PC Hardware in a Nutshell, 3rd Edition [Electronic resources] نسخه متنی

2.3 General Procedures

After you
assemble a toolkit with the hand tools and utilities described in the
preceding sections, you have everything you need to upgrade or repair
a PC, except for the new components. Before you get started, take a
few minutes to read through the following sections, which describe
the common procedures and general knowledge you need to work on PCs.
These sections describe the general tasks you perform almost anytime
you work on a computerthings such as opening the case, setting
jumpers and switches, manipulating cables, and adding or removing
expansion cards. Instructions for specific tasks such as replacing a
motherboard, disk drive, or power supply are given in the relevant
chapters.

2.3.1 Before You Open the Case

Although
you may be raring to get in there and fix something, taking the time
to prepare properly before you jump in pays big dividends later.
Before you open the case, do the following:

The old saying,
"If all you have is a hammer, everything looks like
a nail" is nowhere truer than with PC repairs. Just
as surgeons are often accused of being too ready to cut, PC
technicians are always too ready to pop the lid. Before you assume
that hardware is causing the problem, make sure the problem
isn't being caused by an application, by Windows, or
by a virus. Use your hardware diagnostic utility and virus scanner

before you assume the hardware is at fault and
start disconnecting things.

Inexperienced technicians dive in willy-nilly without thinking things
through first. Experienced ones first decide what is the most likely
cause of the problem, what can be done to resolve it, in what order
they should approach the repair, and what they'll
need to complete it. Medical students have a saying:
"When you hear thundering hooves,
don't think about zebras." In
context, that means that you should decide the most likely causes of
the problem in approximate ranked order, decide which are easy to
check for, and then eliminate the easy ones first. In order, check
easy/likely, easy/unlikely, hard/likely, and finally hard/unlikely.
Otherwise, you may find yourself tearing down a PC and removing the
video card before you notice that someone unplugged the monitor.

Every time you pop the cover of a PC,
there's a small but ever-present risk that something
that used to work won't work when you put everything
together again. One of the wires in a cable may be hanging by a
thread, or the hard drive may be teetering on the edge of failure.
Just opening the case may cause a marginal component to fail
irreversibly. So, before you even think of doing PC surgery, make
sure the hard drive is backed up.

It's
important to have a record of the CMOS settings before you open the
case. Working on a PC doesn't normally affect CMOS
settings, but some activities (e.g., flashing the BIOS, removing the
battery, or shorting the CMOS clear jumper) can wipe out all
settings. If that happens, you'll need to re-enter
the settings, and you'd better have them available.
Recording CMOS settings is particularly important when
you're not replacing the motherboard because
they're the ones you'll continue to
use. If you are replacing the motherboard, the only CMOS settings you
need to record are those that specify the hard disk geometry. Even if
you don't plan to do anything that might affect
CMOS, use your CMOS save/restore utility to save these settings to a
diskette before you open the case. If you don't have
such a utility, download one or record the settings with pencil and
paper.

It may seem obvious, but you
need to disconnect all external cables before you can move the PC
itself to the operating room. Many PCs are located under desks or are
positioned so as to make it difficult to see the rear panel. If
necessary, get down on the floor and crawl behind the PC with a
flashlight to make sure it isn't still tethered to
something. We've dragged modems, keyboards, and mice
off desks because we weren't paying attention, and
we once came within inches of pulling a $2,000 monitor onto the
floor. Check the cables or pay the price.

Monitors are not only fragile, but also can cause serious injuries if
the tube implodes. A monitor on the floor is an accident waiting to
happen. If you're not taking the monitor to the work
area, keep it on the desk out of harm's way. If you
must put it on the floor, at least turn the screen toward the
wall.

2.3.2 Electrostatic Discharge (ESD) Precautions

You've
probably been startled by a static electric shock on a dry winter
day. This phenomenonformally called electrostatic
discharge
(ESD)can destroy sensitive PC
components instantly. Just because you don't notice
it doesn't mean it isn't there,
either. Static potential must build to several thousand volts before
you experience a shock, but levels of only a few hundred volts are
hazardous for PCs. Worse, incremental damage may occur invisibly and
is cumulative, so although any one zap may not kill a component
outright, it will surely damage it and make it that much more prone
to fail later on.

Although this may be off-putting, it's really no big
deal. We've worked on hundreds of PCs over the
years, and haven't damaged one yet, so far as we
know. You can easily avoid problems with static electricity by
following three rules: (1) don't wear rubber-soled
shoes or synthetic clothing, (2) work in an uncarpeted area, and (3)
ground yourself to dissipate the static charge each time you are
about to touch a PC component.

The
first generally recommended line of defense against static is an
antistatic wrist strap. One end wraps around
your wrist. The other end may have alligator clips intended to
connect to the PC case or power supply, or it may have a plug
intended to fit a standard power receptacle. You can buy these things
for a few dollars from most mail-order places. They are sometimes
included with expensive chips such as processors. We
don't like these straps. They're
awkward to work with, andalthough we know it is
safeconnecting a conductive strap to your wrist and then
plugging it into the wall seems a bit outré.

We use a simpler method. It protects sensitive components just as
reliably, as long as you get in the habit of following it
religiously. Leave the PC you're working on plugged
in, which ensures that it is grounded (although it's
a good idea to use a switched-off power strip, as described earlier
in this chapter). When you first sit down to work on the PC, and then
each time you are about to touch a static-sensitive component, touch
the chassis or power supply to dissipate the accumulated static
charge. When we're working on a particularly
sensitive or expensive component, like a CPU, we actually keep our
left hand on the chassis the whole time we're in
contact with the component. Note that ATX motherboards maintain
constant low voltage, even when the system is turned off. For that
reason, either disconnect the power cord before working on an ATX
system or connect it to a switched-off power strip. Touching the
power supply still works, however, as it provides an adequate sink
for static charges.

To minimize problems with static electricity, buy a spray/mister bottle at the hardware store or supermarket. Fill it with water and add a few drops of dishwashing liquid or fabric softener. Before you begin work, mist the work area liberally, both air and surfaces. The goal isn't to get anything wet. Just the added humidity is enough to all but eliminate static electricity.

2.3.3 Removing and Replacing the Cover

It
sounds stupid, but it's not always immediately
obvious how to get the cover off the chassis. We've
worked on hundreds of different PCs from scores of manufacturers over
the years, and we're still sometimes stumped.
Manufacturers use an endless variety of fiendish ways to secure the
cover to the chassis. Some were intended to allow tool-free access,
others to prevent novice users from opening the case, and still
others were apparently designed just to prove there was yet one more
way to do it.

We've seen novice upgraders throw up their hands in
despair, figuring that if they couldn't even get the
case open they weren't destined to become PC
technicians. Nothing could be further from the truth. It just
sometimes takes a while to figure it out.

The most evil example we ever encountered was a mini-tower case that
had no screws visible except those that secured the power supply. The
cover appeared seamless and monolithic. The only clue was a 2-inch
piece of silver "warranty void if
removed" tape that wrapped from the top of the cover
to one side, making it clear that the separation point was there. We
tried everything we could think of to get that cover off. We pulled
gently on the front of the case, thinking that perhaps it would pop
off and reveal screws underneath. We pressed in gently on the side
panels, thinking that perhaps they were secured by a spring latch or
friction fit. Nothing worked.

Finally, we turned the thing upside down and examined the bottom. The
bottom of computer cases is almost always unfinished metal, but this
one was finished beige material that looked just like the other parts
of the cover. That seemed odd, so we examined the four rubber feet
closely. They had what appeared to be center inserts, so we pried
gently on one of these with our small screwdriver. Sure enough, it
popped off and revealed a concealed screw within the rubber foot.
Once we removed those four screws, the cover slid off easily, bottom
first.

The moral is that what one person can assemble, another person can
disassemble. It sometimes just takes determination, so keep trying.
Obviously, your first resort should be the system manual, but manuals
have a way of disappearing when you need them most. Fortunately, most
cases don't use such convoluted methods. Standard
systems generally use one of the following methods to secure the
cover to the chassis:

These use five screws (one per corner and
one at top center) that pass through the chassis and thread into
receptacles on the inside of the cover. Don't
confuse the screws that secure the power supply with those that
secure the cover. Cover screws are located along the edge, while
power supplies are normally secured by four screws in a square
pattern located at the upper- and mid-left side of the rear panel as
you are viewing it. On these systems, the cover comprises the top,
front, and sides of the case, and slightly overhangs the rear of the
chassis when installed properly. The lower edge of each side of the
cover usually has a channel that fits a rail built into the chassis.
Once you remove the screws, slide the cover a few inches toward the
front and then lift it off. To install the cover, place it in
position with a gap of a few inches between the back edge of the
cover and the rear panel. Make sure that the channels in the bottom
of each side panel are aligned with the chassis rail grooves and then
slide the cover toward the rear of the PC until it seats. When
installing or removing the cover be careful not to snag the top
center screw receptacle on any of the cables.

These use three or more screws on the back of the case, which go
through an overlapping lip on the cover and thread into the chassis
itself. The removable part of the cover comprises the top and sides.
To remove the cover, remove the screws from the back (make sure to
remove only the cover screws,

not the screws
that secure the power supply), slide the cover back an inch or two,
and then lift it clear. You may have to tilt the cover slightly by
lifting the rear to allow it to come clear of the chassis. To
reinstall the cover, place it over the chassis with a 1- or 2-inch
gap between the front edge of the cover and the rear of the front
panel, then slide the cover forward. There is a lip around the sides
and top of the cover that fits inside the front cover of the case.
Usually, the top will fit easily if you've put the
cover on correctly, but the sides may need to be pressed in before
they will fit. Also note that there may be a lip or other retaining
mechanism at the bottom edge of the cover which you may need to align
before the cover will seat properly. Replace the screws from the
back.

These generally use three or four screws
equally spaced down each side to secure the cover. The covers on most
of these system cases resemble those on recent AT-style and
low-profile cases. The front of the cover at the top and on both
sides has an underbeveled lip that slides under the rear edge of the
front bezel. The bottom edges of both side panels are channeled to
fit guides that protrude vertically from the bottom of the chassis on
each side. After removing the screws that secure it, remove the cover
by sliding it far enough to the rear to clear the lips at the top and
side front of the cover from the front panel bezel. Then lift it off.

Replacing the cover on one of these systems is often difficult
because you must guide the lips on the top and both side panels of
the cover under the front bezel while simultaneously making sure that
the bottom of each side panel seats in the guides. The easiest way to
do this is usually to lower the cover over the chassis a few inches
back from its ultimate seated position. Then lift the rear of the
cover an inch or two to angle the cover slightly. Make sure that the
bottom edges of the cover seat in their channels, and then slide the
cover toward the front while keeping the rear of the cover lifted an
inch or two. Guide the top lip of the cover under the front bezel and
then slowly lower the rear of the cover, making sure that the lips on
the side panels slide under the sides of the front bezel.

Some of the easiest cases to work on are
screwless, or nearly so. For example, one of our own favorites, the
Antec KS-288 (http://www.antec-inc.com), has only one
thumbscrew, centered at the top of the back panel. After this
thumbscrew is removed, the top panel slides off to the rear. That in
turn frees both side panels, which simply lift off. Reassembling the
case is just as easy because it uses craftily-designed triangular
slots that make it easy to align things before dropping them into
place. If properly designed, a tool-free case can be just as rigid as
one that uses screws. Be careful, though, about buying a cheap
tool-free case. We've seen some that are incredibly
flimsy.

In addition to these standard case types, you may run into one of the
following:

These cases are designed to allow quick
access to the inside of the PC by removing only the top portion of
the case, while the sides, front, and back remain fixed. These cases
divide the top down the middle from front to back. To open them, you
generally remove two or four screws, which may be located on the top
of the case or at the top center of the back of the case. Once you
remove these screws, the two parts of the top either swing up on
hinges or can be removed completely. Although never very popular with
PC vendors, clamshell cases are still made, and are sometimes
encountered on low-volume, custom-built systems.

On these cases, all parts of the
cover except the sides are semipermanently attached. Each side panel
is individually secured to the chassis using thumbscrews or screws
along the rear and/or bottom of the case. To remove a side panel,
loosen the screws securing it and slide the panel toward the rear
and/or bottom of the case, as necessary. The front and/or top of
these panels are often secured using a lip that slides under an
overhang on the top or rear panel. Depending on the case design, you
may have to lift the panel slightly away from the chassis before it
will slide clear. To reinstall the panel, reverse the process,
guiding the lip into its matching channel until the panel slides
easily back into the closed position and then reinsert the
screws.

2.3.4 Managing Internal Cables and Connectors

When you pop the cover of a PC, the first
thing you'll notice is cables all over the place.
These cables carry power and signals between various subsystems and
components of the PC. Making sure they're routed and
connected properly is no small part of working on PCs.

The cables used in PCs terminate in a variety of connectors. By
convention, every connector is considered either male or female. Many
male connectors, also called plugs, have
protruding pins, each of which maps to an individual wire in the
cable. The corresponding female connector, also called a
jack, has holes that match the pins on the
mating male connector. Matching male and female connectors are joined
to form the connection. Rather than using pins and holes, the
connectors used on some cables (for example, modular telephone cables
and 10BaseT Ethernet cables) use other methods to establish the
connection. The connector that terminates a cable may mate with a
connector on the end of another cable, or it may mate with a
connector that is permanently affixed to a device, such as a hard
disk or a circuit board. Such a permanently affixed connector is
called a socket, and may be male or female.

Some cables use individual wires joined to a connector. Only three
cables of this sort are common in PCsthose used to supply
power to the motherboard and drives, those that connect front-panel
LEDs and switches to the motherboard, and those that connect
audio-out on a CD-ROM drive to a sound card.

Most PC cables contain many individual wires packaged as a
ribbon cable, so called because individually
insulated conductors are arranged side by side in a flat array that
resembles a ribbon. Ribbon cables provide a way to organize the wires
required to connect devices such as drives and controllers whose
interfaces require many conductors. Ribbon cables are used primarily
for low-voltage signals, although they are also used to conduct
low-voltage/low-current power in some applications. Common ribbon
cables range in size from the 10-wire cables used to extend embedded
serial ports from the motherboard to the back panel, through 34-wire
floppy drive cables, to 40-wire and 80-wire IDE drive cables, to 50-,
68-, and 80-wire SCSI cables. Ribbon cables are normally used only
inside the case because their electrical characteristics cause them
to generate considerable RF emissions, which can interfere with
nearby electronic components.

System designers attempt to avoid two potential dangers with regard
to PC cables. Most important is to prevent connecting a cable to the
wrong device. For example, connecting a 12-volt power cable to a
device that expects only 5 volts might have a catastrophic result.
This goal is achieved by using unique connectors that physically
prevent the cable from connecting to a device not designed to receive
it. The second potential error is connecting the cable backward. Most
PC cables prevent this by using asymmetrical connectors that
physically fit only if oriented correctly, a process called
keying.

Two keying methods are commonly used for PC cables, either
individually or in conjunction. The first uses mating connectors
whose bodies connect only one way, and is used for all power cables
and some ribbon cables. The second, used for most ribbon cables,
blocks one or more holes on the female connector and leaves out the
corresponding pin on the male connector. Such a ribbon cable can be
installed only when oriented so that missing pins correspond to
blocked holes.

An ideal PC cable therefore uses unambiguous keyed connectors. You
can't connect these cables to the wrong thing
because the connector only fits the right thing; you
can't connect it backward because the connector only
fits the right way. Fortunately, most of the really dangerous cables
in PCsthe ones that could damage a component or the PC itself
if they were misconnectedare of this sort. Power cables for
disk drives and ATX motherboards, for example, fit only the correct
devices and cannot be connected backward.

Some PC cables, on the other hand, require careful attention. Their
connectors may physically fit a component that
they're not intended to connect to, and/or they may
not be keyed, which means you can easily connect them backward if
you're not paying attention. Connecting one of these
cables incorrectly usually won't damage anything,
but the system may not work properly, either. The cables that link
front panel switches and indicator LEDs to the motherboard are of
this variety. So are the power cables for old-style AT motherboards,
and connecting these incorrectly

can destroy the
motherboard.

2.3.4.1 Ribbon cable fundamentals

On first glance, ribbon cables appear to
be dead standard. They're nearly all light gray
nowadays, although you may encounter light blue, white, or rainbow
ribbon cables on older systems. All of them use a contrasting colored
stripe to indicate pin 1 (brown in the case of the rainbow cables).
They use only two types of connectors (described later in this
section), both of which are female and only one of which is commonly
used nowadays. For a ribbon cable with a given number of wires, it
might seem that the only distinguishing features are how long the
cable is and whether it has connectors for two devices or just one.
Problems may arise, however, if incompatible keying methods are used
on the two connectors that need to mate.

So-called "round" ribbon cables have recently become popular, particularly with makers that cater to gamers and other enthusiasts. A round ribbon cable is simply a standard cable that has been sliced longitudinally into smaller groups of wires. For example, a standard flat 40-wire IDE ribbon cable might be sliced into ten 4-wire segments, which are then bound with cable ties or otherwise secured into a more-or-less round package. The advantage to round ribbon cables is that they reduce clutter inside the case and improve airflow. The disadvantage is that doing this damages signal integrity on the individual wires because signal-bearing wires are put into closer proximity than intended. We recommend you avoid round ribbon cables, and replace any you find in any of your systems with flat ribbon cables. Note, however, that some round cables, such as Serial ATA cables, are designed to be round and do not need to be replaced.

Most ribbon cables use
header-pin connectors, shown in Figure 2-2. Header-pin connectors are used on cables for
hard drives, CD-ROM drives, tape drives, and similar components, as
well as for connecting embedded motherboard ports to external rear
panel jacks. The female header-pin connector on the cable has two
parallel rows of holes that mate to a matching array of pins on the
male connector on the motherboard or peripheral. On all but the
least-expensive drives and other peripherals, these pins are enclosed
in a plastic socket designed to accept the female connector. On
inexpensive motherboards and adapter cards, the male connector may be
just a naked set of pins. Even high-quality motherboards and adapter
cards often use naked pins for secondary connectors (such as serial
ports or feature connectors).

Figure 2-2. A ribbon cable with a header-pin connector

Some header-pin
connectors, male and female, are not keyed. Others use connector body
keying, pin/hole keying, or both. This diversity means that it is
quite possible to find that you cannot use a particular header-pin
cable for its intended purpose. For example, we recently installed a
disk drive and attempted to use the IDE cable supplied with the drive
to connect that drive to the secondary IDE header-pin connector on
the motherboard. The motherboard end of that cable was keyed by a
blocked hole, but the header-pin connector on the motherboard had all
pins present, which prevented the cable from seating. Fortunately,
the cable that came with the motherboard fit both the motherboard and
the drive connectors properly, allowing us to complete the
installation.

If you run into such a keying problem,
there are three possible
solutions:

The IDE and other header-pin cables that most computer stores sell
utilize connectors that use neither connector body nor pin/hole
keying. You can use one of these cables of the proper size to connect
any device, but the absence of all keying means that you must be
especially careful not to connect it backward.

If you don't have an unkeyed cable available, you
may be able to remove the key from the existing cable. Most keyed
cables use a small bit of plastic to block one of the holes. You may
be able to use a needle to pry the block out far enough that you can
extract it with your needlenose pliers. Alternatively, try pushing a
pin into the block at an angle, then bending the top of the pin over
and pulling both bent pin and block with your pliers. If the key is a
solid, integral part of the cable (which is rarely the case), you may
be able to use a heated needle or pin to melt the key out of the hole
far enough for the pin to seat.

Sometimes you have no choice. If the stores are closed, the only
cable you have uses pin/hole keying with a solid block that you
can't get out, and you must connect that cable to a
header-pin connector that has all pins present, you have to go with
what you have. You can use diagonal cutters to nip off the pin that
prevents you from connecting the cable. Obviously, this is drastic.
If you nip the wrong pin, you'll destroy the
motherboard or expansion card, or at least render that interface
unusable. Before you cut, see if you can swap cables within the PC to
come up with an unkeyed cable for the problem connector. If not, you
can sometimes bend the offending pin

slightly enough to allow the female
connector to partially seat. This may be good enough to use as a
temporary connection until you can replace the cable. If all else
fails and you need to cut the pin, before doing so align the keyed
female connector with the pin array and verify just which pin needs
to be cut. Also, check the manual for a detailed list of signal/pin
assignments on that interface. The pin you are about to remove should
be labeled No Connection or N/C in that list. Use the old
carpenter's maxim heremeasure twice and cut
once.

Connector and keying issues aside, the most common mishap with
header-pin connectors occurs when you install the cable offset by a
column or a row. The socketed male connectors used on most drives
make this impossible to do, but the male connectors used on most
motherboards and expansion cards are an unsocketed double row of
pins, making it very easy to install the connector with the pins and
holes misaligned. Working in a dark PC, it's very
easy to slide a connector onto a set of header pins and end up with
an unconnected pair of pins at one end and an unconnected pair of
holes at the other. It's just as easy to misalign
the connector the other way, and end up with an entire row of pins
and holes unconnected.

Card-edge
connectors


, also
called edge-card connectors, form a connection
by sliding the female cable connector onto a formed portion of a PC
circuit board which has contacts laid down on the circuit card itself
to serve as the male connector. Card-edge connectors were commonly
used to connect 5.25-inch floppy drives, floppy interface tape
drives, and old-style ST506/412 hard drives, but are seldom used
anymore because the physical and electrical connection they provide
is inferior to that provided by a header-pin connector.

Card-edge connectors should be keyed on the male (circuit board) side
by the presence of an off-center slot, and on the female (cable) side
by the presence of a matching insert in the connector body to prevent
the cable from being installed backward. However, many card-edge
connectors on cables do not have this keying insert, which makes it
easy to install the cable backward. Some male card-edge connectors do
not have the keying slot, which makes it impossible to connect a
properly keyed cable to them.

The only common problem with card-edge connectors arises when you
need to connect a keyed cable to a device that has no keying slot.
Male connectors without a keying slot sometimes have a prenotched
area on the circuit board that you can break away with your long-nose
pliers to allow the keyed cable to seat. If not, you may be able to
use your pliers to remove the keying insert from the cable connector.
If neither of these solutions is workable, the only solution is to
replace the cable with an unkeyed version.

2.3.4.2 Locating pin 1

If you
upgrade your system and it fails to boot or the new device
doesn't work, chances are you connected a ribbon
cable backward. This can't happen if all connectors
and cables are keyed, but nearly all systems have at least some
unkeyed connectors. The good news is that connecting ribbon cables
backwards almost never damages anything. We're
tempted to say "never" without
qualification, but there's a first time for
everything. If this happens to you, go back and verify the
connections for each cable. Better yet, verify them before you
restart the system.

One of the experienced PC technicians who reviewed the first edition of this book tells us that he has "burned up" more than one floppy disk drive by installing the cable with the pins offset. We have frequently installed FDD cables reversed, offset, and in any other combination you can imagine (it always seems easier to seat a cable by feel than it does to remove the drive and do it right) with no worse result than the system failing to boot. The FDD cable carries only signal-level voltages, so we're not sure how offsetting pins could damage a drive, but we'll certainly be more careful in the future.

To avoid connecting a ribbon cable
backward, locate pin 1 on each device and then make sure that pin 1
on one device connects to pin 1 on the other. This is sometimes
easier said than done. Nearly all ribbon cables use a colored stripe
to indicate pin 1, so there's little chance of
confusion there. However, not all devices label pin 1. Those that do
usually use a silk-screened numeral 1 on the circuit board itself. If
pin 1 is not labeled numerically, you can sometimes determine which
is pin 1 in one of the following ways:

Instead of a numeral, some
manufacturers print a small arrow or triangle to indicate pin 1.

The layout of some circuit boards
allows no space for a label near pin 1. On these boards, the
manufacturer may instead number the last pin. For example, rather
than labeling pin 1 on an IDE connector, the manufacturer may label
pin 40 on the other side of the connector.

If there is no indication of pin 1 on the
front of the board, turn it over (this is tough for an installed
motherboard) and examine the reverse side. Some manufacturers use
round solder connections for all pins other than 1, and a square
solder connection for pin 1.

If
all else fails, you can make an educated guess. Many disk drives
place pin 1 closest to the power supply connector. On a motherboard,
pin 1 is often the one closest to the memory or processor. We freely
admit that we use this method on occasion to avoid having to remove a
disk drive or motherboard to locate pin 1 with certainty.
We've never damaged a component using this
quick-and-dirty method, but we use it only for IDE drives, rear-panel
port connectors, and other cables that do not carry power.
Don't try this with SCSI, particularly differential
SCSI.

Once you locate an
unmarked or unclearly marked pin 1, use nail polish or some other
permanent means to mark it so that you won't have to
repeat the process the next time.

2.3.4.3 Power supply cables

PC power supply cables are fully described in Chapter 26.

2.3.5 Setting Jumpers and DIP switches

Jumpers and DIP switches are two methods
commonly used to set hardware options on PCs and peripherals.
Although they look different, jumpers and DIP switches perform the
same functionallowing you to make or break a single electrical
connection, which is used to configure one aspect of a component.
Jumper or switch settings may specify such things as the amount of
installed memory, the base address, IRQ, and DMA assigned to a
device, whether a particular function is enabled or disabled, and so
on.

Older PCs and expansion cards often contain dozens of these devices,
and use them to set most or all configuration options. Newer PCs
typically use fewer jumpers and DIP switches, and instead use the
BIOS setup program to configure components. In fact, many recent
motherboards (e.g., Intel Pentium 4 boards) have only one jumper. You
close this jumper when you first install the board to allow such
static options as the speed of the installed processor to be
configured, or to perform such infrequent actions as updating the
Flash BIOS. That jumper is then opened for routine operation.

More properly
called a jumper block, a
jumper is a small plastic block with embedded
metal contacts that may be used to bridge two pins to form an
electrical connection. When a jumper block bridges two pins, that
connection is called

on ,

closed ,

shorted , or

enabled . When the jumper block is removed, that
connection is called

off ,

open , or

disabled . The pins
themselves are also called a jumper, usually abbreviated

JPx , where

x is a number
that identifies the jumper.

Jumpers with more than two pins may be used to select among more than
two states. One common arrangement, shown in Figure 2-3, is a jumper that contains a row of three
pins, numbered 1, 2, and 3. You can select among three states by
shorting pins 1 and 2, or pins 2 and 3, or by removing the jumper
block entirely. Note that you cannot jumper pins 1 and 3 because a
jumper can be used to close only an adjacent pair of pins.

Figure 2-3. A typical PC jumper (bottom center) set to close pins 1 and 2

You can often use your fingers to install and remove isolated
jumpers, but needle-nose pliers are usually the best tool. However,
jumpers are sometimes clustered so tightly that even needlenose
pliers may be too large to grab just the jumper you want to work on.
When this happens, use your hemostat. When you open a jumper,
don't remove the jumper block entirely. Instead,
install it on just one pin. This leaves the connection open, but
ensures that a jumper block will be handy if you later need to close
that connection.

Jumper blocks come in at least two sizes that are not
interchangeable. Standard blocks are the largest and the most
commonly used, and are usually black. Mini jumper blocks are used on
some disk drives and boards that use surface-mount components, and
are often white or light blue. One of our technical reviewers reports
that Quantum uses still a third size, which we'll
deem "micro" jumper blocks, on some
of its drive models. He reports that these tiny blocks disappear when
dropped, cling like a burr to jumper pins, and are extremely hard to
work with, even when using fine tweezers. New components always come
with enough jumper blocks to configure them. If we remove one when
configuring a device, we usually tape it to a convenient flat area on
the device for possible future use. It's also a good
idea to keep a few spares on hand, just in case you need to
reconfigure a component from which someone has removed all the
"surplus" jumper blocks. Anytime
you discard a board or disk drive, strip the jumper blocks from it
first and store them in your parts tube.

A DIP switch, shown in Figure 2-4, is a small plastic block that contains one or
more (usually four or eight) individual slide or rocker switches.
Each of these individual switches performs the same function as a
jumper block. Turning an individual switch on is equivalent to
installing a jumper block, and turning it off to removing the jumper
block. DIP switches are labeled

SWx , where

x is a number that identifies the switch block.
Each individual switch within the block is also numbered.

Figure 2-4. DIP switch (3 and 5 off, others on)

The "on" position may be indicated
by the word

On ,

Close ,

Short , or

Enable printed on
one side of the switch, or by an arrow pointing to the on side. Turn
on a rocker switch by depressing the side of the switch or the raised
nub toward the on side. Turn on a slide switch by sliding the nub
toward the on side.

2.3.6 Installing and Removing Expansion Cards

Expansion cards
are circuit boards that you install in
a PC to provide functions that the PC motherboard itself does not
provide. For example, many motherboards don't
include video circuitry. PCs built with such motherboards use a
separate video adapter expansion card to provide such circuitry.
Internal modems, sound cards, network adapters, and disk controllers
are other commonly used expansion cards. Figure 2-5
shows a typical expansion card.

Figure 2-5. An expansion card

Each expansion card plugs into an expansion slot
located on the motherboard or on a riser card
that attaches to the motherboard. The rear panel of the PC chassis
includes a cutout for each expansion slot, which provides external
access to the card. The cutouts for vacant expansion slots are
covered by thin metal slot covers that are
secured to the chassis. These covers prevent dust from entering
through the cutout and also preserve the cooling airflow provided by
the power supply fan and any auxiliary fans installed in the
system.

To install an expansion card, remove the slot cover, which may be
secured by a small screw or may simply be die-stamped into the
surrounding metal. In the latter case, carefully twist off the slot
cover using a screwdriver or your needlenose pliers. If you need to
replace the slot cover later, secure it to the chassis using a small
screw that fits a notch in the top portion of the slot cover. The
back of the expansion card forms a bracket that resembles a slot
cover and is secured to the chassis in the same way. Depending on the
purpose of the card, this bracket may contain connectors that allow
you to connect external cables to the card.

Cheap cases sometimes have slot covers that must be twisted off to be removed and are destroyed in the process. If you need to cover an open slot in such a case and don't have a spare slot cover, ask your local computer store, which probably has a stack of them in its storeroom.

Installing and removing expansion cards
is by far the most common activity you'll perform
when working on PCs. Even if you are not working on a particular
expansion card, you must sometimes remove it to provide access to the
section of the PC that you do need to work on. Installing and
removing expansion cards may be hard or easy, depending on the
quality of the case, the motherboard, and the expansion card itself.
High-quality cases, motherboards, and expansion cards are built to
tight tolerances, making expansion cards easy to insert and remove.
Cheap cases, motherboards, and expansion cards have such loose
tolerances that you must sometimes literally bend sheet metal to
force them to fit.

People often ask whether it matters
which card goes into which slot. Beyond the obviousthere are
different kinds of expansion slots, and a card can be installed only
in a slot of the same typethere are four considerations that
determine the answer to this question:

Depending on the size of the card and the design of the motherboard
and case, a given card may not physically fit a particular slot. For
example, a protruding drive bay, memory module, or processor may
prevent a slot from accepting a full-length card. If this occurs, you
may have to juggle expansion cards, moving a shorter card from a
full-length slot to a short slot and then using the freed-up
full-length slot for the new expansion card. Also, even if a card
physically fits a particular slot, a connector protruding from that
card may interfere with another card, or there may not be enough room
to route a cable to it.

There are several variables, including slot type, card type, BIOS,
and operating system, that determine whether a card is
position-sensitive. We'll describe the different bus
and slot types in Chapter 3, but for now
it's enough to know that ISA cards are not
slot-sensitive, but EISA (Enhanced
Industry Standard Architecture) cards which are used in
older servers, as well as PCI cards may be. For this reason, although
it may not always be possible, it's good general
practice to reinstall a card into the same slot that you removed it
from.

Although interrupt conflicts are rare with PCI motherboards and modern operating systems, they can occur. In particular, PCI motherboards with more than four PCI slots share interrupts between slots, so installing two PCI cards that require the same resource in two PCI slots that share that interrupt may cause a conflict. If that occurs, you can eliminate the conflict by relocating one of the conflicting expansion cards to another slot. Even in a system with all PC slots occupied, we have frequently eliminated a conflict just by swapping the cards around. See your motherboard manual for details.

Although it is relatively uncommon nowadays, some combinations of
motherboard and power supply can provide adequate power for
power-hungry expansion cards such as internal modems only if those
cards are installed in the slots nearest the power supply. This was a
common problem years ago, when power supplies were less robust and
cards required more power than they do now, but you are unlikely to
experience this problem with modern equipment. One exception to this
is AGP video cards. Many recent motherboards support only AGP 2.0
1.5V and/or AGP 3.0 0.8V video cards, which means that older 3.3V AGP
cards are incompatible with that slot.

Another problem that is much less common with recent equipment is
that some expansion cards generate enough RF to interfere with cards
in adjacent slots. Years ago, the manuals for some cards (notably
some disk controllers, modems, and network adapters) described this
problem, and suggested that the card be installed as far as possible
from other cards. We haven't seen this sort of
warning on a new card in years, but you may still encounter it if
your system includes older cards.

2.3.6.1 Installing expansion cards

To install an expansion card, proceed as follows:

Remove the cover from the chassis and examine the motherboard to
determine which expansion slots are free. Locate a free expansion
slot of the type required by the expansion card (expansion slot types
are detailed in Chapter 3). Recent PCs may have
several types of expansion slots available, including ISA, PCI,
combination ISA/PCI, AGP, AMR, CNR, and ACR slots. Older PCs may have
other types of unused expansion slots, including VLB (VESA Local Bus,
an obsolete bus standard) and EISA. If more than one slot of the
proper type is free, you can reduce the likelihood of heat-related
problems by choosing one that maintains spacing between the expansion
cards rather than one that clusters the cards.

An access hole for each expansion slot is present on the rear of the
chassis. For unoccupied slots, this hole is blocked by a thin metal
slot cover secured by a screw that threads downward into the chassis.
Determine which slot cover corresponds to the slot you chose. This
may not be as simple as it sounds. Some types of expansion slots are
offset, and the slot cover that appears to line up with that slot may
not be the right one. You can verify which slot cover corresponds to
a slot by aligning the expansion card itself with the slot and seeing
which slot cover the card bracket matches to.

Remove the screw that secures the slot cover, slide the slot cover
out, and place it and the screw aside.

If an internal cable blocks access to the slot, gently move it aside
or disconnect it temporarily, noting the proper connections so that
you will know where to reconnect them.

Guide the expansion card gently into position, but do not yet seat
it. Verify visually that the tongue on the bottom of the expansion
card bracket will slide into the matching gap in the chassis and that
the expansion card bus connector section aligns properly with the
expansion slot. Figure 2-6 shows an expansion card
being fitted to the motherboard in a high-quality case, with the card
properly aligned and ready to be seated. Figure 2-7
shows the same card being installed in a cheap case, which
doesn't allow the card to align properly with the
slot if the card bracket is aligned with the chassis. With cheap
cases, you may have to use pliers to bend the card bracket slightly
to make the card, chassis, and slot all line up. Rather than doing
that, we prefer to replace the case.




Figure 2-6. An expansion card properly aligned and ready to seat





Figure 2-7. The same card in a cheap case, not aligning properly with the expansion slot




When you are sure that everything is properly aligned, position your
thumbs on the top edge of the card, with one thumb at each end of the
expansion slot below the card, and press gently straight down on the
top of the card until it seats in the slot. Apply pressure centered
on the expansion slot beneath the card, and avoid twisting or
torquing the card. Some cards seat easily with little tactile
feedback. Others require quite a bit of pressure and you can feel
them snap into place. Once you complete this step, the expansion card
bracket should align properly with the screw hole in the chassis.

Replace the screw that secures the expansion card bracket, and
replace any cables that you temporarily disconnected while installing
the card. Connect any external cables required by the new
carddon't tighten the thumbscrews quite
yetand give the system a quick once-over to make sure you
haven't forgotten to do anything.

Turn on the PC and verify that the new card is recognized and that it
functions as expected. Once you have done so, power the system down,
replace the cover, and reconnect everything. Store the unused slot
cover with your spares.

2.3.6.2 Removing expansion cards

To remove an expansion card, proceed as
follows:

Remove the system cover and locate the expansion card to be removed.
It's surprising how easy it is to remove the wrong
card if you're not careful. No wonder surgeons
occasionally get it wrong.

Once you're sure you've located the
right card, disconnect any external cables connected to it. If the
card has internal cables connected, disconnect those as well. You may
also need to disconnect or reroute other unrelated cables temporarily
to gain access to the card. If so, label those you disconnect.

Remove the screw that secures the card bracket, and place it safely
aside.

Grasp the card firmly near both ends and pull straight up with
moderate force. If the card will not release,


gently rock it from front to back (parallel to
the slot connector) to break the connection. Be careful when grasping
the card. Some cards have sharp solder points that can cut you badly
if you don't take precautions. If
there's no safe place to grasp the card and you
don't have a pair of heavy gloves handy, try using
heavy corrugated cardboard between the card and your skin.

If you plan to save the card, place it in an antistatic bag for
storage. If you are not installing a new expansion card in the
vacated slot, install a slot cover to ensure proper airflow and
replace the screw that secures the slot cover.

You may encounter an expansion card that's seated so tightly that it appears to be welded to the motherboard. When this happens, it's tempting to gain some leverage by pressing upward with your thumb on a connector on the back of the card bracket. Don't do it. The edges of the chassis against which the bracket seats may be razor-sharp, and you may cut yourself badly when the card finally gives. Instead, loop two pieces of cord around the card to the front and rear of the slot itself, and use them to "walk" the card out of its slot, as shown in Figure 2-8. Your shoelaces will work if nothing else is at hand. For a card that's well and truly stuck, you may need a second pair of hands to apply downward pressure on the motherboard itself to prevent it from flexing too much and possibly cracking as you pull the card from the slot.

Figure 2-8. Barbara pulling a recalcitrant expansion card the safe
way

2.3.7 Installing Drives

We attempted to write an overview section here to describe how to
install and configure drives. Unfortunately, we found it impossible
to condense that information to an overview level. Physical
installation procedures vary significantly, and configuration
procedures even more, depending on numerous factors, including:

Drive type

Physical drive size, both height and width

Internal (hard drives) versus externally accessible (floppy, optical,
and tape drives)

Mounting arrangements provided by the particular case

Drive interface (SCSI versus ATA/ATAPI)

For specific information about installing and configuring various
drive types, including illustrations and examples, refer to the
following chapters:

Floppy disk drives, Chapter 6

High-capacity floppy disk drives, Chapter 7

Tape drives, Chapter 9

CD-ROM drives, Chapter 10

DVD drives, Chapter 12

Hard disk drives, Chapter 14

Cases, Chapter 25

Building a PC, Chapter 28