the interface cable or drive-logic board.

A companion tool to the probe is the logic pulser. A pulser is designed to test circuit reaction by delivering a logical high (+5V) pulse into a circuit, usually lasting from 1 1/2 to 10 millionths of a second. Compare the reaction with that of a known-functional circuit. This type of device normally is used much less frequently than a logic probe, but in some cases it can be helpful for testing a circuit.

Outlet Testers

Outlet testers are very useful test tools. These simple, inexpensive devices, sold in hardware stores, test electrical outlets. You simply plug in the device, and three LEDs light up in various combinations, indicating whether the outlet is wired correctly (see Figure 23.10).

Although you might think that badly wired outlets would be a rare problem, I have seen a large number of installations in which the outlets were wired incorrectly. Most of the time, the problem is in the ground wire. An improperly wired outlet can result in unstable system operation, such as random parity checks and lockups. With an improper ground circuit, currents can begin flowing on the electrical ground circuits in the system. Because the system uses the voltage on the ground circuits as a comparative signal to determine whether bits are 0 or 1, a floating ground can cause data errors in the system.

Caution Even if you use a surge protector, it will not protect your system from an improperly wired outlet. Therefore, you still should use an outlet tester to ensure your outlet is computer friendly.

Once, while running one of my PC troubleshooting seminars, I used a system that I literally could not approach without locking it up. Whenever I walked past the system, the electrostatic field generated by my body interfered with the system and the PC locked up, displaying a parity-check error message. The problem was that the hotel at which I was giving the seminar was very old and had no grounded outlets in the room. The only way I could prevent the system from locking up was to run the class in my stocking feet because my leather-soled shoes were generating the static charge.

Other symptoms of bad ground wiring in electrical outlets are continual electrical shocks when you touch the case or chassis of the system. These shocks indicate that voltages are flowing where they should not be. This problem also can be caused by bad or improper grounds within the system. By using the simple outlet tester, you can quickly determine whether the outlet is at fault.

If you just walk up to a system and receive an initial shock, it's probably only static electricity. Touch the chassis again without moving your feet. If you receive another shock, something is very wrong. In this case, the ground wire actually has voltage applied to it. You should have a professional electrician check the outlet immediately.

If you don't like being a human rat in an electrical experiment, you can test the outlets with your multimeter. First, remember to hold both leads in one hand. Test from one blade hole to another. This should read between 110V and 125V, depending on the electrical service in the area. Then, check from each blade to the ground (the round hole). One blade hole, the smaller one, should show a voltage almost identical to the one you got from the blade-hole–to–blade-hole test. The larger blade hole when measured to ground should show less than 0.5V.

Because ground and neutral are supposed to be tied together at the electrical panel, a large difference in these readings indicates that they are not tied together. However, small differences can be accounted for by current from other outlets down the line flowing on the neutral, when there isn't any on the ground.

If you don't get the results you expect, call an electrician to test the outlets for you. More weird computer problems are caused by improper grounding and other power problems than people like to believe.

Memory Testers

I now consider a memory test machine an all-but-mandatory piece of equipment for anyone serious about performing PC troubleshooting and repair as a profession. The tester is a small device designed to evaluate SIMMs, DIMMs, RIMMs, and other types of memory modules, including individual chips such as those used as cache memory. These testers can be somewhat expensive, costing upward of $1,000–$2,500 or more, but these machines are the only truly accurate way to test memory.

Without one of these testers, you are reduced to testing memory by running a diagnostic program on the PC and testing the memory as it is installed. This can be very problematic because the memory diagnostic program can do only two things to the memory: write and read. A SIMM/DIMM/RIMM tester can do many things a memory diagnostic running in a PC can't do, such as

• Identify the type of memory

• Identify the memory speed

• Identify whether the memory has parity or is using bogus parity emulation

• Vary the refresh timing and access speed timing

• Locate single bit failures

• Detect power- and noise-related failures

• Detect solder opens and shorts

• Isolate timing-related failures

• Detect data retention errors

No conventional memory diagnostic software can do these things because it must rely on the fixed access parameters set up by the memory controller hardware in the motherboard chipset. This prevents the software from being capable of altering the timing and methods used to access the memory. You might have memory that fails in one system and works in another when the chips are actually bad. This type of intermittent problem is almost impossible to detect with diagnostic software.

The bottom line is that there is no way you can test memory with true accuracy while it is installed in a PC; a memory tester is required for comprehensive and accurate testing. The price of a memory tester can be justified very easily in a shop environment where a lot of PCs are tested because many software and hardware upgrades today require the addition of new memory. With the large increases in the amount of memory in today's systems and the stricter timing requirements of newer motherboard designs, it has become even more important to be able to identify or rule out memory as a cause of system failure. One company manufacturing memory testers I recommend is Tanisys Technology; its Darkhorse Systems line of memory testers can handle virtually every type of memory on the market. See the Vendor List on the DVD for more information. Also, see Chapter 6, "Memory," for more information on memory in general.

Special Tools for the Enthusiast

All the tools described so far are commonly used by most technicians. However, a few additional tools do exist that a true PC enthusiast might want to have.

Electric Screwdriver

Perhaps the most useful tool I use is an electric screwdriver. It enables me to disassemble and reassemble a PC in record time and makes the job not only faster but easier as well. I like the type with a clutch you can use to set how tight it will make the screws before slipping; such a clutch makes it even faster to use. If you use the driver frequently, it makes sense to use the type with replaceable, rechargeable batteries, so when one battery dies you can quickly replace it with a fresh one.

Caution Note that using an electric screwdriver when installing a motherboard can be dangerous because the bit can easily slip off the screw and damage the board. A telltale series of swirling scratches near the screw holes on the board can be the result, for which most manufacturers rightfully deny a warranty claim. Be especially careful if your motherboard is retained with Phillips-head screws because they are extremely easy for the bit to slip out of. Normally, I recommend using only Torx-head or hex-head screws to retain the motherboard because they are far more resistant to having the bit slip out and cause damage.

With the electric screwdriver, I recommend getting a complete set of English and metric nut driver tips as well as various sizes of Torx, flat-head, and Phillips-head screwdriver tips.

Tamperproof Torx Bits

As mentioned earlier, mA Any devices such as power supplies and monitors are held together with tamperproof Torx screws. Tamperproof Torx driver sets are available from any good electronics tool supplier.

Temperature Probe

Determining the interior temperature of a PC is often useful when diagnosing whether heat-related issues are causing problems. This requires some way of measuring the temperature inside the PC, as well as the ambient temperature outside the system. The simplest and best tool I've found for the job is the digital thermometers sold at most auto parts stores for automobile use. They are designed to read the temperature inside and outside the car and normally come with an internal sensor, as well as one at the end of a length of wire.

With this type of probe, you can run the wired sensor inside the case (if it is metal, make sure it does not directly touch the motherboard or other exposed circuits where it might cause a short) with the wires slipped through a crack in the case or out one of the drive bays. Then, with the system running you can take the internal temperature as well as read the room's ambient temperature. Normally, the maximum limit for internal temperature should be 110°F (43°C) or less. If your system is running near or above that temperature, problems can be expected. You also can position the probe in the system to be near any heat producing devices, such as the processor, video card, and so on, to see the effect of the device. Probing the temperature with a device such as this enables you to determine whether additional cooling is necessary (that is, adding more cooling fans to the case) and enables you to check to see whether the added fans are helping.

Infrared Thermometer

Another useful temperature tool is a noncontact infrared (IR) thermometer, which is a special type of sensor that can measure the temperature of an object without physically touching it (see Figure 23.11). You can take the temperature reading of an object in seconds by merely pointing the handheld device at the object you want to measure and pulling a trigger.

An IR thermometer works by capturing the infrared energy naturally emitted from all objects warmer than absolute zero (0° Kelvin). Infrared energy is a part of the electromagnetic spectrum with a frequency below that of visible light, which means it is invisible to the human eye. Infrared wavelengths are between 0.7 microns and 1,000 microns (millionths of a meter), although infrared thermometers typically measure radiation in the range 0.7–14 microns.

Because IR thermometers can measure the temperature of objects without touching them, they are ideal for measuring chip temperatures in a running system—especially the temperature of the CPU heatsink. By merely pointing the device at the top of the CPU and pulling the trigger, you can get a very accurate measurement in about 1 second. To enable more accuracy in positioning, many IR thermometers incorporate a laser pointer, which is used to aim the device.

IR thermometers are designed to measure IR radiation from a device; they can't be used to measure air temperature. The sensors are specifically designed so that the air between the sensor and target does not affect the temperature measurement.

Although several IR thermometers are available on the market, I use and recommend the Raytek (www.raytek.com) MiniTemp series, which consists of the MT2 and MT4. Both units are identical, but the MT4 includes a laser pointer for aiming. The MT2 and MT4 are capable of measuring temperatures between 0° and 500°F (-18°–260°C) in one half of a second with an accuracy of about plus or minus 3°F (2°C). They cost $80–$100 and are available from NAPA auto parts stores (these devices have many uses in automotive testing as well) and other tool outlets.

Large Claw-Type Parts Grabber

One of the more useful tools in my toolbox is a large claw-type parts grabber, normally sold in stores that carry automotive tools. Having one of these around has saved many hours of frustration digging back into a system or behind a desk for a loose or dropped screw.

These grabbers are very similar to the small claw-type grabber included with most PC toolkits, except they are much larger—normally two feet or so in length. They can be useful if you drop a screw down inside a tower case, or even on the floor under or behind a desk or cabinet. Although magnetic parts grabbers are also available, I normally recommend the claw-type because using a powerful magnet near a computer can cause problems with any disk storage media you have about, or even the hard disk or CRT-type display.