mboard tshooting

28MOTHERBOARD

TROUBLESHOOTING

938

CONTENTS AT A GLANCE

Active, Passive, and Modular

Understanding the MotherboardSocket 7, Socket 8, or Slot 1AT, ATX, and NLXLearning your way around

Troubleshooting a MotherboardRepair vs. replaceStart with the basicsSymptoms

Further Study

The motherboard is the heart of any personal computer. It provides system resources (i.e.,IRQ lines, DMA channels, I/O locations), as well as “core” components, such as the CPU,chipset(s), Real-Time Clock (RTC), and all system memory—including RAM, BIOS ROM,and CMOS RAM. Indeed, most of a PC’s capabilities are defined by motherboard compo-nents. This chapter is intended to provide a guided tour of contemporary motherboards andshow you how to translate error information and symptoms into motherboard repairs.

Active, Passive, and ModularBefore going any further, you should understand the difference between a motherboardand a backplane. For the purposes of this book, a motherboard is a printed circuit boardthat contains most of the processing components required by the computer. PC purists of-

ten refer to a motherboard as an active backplane. The term active is used because ICs arerunning on the board. The advantage of a motherboard is its simplicity—the motherboardvirtually is the PC. Unfortunately, the motherboard has disadvantages. Namely, it is dif-ficult to upgrade. Aside from plugging in an upgraded CPU or adding RAM, the only realway to upgrade a motherboard is to replace it outright with a newer one. For example, theonly way to add PCI bus slots to an all-ISA motherboard is to replace the motherboardwith one that contains PCI slots.

On the other hand, a backplane (also referred to as a passive backplane) is little morethan a board containing interconnecting slots—no ICs are on the backplane (except per-haps some power-supply regulating circuitry). The CPU, DRAM, BIOS ROM, and othercentral-processing components are fabricated onto a board that simply plugs into one ofthe backplane slots. Other expansion devices (e.g., video board, drive controller, soundboard, etc.) just plug into adjacent slots. The PS/2 was one of the first PCs to use a back-plane design. Backplane systems are easy to troubleshoot. Unlike traditional mother-boards, which require the entire system to be disassembled, a processor board can beremoved and replaced as easily as any other board, so it is also a simple matter to upgradethe PC by installing a new processor board. The great limitation to backplanes is the bus.Where traditional motherboards can optimize a system with different busses, the back-plane is limited to a single bus style (usually ISA or MCA). High-performance bus archi-tectures, such as VL or PCI, are not readily available.

In an effort to provide a motherboard that is more upgradeable and serviceable, manufac-turers are experimenting with modular motherboards. The modular motherboard places theCPU, math co-processor, and key support ICs on a replaceable card that plugs into a moth-erboard. This, in turn, holds BIOS ROM, CMOS RAM, DRAM, other system controllers,and bus interfaces. The modular approach allows a motherboard to be upgraded far morethan a traditional motherboard, without having to replace it outright—the replacement pro-cessing card is then much cheaper than a new motherboard. However, today’s PC archi-tectures can usually support a variety of CPU versions and an extensive amount of RAM onthe original motherboard, so “modularity” has never become a very popular approach.

Contrary to popular belief, expansion bus connectors are not needed to make a mother-board. You can see this in any laptop or notebook computer motherboard (Fig. 28-1). Thedevices that traditionally demanded expansion slots (video and drive controllers) are eas-ily fabricated directly onto the motherboard. Even the motherboards used in most desktopand tower PCs over the last few years integrate video- and drive-controller circuits. If up-grades are needed in the future, the motherboard-based circuits can be disabled withjumpers, and replacement sub-systems are plugged into expansion slots.

Understanding the MotherboardBefore you can troubleshoot a motherboard effectively, it is important that you know yourway around and be able to identify at least most of the available components. Althougheach motherboard is designed differently, this process of identification is not nearly as dif-ficult as it might sound. This part of the chapter will familiarize you with the essentialfunctions and components that you’ll find on a modern motherboard.

UNDERSTANDING THE MOTHERBOARD 939

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SOCKET 7, SOCKET 8, OR SLOT 1

When examining a motherboard, you’ll probably find it designated as “Socket 7,”“Socket 8,” or “Slot 1.” These classifications refer to the type of CPU that the mother-board can support: Socket-7 motherboards are generally designed for Pentium and Pen-tium MMX CPUs, Socket-8 motherboards are made for PentiumPro CPUs, and Slot-1motherboards are slated for Pentium II systems. This does not mean that a mother-board can support ANY such processor, only that the motherboard supports a given“class” of processor. For example, older Pentium motherboards can only support Pen-tium CPUs up to 120MHz, but newer Pentium motherboards can support Pentium (orPentium MMX) processors up to 200MHz—but all would be categorized as “Socket 7”motherboards. You can find a complete breakdown of socket/slot designations inChapter 11.

940 MOTHERBOARD TROUBLESHOOTING

BIOS ROM(IC19)

UART/Parallel(IC27)

Regulator(IC45)

dc-dc converter(IC43)

EMS control(IC20)

FDC(IC39)

VRAM(IC33,34)

LCDC(IC35)

Keyboardcontroller(IC21)

DRAM (256K-bit)(IC16, 18)

DRAM (256K-bit)(IC15, 17)

DRAM (1M-bit)(IC11-14)

Comparator(IC42)

CPU/systemcontrol

(IC2)

CPU(V20)(IC1)

EEPROM(IC31)

EMS memory (SIMM)socket (CN1)

FIGURE 28-1 Motherboard assembly for a Tandy 1500HD laptop. Tandy Corporation

AT, ATX, AND NLX

Another important classification that you must be familiar with is the motherboard’s formfactor. In simplest terms, the form factor is little more than the dimensions of the boardand its mounting-hole positions, as well as the general layout and placement of key com-ponents such as the CPU, SIMMs, and expansion slots. Today, the three major form fac-tors to consider are: AT, ATX, and NLX. It is important for you to understand that formfactors do not directly influence performance—a “baby AT” motherboard and an NLXmotherboard can offer exactly the same performance characteristics. Form factor is mostimportant in system assembly and access for service.

AT-style motherboards The “AT-style” motherboards really represent the classic ap-proach to component placement (Fig. 28-2). AT-style motherboards are typically avail-able in two variations: the “Baby AT” and the “Full AT.” Both variations simply affectthe overall dimensions of the motherboard (Full AT motherboards are larger). You canusually identify an AT-style motherboard based upon two distinctions. First, look at thepower connectors where the power supply attaches. An AT-style motherboard uses twosets of 6-pin in-line connectors. Second, the CPU is usually positioned in line with theISA bus slots (almost always obstructing full-length ISA cards).

ATX-style motherboards “ATX-style” motherboards are the result of the first seri-ous industry push to “standardize” the dimensions and connections of a PC motherboard,such as the ATX Slot 1 motherboard (Fig. 28-3). An ATX motherboard is distinguishedby three points. First, all I/O port connectors are concentrated into a single “I/O panel” atthe rear of the motherboard. Second, the ATX motherboard uses a 20-pin PS/2-stylepower connection from the power supply. Third, the CPU is located clear and away fromall expansion bus slots—eliminating any interference with full-slot expansion cards. ATXmotherboards can be found supporting Socket 7, Socket 8, and Slot 1 CPUs.

NLX-style motherboards Although ATX motherboards represented a good effort atstandardization, they still retain all the assembly problems of AT-style motherboards—namely that the motherboard is cumbersome to install and time-consuming to upgrade orreplace. The “NLX-style” motherboards (Fig. 28-4) overcome this disadvantage by mak-ing the motherboard a replaceable “card,” and moving all expansion slots and connectionheaders (e.g., speaker connector, power-switch connector, etc.) to a “riser card.” The NLXmotherboard itself then plugs into the riser card. In this fashion, the motherboard canquickly and easily be removed from the system to change jumpers, add memory, or installa replacement motherboard.

LEARNING YOUR WAY AROUND

Now that you’ve seen some essential motherboard classifications, it’s time to actually lookat a motherboard up close, and identify the crucial parts. For the purposes of this book, the


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The Socket-5 connector shown in Fig. 34-2 indicates an i486 motherboard.


Megatrends

Megatrends

Meg

atre

nd

s

FIGURE 28-2 The AMI Atlas PCI motherboard. American Megatrends, Inc.


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Megatrends

PCI slots ATX I/Oconnectors

Slot 1 CPUconnector

SIMM/DIMMslots

ISA slots

FIGURE 28-3 An Intel ATX Slot 1 motherboard. Intel Corporation

NLX I/Oconnectors

NLX card edgeconnector

Slot 1 CPUconnector

SIMM/DIMMslots

FIGURE 28-4 An Intel NLX Slot 1 motherboard. Intel Corporation

Intel PD440FX ATX Slot 1 motherboard (Fig. 28-5) is used as a model. Other mother-boards and form factors will appear a bit different, but the basic key parts are all the same.The pinouts of each major connector are illustrated in Fig. 28-6.

1 ISA bus slots For ISA adapter boards.2 Yamaha OPL4-ML This optional on-board wavetable synthesizer features the single-

chip OPL4-ML (YMF704) IC. The OPL4-ML integrates the OPL3 audio system, gen-eral MIDI processor, and wavetable ROM into a single component. The featuresinclude: general MIDI system-1 compliance, an interface compatible with MPU-401UART mode, FM synthesis that is compatible with the OPL3 audio system, andwavetable synthesis generates up to 24 voices simultaneously.

3 Yamaha OPL3-SA3 This optional on-board audio subsystem features the Yamaha OPL3-SA3 (YMF715) IC. The features include: a 16-bit audio CODEC and OPL3 FM synthe-sis; an integrated 3-D enhanced stereo controller including all required analog components;an interface for MPU-401 and a joystick (game port); stereo analog-to-digital and digital-


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29

28

27

26

10

11

12

13

14

15

25 24 23 22 21 20 19 18 17 16

1 2 3 4 5 6 7 8 9

FIGURE 28-5 An Intel PD440FX motherboard layout. Intel Corporation

The following chipset components are presented for example purposes only. Your moth-erboard will undoubtedly use different chips (and chipsets)—each offering their own setof characteristics.

to-analog converters; analog mixing, anti-aliasing, and reconstruction filters for sound re-production; line, microphone, and monaural inputs; ADPCM, A-law, or M-law digital au-dio compression and decompression; full digital control of all mixer and volume-controlfunctions; software switching between rear-panel mic-in and line-in connectors; Plug-and-Play compatibility; and Sound Blaster Pro and Windows Sound System compatibility.

4 CD-ROM audio connector This is necessary to play CD audio through the mother-board’s sound system (used in conjunction with on-board sound). It is a 4-pin headerand the pinout is shown in Table 28-1.

5 Telephony connector Telephony support is available on some motherboards for connect-ing the monaural audio signals of an “internal telephony device” to the motherboard’saudio subsystem. A monaural audio-in and audio-out signal interface is necessary for


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TelephonyJ2F1

11

2

20

PCIconnectors(4)

J4C1, J4D1J4E1, J4E2

ISAconnectors(3)

J4A1, J4B1 J4B2J4F1

J6C1

J7C1

J9D1

Front panel I/O connectors

GP I/O

J7D1

J9A1

J8H3J10H1

J6F1

34

Fan 1

Fan 3

1 2

1 2

1

1

Chassissecurity

Yamahawavetable

module

Yamahawavetable

module

1

1

2

SecPri

27

1

84

1

1

7

103

3

Hard disk LED(HDD LED)

J8H1

Bank 0 DRAM(J6J1, J6J2)

Slot 1processorcard connectorJ4A1

Bank 1 DRAM(J7J1, J7J2)

J8H2

1

8

1

2

5 Floppy

PCI IDE(2)

331

1 39

20

2

1 3

J6M1

WavetableJ2F3

Telephony

41J1F1

Line in

41J2F6

CD-ROM audio

J2F2

Power

FIGURE 28-6 Connector pinouts of an Intel PD440FX motherboard. Intel

Corporation

telephony applications, such as speakerphones, fax/modems, and answering machines.Two different interface headers are available for this application: a general telephonyinterface with a 1- × 4-pin ATAPI-type connector (Table 28-2), and a telephony inter-face with a 2- × 2-pin header (same function as #7).

6 Wavetable header This 2- × 4-pin header supports wavetable add-in cards. Mostwavetable add-in cards are installed in an ISA slot, and a cable is routed from the cardto this header. Compatible wavetable cards include the ICS WaveFront and the Crysta-Lake Series 2000 wavetable product.

8 Line-in connector The line-in connector is available for connecting left and right chan-nel signals of an internal audio device to the motherboard’s audio subsystem. An au-dio-in signal interface of this type is necessary for such applications as TV tuner boards.A general audio interface is provided with a 1- × 4-pin ATAPI-type connector (Table28-4).

9 Back-panel I/O connectors These are the group of I/O connectors that reside on theback panel. These include serial ports, parallel ports, USB ports, keyboard and mouse


TABLE 28-1 CD-ROM AUDIO CONNECTOR PINOUT

PIN SIGNAL NAME

1 Ground

2 CD Left

3 Ground

4 CD Right

TABLE 28-2 TELEPHONY CONNECTORPINOUTS

1X4 ATAPI CONNECTOR

PIN SIGNAL NAME

1 MONO IN (from external device)

2 Ground

3 Ground

4 MONO OUT (to external device)

2X2 CONNECTOR

PIN SIGNAL NAME

1 Ground

2 MONO IN (from external device)

3 MONO OUT (to external device)

4 Key

10 ports, game/MIDI ports, and sound connections. Figure 28-7 illustrates a typical ATXback panel.

10 Slot-1 processor connector The processor connects to the motherboard through theSlot-1 processor connector, a 242-pin edge connector. When the processor is mountedin Slot 1, it is secured by a “retention mechanism” attached to the motherboard. Theprocessor’s heatsink is stabilized by a heatsink support that is attached to the mother-board.

11 Intel SB82442FX Data Bus Xccelerator (DBX) This is part of 440FX chipset, which con-trols the memory operations of the motherboard. The DBX connects to 64-bit processordata bus, the 64- or 72-bit memory data bus, and the 16-bit PMC chip’s private-data bus.The DBX works in parallel with the PMC chip to provide a high-performance memorysubsystem.

12 Intel SB82441FX PCI Bridge and Memory Controller (PMC) This is part of440FX chipset. The PMC chip provides bus-control signals and address paths for


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TABLE 28-3 WAVETABLE CONNECTOR PINOUT

PIN SIGNAL NAME PIN SIGNAL NAME

1 Wave In Right 2 Ground

3 Wave In Left 4 Ground

5 Key 6 Ground

7 Not connected 8 MIDI Out (from host)

TABLE 28-4 LINE IN CONNECTORPINOUT

PIN SIGNAL NAME

1 Left Line In

2 Ground

3 Ground

4 Right Line In (monaural)

Keyboard Parallel port MIDI/game portUSB 1

USB 0Mouse Serial

port 1Serialport 2

Line out Mic inLine in

FIGURE 28-7 Connector layout of a typical ATX back panel.

data transfers between the host bus, PCI bus, and main memory. The 82441FX pro-vides the following features:■ Microprocessor interface control, including processor host bus speeds up to 66

MHz and 32-bit addressing.■ An integrated DRAM controller providing a 64- or 72-bit non-interleaved path to

memory with ECC support, support for EDO DRAM, and support for 8MB to256MB of main memory.

■ A fully synchronous PCI bus interface that is compliant with the PCI specificationrevision 2.1 and operating at 33MHz PCI-bus speed for PCI-to-DRAM speedgreater than 100MB/sec.

13 Power connector This is a 20-pin PS/2-type power connector that supplies +5, -5,+12, -12, and +3.3 V to the ATX motherboard. Table 28-5 lists the pinout for thispower connector.

14 Speaker This is a small integrated general-purpose speaker. Some motherboardsmight replace an integrated speaker with a 2-pin header for an external speaker in thecase.

15 Battery The CMOS RAM backup battery.16 SIMM sockets The sockets for 72-pin SIMMs—later motherboards use 168-pin

DIMMs.17 IDE connectors The 40-pin primary and secondary drive-controller channels for ATA

(IDE), ATA-2 (EIDE), and ATAPI devices (such as CD-ROM drives).18 GP I/O header A general-purpose I/O connector. Table 28-6 lists the pinout for a GP

I/O connector.19 Floppy-drive connector The 28-pin floppy-drive channel.20 Intel SB82371SB PCI/ISA IDE Xccelerator (PIIX3)21 Front-panel header The group of connectors used to connect front-panel switches and

indicators, such as the speaker, reset switch, power LED, hard-drive activity LED(HDD LED—same as #20), infrared (IrDA) port, sleep switch, or power switch. Fig-ure 28-8 shows a typical header arrangement for an ATX motherboard. Table 28-7lists the pinout the header connectors.

22 TSOP flash device The BIOS ROM IC.


TABLE 28-5 ATX POWER CONNECTOR PINOUT

CONNECTOR SIGNAL NAME CONNECTOR SIGNAL NAME

1 +3.3 V 11 +3.3 V

2 +3.3 V 12 –12 V

3 Ground 13 Ground

4 +5 V 14 PW_ON#

5 Ground 15 Ground

6 +5 V 16 Ground

7 Ground 17 Ground

8 PWRGD (power good) 18 –5 V

9 +5 VSB (standby for real-time clock) 19 +5 V

10 +12 V 20 +5 V


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TABLE 28-6 GP I/O CONNECTORPINOUT

PIN SIGNAL NAME

1 Vcc

2 Key

3 GP1 7

4 Ground

5 GP1 2

6 Ground

7 GP1 1

8 Ground

Speaker Reset Pwr LED HD LED Infrared Sleep Pwr on

27 1

FIGURE 28-8 Front-panel header layout for a typical ATX motherboard.

TABLE 28-7 FRONT PANEL HEADER ASSIGNMENTS

PIN SIGNAL NAME

1 SW_ON# (power-on connector)

2 Ground

3 SLEEP (sleep/resume switch)

4 Sleep Pullup (SLEEP_PU)

5 No connect

6 +5 V (IrDA connector)

7 Key

8 IrRX

9 Ground

10 IrTX

11 Consumer IR (CONIR)

12 No connect

13 HD_PWR +5 V (HDD LED connector)

14 Key

15 HD Active#

16 HD_PWR

17 No connect

18 Ground (sleep/power LED)

19 Key

20 PWR_LED

21 No connect

22 G d (R t it h)

23 Configuration jumper block The group of jumpers used to configure the motherboard.Typical configuration jumpers can include (but are not limited to):■ Bus speed One or more jumpers used to set the motherboard bus speed.■ Clock multiplier One or more jumpers used to multiply the bus speed for the given

CPU.■ CPU type One or more jumpers used to define the presence of an Intel, AMD, or

Cyrix CPU.■ CPU voltage(s) One or more jumpers used to select the particular operating volt-

age(s) for a given CPU.■ Video port If the motherboard offers on-board video, this jumper enables or dis-

ables it.■ Hard drives If the motherboard offers on-board hard-drive ports, this jumper en-

ables or disables it.■ Floppy drives If the motherboard offers an on-board floppy-drive port, this jumper

enables or disables it.■ CMOS clear This jumper can be used to clear the CMOS (NVRAM and ESCD).■ Clear password This jumper can be used to erase the CMOS password(s) without

clearing the CMOS.■ CMOS access This jumper can be used to prevent access to the CMOS setup rou-

tine.■ BIOS recovery This jumper can be used to invoke BIOS boot block recovery if a

BIOS flash upgrade fails.24 National PC87307VUL I/O controller The PC87307 super I/O controller from Na-

tional Semiconductor is an ISA Plug-and-Play compatible, multifunction I/O devicethat provides the following features:■ Two serial ports Including two 16450/16550A-software compatible UARTs, an in-

ternal send/receive 16-byte FIFO buffer, and four internal 8-bit DMA options forthe UART with SIR support (USI).

■ A multimode bi-directional parallel port that can operate in Standard mode (IBMand Centronics compatible), Enhanced Parallel Port (EPP) mode with BIOS anddriver support, or high-speed Extended Capabilities Port (ECP) mode.

■ A floppy-disk controller that is DP8473 and N82077 compatible.■ A keyboard and mouse controller that is industry-standard 8042A compatible.■ A real-time clock that is DS1287 and MC146818 compatible, and is accurate

within ±13 minutes/year at 25°C with 5 V applied.


TABLE 28-7 FRONT PANEL HEADER ASSIGNMENTS (CONTINUED)

22 Ground (Reset switch)

23 SW_RST

24 Ground (Speaker)

25 Key

26 PIEZO_IN

27 SPKR_HDR

PIN SIGNAL NAME

■ Support for Advanced Power Control (APC).■ Support for an IrDA and consumer IR-compliant infrared interface.

25 Fan 1 header A connector used to power a fan in the system and detect its operation(same function as #30). Pin 1 is ground, pin 2 is +12 V, and pin 3 is a “fan sense” line,which can be monitored by the management-extension hardware (#29).

26 Yamaha wavetable module headers Two optional 2- × 3-pin connections are used forYamaha wavetable cards (Table 28-8). These connectors are not identical, and the oneyou use will depend on the particular wavetable card installed.

27 Chassis security header A “tamper” switch contact used in conjunction with man-agement-extension hardware (#29).

28 Management-extension hardware This optional management-extension hardwareprovides low-cost instrumentation capabilities that are designed to reduce the totalcost of owning a PC. The hardware implementation is a single-chip ASIC, which in-cludes such features as: an integrated temperature sensor, fan speed sensors for up tothree fans, power-supply voltage monitoring to detect levels above or below accept-able values, and a header for an external chassis-security switch feature.

29 PCI connectors For PCI adapter boards.

Troubleshooting a MotherboardBecause motherboards contain the majority of system processing components, it is likelythat you will encounter a faulty motherboard sooner or later. The BIOS POST is writtento test each sub-section of the motherboard each time the PC is powered up, so most prob-lems are detected well before you ever see the DOS prompt. Errors are reported in a myr-iad of ways. Beep codes and POST codes (Chapter 19) provide indications of fatal errorsthat occur before the video system is initialized. Still, plenty of symptoms can elude theinitial testing at start time. This part of the chapter digs in and presents a lengthy selectionof motherboard symptoms for you to reference.

REPAIR VS. REPLACE

This is the perennial troubleshooting dilemma. The problem with motherboard repair isnot so much the availability of replacement parts (although that can be a challenge) as is

TROUBLESHOOTING A MOTHERBOARD 951

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TABLE 28-8 YAMAHA WAVETABLE MODULECONNECTOR PINOUTS

PIN SIGNAL NAME PIN SIGNAL NAME

1 EXTEN# 1 RSTDRV

2 SIN 2 VCC

3 VCC 3 AUD33MHZ

4 Ground 4 MIDI Out

5 BCK 5 Ground

6 LACK 6 Key

the use of surface-mount soldering (SMT). You see, a surface-mounted IC cannot bedesoldered with conventional tools. To successfully desolder a surface-mounted IC, youneed to heat each of the IC’s pins (often in excess of 100) simultaneously, then lift the ICoff the board. It is then a simple matter to clean up any residual solder. Unfortunately,specialized surface-mount soldering equipment is required to do this. The equipment isreadily available commercially, so it is easy to buy—but you can invest $1000 to $2000 toequip your work bench properly.

As you can imagine, the “repair vs. replace” decision is an economic one. It makes lit-tle sense for the part-time PC enthusiast to make such a substantial investment to exchangea defective IC (which are usually under $30). It is generally better to replace the mother-board outright, which is only a fraction of the cost of such SMT equipment. On the otherhand, professionals who intend to pursue PC repair as a living are well served with sur-face-mount equipment. The customer’s cost for labor, the part(s), and markup is typicallymuch less than purchasing a new motherboard (especially the high-end boards such asi486/66 and Pentium motherboards).

START WITH THE BASICS

Because motherboard troubleshooting represents a significant expense, be sure to start anymotherboard repair by inspecting the following points in the PC. Remember to turn allpower off before performing these inspections:

■ Check all connectors This can happen easily when the PC is serviced or upgraded, andyou accidentally forget to replace every cable (or the cable is installed incorrectly).Start with the power connector, and inspect each cable and connector attached to themotherboard. Frayed cables should be replaced. Loose or detached cables should bereattached properly.

■ Check all socket-mounted ICs Some ICs in the computer (especially the CPU) get hotduring normal operation. It is not unheard of for the repetitive expansion and contrac-tion encountered with everyday use to eventually “rock” an IC out of its socket. TheCPU, math-co-processor (on older motherboards), BIOS ROM, and often the CMOS/RTC module are socket mounted, so check them carefully.

■ Check power levels Low or erratic ac power levels can cause problems in the PC. Usea multimeter and check ac at the wall outlet. Be very careful whenever dealing with ac.Take all precautions to protect yourself from injury. If the ac is low or is heavily loadedby motors, coffee pots, or other highly inductive loads, try the PC in another outlet run-ning from a different circuit. If ac checks properly, use your multimeter (or a measure-ment tool, such as PC Power Check from Data Depot) to check the power supplyoutputs. If one or more outputs is low or absent, you should repair or replace the supply.

■ Check the motherboard for foreign objects A screw, paper clip, or free strand of wirecan cause a short circuit that might disable the motherboard. Examine the motherboardcarefully and use ample lighting.

■ Check that all motherboard DIP switches and jumpers are correct For example, if themotherboard provides a video port and you have a video board plugged into the expan-sion bus, the motherboard’s video circuit will have to be disabled through a switch orjumper. Otherwise, a hardware conflict can result that might interfere with mother-


board operation. You will need the user manual for the PC to identify and check eachjumper or switch.

■ Check for intermittent connections and accidental grounding Inspect each of the moth-erboard’s mounting screws, and see that they are not touching nearby printed traces. Alsocheck the space under the motherboard and see that nothing that is grounding the mother-board and chassis. As an experiment, you might try loosening the motherboard mountingscrews. If the fault goes away, the motherboard might be suffering from an intermittentconnection—when all screws are tight, the board is bent just enough to let the intermittentappear. Unfortunately, intermittent connections are almost impossible to find.

SYMPTOMS

Symptom 28-1. A motherboard failure is reported, but goes away whenthe PC’s outer cover is removed An intermittent connection is on the motherboard.When the housing is secured, the PC chassis warps just slightly—this might be enough toprecipitate an intermittent contact. When the housing is removed, the chassis relaxes andhides the intermittent connection. Replace the outer cover and gently re-tighten each screwwith the system running. Chances are that you will find one screw that triggers the problem.You can leave that screw out, but it is advisable to replace the motherboard as a long-term fix.

Symptom 28-2. The POST (or your software diagnostic) reports a CPUfault This is a fatal error, and chances are that system initialization has halted. CPUproblems are generally reported when one or more CPU registers do not respond as ex-pected, or has trouble switching to the protected mode. In either case, the CPU is proba-bly at fault. Fortunately, the CPU is socket mounted and should be very straightforwardto replace. Be sure to remove all power to the PC and make careful use of static controlswhen replacing a CPU. Mark the questionable CPU with indelible ink before replacing it.

Zero-Insertion Force (ZIF) sockets are easiest because the IC will be released simply bylifting the metal lever at the socket’s side. Slide out the original CPU and insert a new one.Secure the metal lever and try the PC again. However, many CPUs are mounted in Pin-Grid Array (PGA) sockets, and a specialized PGA-removal tool is strongly suggested forproper removal. You should also be able to use a small, regular screwdriver to gently pryup each of the four sides of the CPU, but be very careful to avoid cracking the IC, thesocket, or the motherboard—never use excessive force. If the IC is free, install the newCPU with close attention to pin alignment, then gently press the new CPU into place.

A word about heatsink/fans. Most i486 (and later) CPUs are equipped with a metalheatsink (or heatsink/fan) assembly. It is vital to the proper operation of your system thatthe heatsink be re-installed correctly. Otherwise, the new CPU will eventually overheatand lock up or fail. Be sure to use good-quality thermal compound to ensure proper heattransfer to the heatsink (remember that a sound mechanical connection does not guaranteea good thermal connection).

Symptom 28-3. The POST (or your software diagnostic) reports a problemwith the floating-point unit Math co-processor (also called the Floating-Point Unit,FPU) problems are generally reported when one or more MPC registers do not respond asexpected. Fortunately, MCP faults are not always fatal. It is often possible to remove the


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MCP or disable the MCP availability through the CMOS setup. Of course, programs thatdepend on the MCP will no longer run, but at least the system can be used until a new oneis installed. On older systems that use separate MCPs, the device is socket mounted, andshould be very straightforward to replace. Be sure to remove all power to the PC, andmake careful use of static controls when replacing an MPC. Mark the questionable MPCwith indelible ink before replacing it. If the MCP is integrated into the CPU (i386DX,i486DX, Pentium, and later CPUs) are a bit more expensive because you’ll need to replacethe entire CPU, but the replacement process is no more difficult (remember to remount anyheatsink/fan assembly properly).

Symptom 28-4. The POST (or your software diagnostic) reports a BIOSROM checksum error The integrity of your system BIOS ROM is verified after theCPU is tested. This is necessary to ensure that no unwanted instructions or data could eas-ily crash the system during POST or normal operation. A checksum is performed on theROM contents, and that value is compared with the value stored in the ROM itself. If thetwo values are equal, the ROM is considered good and initialization continues. Otherwise,the BIOS is considered defective and should be replaced. Chapter 6 provides an index ofmajor BIOS manufacturers.

Traditionally, BIOS ROM is implemented as one or two ICs that are plugged into DIPsockets. They can be removed easily with the blade of a regular screwdriver, as long asyou pry the IC up slowly and gently (be sure to pry the IC evenly from both ends). Wheninstalling new DIP ICs, you might have to straighten their pins against the surface of atable or use a DIP pin-straightening tool. Ultimately, the IC pins will fit nicely into eachreceptacle in the DIP socket. You can then ease the IC evenly into the socket. Alignmentis crucial to ensure that all pins are inserted. If not, one or more pins might be bent underthe IC and ruin the new ROM. Also, be sure to insert the new IC(s) in the proper orienta-tion. If they are accidentally installed backward, they might be damaged.

Newer BIOS ICs use flash EEPROM technology, which allows the device to be erasedand reprogrammed in the field without having to replace the entire BIOS ROM IC. Whena flash BIOS fails its checksum test, it also has probably failed. Because flash BIOS de-vices are often fabricated as PLCC ICs, it is a bit easier to replace them, but you will needa PLCC-removal tool to take the original IC out of its socket—there simply is not enoughroom for a screwdriver.

Symptom 28-5. The POST (or software diagnostic) reports a timer (PIT)failure, an RTC update problem, or a refresh failure The PIT is often an 8254or compatible device. Ultimately, one or more of its three channels might have failed andthe PIT should be replaced. It is important to realize that many modern motherboards in-corporate the PIT functions into a system controller or other chipset IC (refer to Chapter 8for a listing of chipsets and functions). Because the PIT is typically surface mounted, youcan attempt to replace the device or replace the motherboard entirely.

Symptom 28-6. The POST (or software diagnostic) reports an interrupt con-troller (PIC) failure The PIC is often an 8259 or compatible device, and two PICs are onthe typical AT motherboard (PIC#1 handles IRQ0 through IRQ7, and PIC#2 handles IRQ8through IRQ15). Of the two, PIC#1 is more important because the lower interrupts have ahigher priority, and the lowest channels handle crucial low-level functions, such as the sys-


tem timer and keyboard interface. Generally, a diagnostic will reveal which of the two PICshave failed. Be sure that no interrupt conflicts are between two or more system devices.You can then replace the defective PIC. In many current systems, both PICs are integratedinto a system controller or chipset IC. You can replace the defective IC if you have the ap-propriate surface-mount equipment available, or replace the motherboard entirely.

Symptom 28-7. The POST (or software diagnostic) reports a DMA con-troller (DMAC) failure The DMAC is often an 8237 or compatible device, and twoDMACs are on the typical AT motherboard (DMAC#1 handles channel 0 through channel3 and DMAC#2 handles channel 4 through channel 7). Of the two, DMAC#1 is more im-portant because channel 2 runs the floppy-disk controller. Generally, a diagnostic will re-veal which of the two DMACs have failed. Be sure that no DMA conflicts are betweentwo or more system devices. You can then replace the defective DMAC. In many currentsystems, both DMACs are integrated into a system controller or chipset IC. You can re-place the defective IC if you have the appropriate surface-mount equipment available, orreplace the motherboard entirely.

Symptom 28-8. The POST (or software diagnostic) reports a KBC fault TheKeyBoard controller (KBC) is often either an 8042 or an 8742. Because the KBC is a mi-crocontroller in its own right, diagnostics can usually detect a KBC fault with great accu-racy. The KBC might either be a socket-mounted PLCC device, or (in rare cases) asurface-mounted IC. Remember, remove all power and mark the old KBC before you re-move it from the PC. You will probably need a PLCC-removal tool to take out the oldKBC. If you cannot exchange a defective KBC, you’ll need to replace the motherboard.

Symptom 28-9. A keyboard error is reported, but a new keyboard has noeffect The keyboard fuse on the motherboard might have failed. Many motherboard de-signs incorporate a small fuse (called a pico-fuse) in the +5-Vdc line that drives the key-board. If this fuse fails, the keyboard will be dead. Use your multimeter and measure the+5-Vdc line at the keyboard connector. If this reads 0 Vdc, locate the keyboard fuse on themotherboard and replace it (you might have to trace the line back to the fuse, which looksalmost exactly like a resistor).

Symptom 28-10. The POST (or software diagnostic) reports a CMOS orRTC fault With either error, the same device is usually at fault. The CMOS RAM and RTCare generally fabricated onto the sane device. RTC problems indicate that the real-time clockportion of the IC has failed or is not being updated. CMOS RAM failure can be caused by adead backup battery or by the failure of the IC itself. When dealing with a CMOS or setupproblem, try the following protocol. First, try a new backup battery and reload the CMOSsetup variables. If a new battery does not resolve the problem, the CMOS/RTC IC should bereplaced. Often, the CMOS/RTC IC is surface mounted, and will have to be replaced (or themotherboard will have to be replaced). However, the growing trend is toward making the ICsocket mounted and including the battery into a single replaceable module (such as the Dal-las Semiconductor-type devices). Modules are typically replaceable DIP devices.

Symptom 28-11. The POST (or software diagnostic) reports a fault in thefirst 64KB of RAM The first RAM page is important because it holds the BIOS Data


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Area (BDA) and interrupt vectors—the system will not work without it. When a RAM er-ror is indicated, your only real recourse is to replace the motherboard RAM. On oldermotherboards, if the diagnostic indicates which bit has failed and you can correlate the bitto a specific IC, you can sometimes replace the defective IC (typically, surface mounted).Otherwise, you will need to locate and replace all of the motherboard RAM, or replace themotherboard entirely. Newer motherboards utilize SIMMs or DIMMs for all systemmemory, so it should be relatively simple to cycle through each SIMM or DIMM with aknown-good unit and isolate the defective memory.

Symptom 28-12. The MCP does not work properly when installed on amotherboard when external caching is enabled Some non-Intel math co-processors or FPUs work in areas that must be non-cached. For example, a CyrixEMC87 MCP with an AMI Mark IV i386 motherboard has been known to cause thesetypes of problems. When MCP problems arise (especially during upgrades), try dis-abling the external cache through CMOS setup. As another alternative, try a differentmath co-processor.

Symptom 28-13. A “jumperless motherboard” receives incorrect CPU SoftMenu settings and now refuses to boot This might occur on a motherboard, suchas the Abit IT5V, and is usually caused by accidental settings during system configuration.Fortunately, this type of problem can be corrected by removing power from the mother-board—try turning off the system and unplugging it for several minutes. When you re-store power to the system, the CPU soft menu will automatically reset the CPU frequencyfor the lowest setting and allow the motherboard to boot. You can then go back into theCPU soft menu and correct any speed-setting errors. If this were a jumpered motherboard,you would need to find the CPU speed jumper and set it correctly.

Symptom 28-14. When installing two 64MB SIMMS, only 32MB of RAM aredisplayed when the computer is turned on The motherboard is probably using a430VX chipset that (although supporting 128MB of RAM) will not support 64MB mem-ory devices. The 430VX only supports the following memory devices:

■ 512K × 32 bit (2MB)■ 1M × 32 bit (4MB)■ 2M × 32 bit (8MB)■ 4M × 32 bit (16MB)

The layout for a 64MB SIMM is 16M × 32 bit, which isn’t in the preceding list. Whenyou install two 64MB SIMMs, the system will use the 4M- × 32-bit specification to cal-culate the memory, thus displaying 32MB. Unfortunately, this limitation of the mother-board cannot be corrected without upgrading the motherboard.

Symptom 28-15. A Creative Labs PnP sound board refuses to work on onemotherboard, but the board works just fine on another motherboard In thisissue, the PnP BIOS is usually at fault. Check with the motherboard manufacturer to seeif a BIOS update is available to correct PnP problems.


Symptom 28-16. The system CD-ROM drive refuses to work once an IDEbus master driver is installed This is almost always a driver problem, which is notinteracting properly with the IDE/EIDE bus controller on the motherboard. In almost allcases, you should update the IDE bus master driver or disable bus mastering completely.

Symptom 28-17. You cannot get an AMD 5x86 133MHz CPU to run on yourmotherboard Check your voltage first. The AMD 5x86 runs on 3.3 V, so you might needa voltage regulator in the CPU socket (the AMD CPU might already be damaged). Alsocheck your BIOS version—you might need an updated BIOS to support the AMD CPU prop-erly. Check your jumper settings next—the speed or CPU type selection is almost always setwrong. If you cannot jumper the motherboard correctly (i.e., 33MHz bus speed), then themotherboard itself is limited—it cannot enable the 4× internal CPU clock for the AMD 5x86.In this case, you will need to use a different CPU or replace the motherboard outright.

Symptom 28-18. You cannot get a Cyrix 5x86 CPU to run on your mother-board Check your voltage first. The Cyrix 5x86 uses 3.3 V, so you might need a volt-age regulator in the CPU socket (the Cyrix CPU might already be damaged). Also checkyour BIOS version—you might need an updated BIOS to support the Cyrix CPU properly.Check your jumper settings next—the speed (33MHz) or CPU-type selection is almost al-ways set wrong. If problems persist, you might need a different CPU or motherboard.

Symptom 28-19. You see the error message “System Resource Conflict”on the AMI BIOS POST display This error is generated by AMI PnP BIOS (althoughother PnP BIOS might produce similar errors) when the BIOS detects a resource conflictduring initialization. You might try to force the BIOS to reconfigure the conflicting re-source by pressing the <Insert> key during POST. If problems continue, you might needa BIOS update, which might be able to resolve assignment conflicts more intelligently.Otherwise, you might need to try to reconfigure the conflicting resource manually (dis-abling its PnP support), or remove the offending device entirely.

Symptom 28-20. The system hangs after using MEMMAKER under DOSThis is most prevalent with AMI’s WinBIOS, which cannot support the “highscan” optionused with EMM386.EXE. Be sure to disable the “highscan” option from EMM386 beforerunning MEMMAKER. You might also choose to upgrade the system BIOS to a more re-cent version, which might be more robust when testing memory.

Symptom 28-21. The Power management icon does not appear in the Win-dows 95 Control panel This occurs even though the APM parameter under the BIOSpower-management setup is enabled. This problem occurs if you do not enable the APMfunction before you install Windows 95. If you have already installed Windows 95, youmust re-install it. Before doing so, however, be sure that the APM function is enabled.

Symptom 28-22. Systems with a Western Digital 1.6GB HDD fail to booteven though BIOS recognized the presence of HDD This is a typical problemwith large hard drives, which often need additional time to start up after powering the sys-tem. Check your BIOS advanced setup and increase the “Power-on Delay” time. This


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should correct the problem. This problem might reoccur if CMOS default values are re-loaded or if CMOS contents are lost.

Symptom 28-23. After installing Windows 95, the system can no longerfind the CD-ROM drive on the secondary IDE channel You might also find thatthe IDE drives are running in MS-DOS “compatibility mode.” This problem occurs oftenwith motherboards using the Intel 430HX chipset—Windows 95 is not recognizing the In-tel 82371SB drive controller on the motherboard, which causes BIOS to disable the sec-ondary IDE channel—devices on the secondary channel are not being detected after thesystem is rebooted. In most cases, you can upgrade the BIOS to correct this problem ormove the IDE devices to a separate IDE controller. You might also be able to find an updateto the MSHDC.INF file, which will force Windows 95 to recognize the 82371SB controller.

Symptom 28-24. The system hangs up or crashes when the chipset-spe-cific PCI-IDE DOS driver is loaded This is a known problem with Micro-Star moth-erboards using a VIA VP1 chipset and Award BIOS 4.50PG. The problem is with theBIOS version and its interaction with the PCI controller portion of the VIA chipset. Up-grading the BIOS version should resolve the problem.

Symptom 28-25. The Pentium motherboard is unusually picky aboutwhich SIMMs it will accept This occurs even though the SIMMs are all within theproper type and rating. Consider several possible problems. First, Intel chipsets are verydiscriminating when it comes to memory speed, so be sure that the memory speed is wellwithin the required range (usually 70 ns or faster). Second, try changing the wait states inthe CMOS setup to a lower speed (e.g., 4-4-4-4). If your system works under this lowspeed, then increase the speed (e.g., 3-3-3-3, 3-2-2-2, 3-1-1-1, etc.) and keep trying untilthe best number has reached. Finally, the memory itself might be of questionable qual-ity—try good-quality memory, bought from a reputable vendor. Be sure that the vendoroffers a liberal return policy so that you can return questionable memory easily.

Symptom 28-26. You experience a problem with pipeline burst cache Thisis a recognized problem with UMC pipeline burst cache (especially on an Amptron moth-erboard). The problem can usually be solved by adjusting the cache control to 4-4-4-4 (thedefault in CMOS is typically 2-3-3-3). This will reduce performance, but it should stabi-lize cache operations.

Symptom 28-27. You get no display, or the system refuses to boot be-cause of the keyboard controller Notice that the video adapter proves out fine inanother system. This is a problem with the VIA 82C41 24-pin keyboard controller (espe-cially on the Amptron PM-7600 motherboard). A fault with the KBC might cause a “nodisplay” or “fail to boot” condition. The VIA 82C41 is extremely sensitive to damagefrom power-supply surges/spikes, and ESD damage. Replace the KBC or replace themotherboard with a more robust model.

Symptom 28-28. Your customer forgets their password The PC password isstored in the CMOS RAM, which is located in either the motherboard chipset or the real-


time clock chip. If it is stored in the chipset, the CMOS memory is backed up by a coin-shaped lithium battery (or other battery). If it is stored in the RTC chip, it has an internalbattery to back up the CMOS RAM. For the external battery, follow these steps: First,make a complete backup of the CMOS settings. Turn off the system, and remove the bat-tery for at least two hours. This should clear the CMOS setting and erase the password.For the RTC battery, follow these steps: Determine which RTC chip you have—the fivedifferent kinds of real-time clock CMOS chips are:

■ Dallas DS 12887 real time■ Benchmarc■ Dallas DS 12B887■ Dallas DS 12887A■ BQ3287A

For the Dallas DS 12887 and Benchmarc RTC chips, if you can boot to the A: prompt,flash the BIOS chip with the same boot block record, but different BIOS revision. For ex-ample, if you have a P/I P55TP4XE motherboard with BIOS revision 0202, flash the BIOSchip to BIOS revision 0115. A BIOS checksum error will be generated. Enter the CMOSsetup screen, reload setup defaults, then save and exit. At this point, the password has beencleared. You can flash the BIOS back to the original revision. If you can’t boot to the A:prompt, turn off the system, remove the BIOS chip, and insert another with the same bootblock record but different BIOS revision. Power on the system. A BIOS checksum error willbe generated. Turn off the system. Reinstall the original BIOS. Power on the system again,and hit <Del> to enter the BIOS setup screen. Reload the setup defaults, then save and exit.

For the Dallas DS 12887A, a jumper is on the motherboard, which clears the CMOS.Please check your manual for the location of this jumper (it will vary between mother-boards). Shorting this jumper should erase the system-configuration information (includ-ing password) stored in the CMOS. To clear the CMOS, be sure that the system is off.Short the jumper for a moment and then remove it. Do not leave this jumper shorted. Af-ter clearing the CMOS, the password should be erased. For the BQ3287A and DallasDS12B887 RTC chips, short the same jumper (as in the previous section), but be sure topower the system on and off before removing the jumper.

Symptom 28-29. You encounter problems with Western Digital hard dri-ves (the drives work on other systems) This type of problem has been identifiedwith Asus motherboards using Award BIOS with older Western Digital (~1.6GB) drives.Notice that problems do not appear in newer Western Digital drives. There are severalmeans of addressing the problems: First, disable the “Quick Power-on Self Test” in yourCMOS setup, and enable the “floppy seek” option. This will increase the time that thedrive gets to spinup. If your CMOS offers a “Power-on Delay Time” instead, try increas-ing that time. Also avoid using DEFRAG, or the “disk surface scan” feature of ScanDiskwith Western Digital drives—both have been reported to increase the number of badblocks on the disk.

Next, consider a BIOS upgrade (especially if you’re using a motherboard with the Intel430FX chipset). Some BIOS versions use a “park head” command that can cause prob-lems with Western Digital hard drives. Finally, check the Western Digital Web site


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(http://www.wdc.com) for any drive patches that might be currently available. If all elsefails, you can replace the drive outright.

Symptom 28-30. You encounter memory parity errors at bootup If you’re us-ing non-parity memory devices (e.g., a 32-bit device instead of a 36-bit device), you will needto disable DRAM ECC or parity checking through the CMOS chipset features settings. Thisproblem can occur if you reload default CMOS settings, which restores parity/ECC on a sys-tem with non-parity memory. Also, the Triton chipset does not support parity, so even if youuse parity RAM, you should try disabling parity checking. If the system is configured prop-erly, you might actually have a memory failure, and you’ll need to isolate the memory fault.

Symptom 28-31. You flash a BIOS, but now you get no video When you flasha BIOS, the CMOS settings are left useless. This means you will have to restore the properCMOS settings before the system might run properly. Clear your CMOS and reload theproper settings. The BIOS IC itself might also be troublesome. There are some problemswhen flashing an Intel flash ROM IC. Be sure that no warnings or cautions are in the systemdocumentation or from the manufacturer’s Web site before flashing a particular BIOS IC. Tryrestoring the original BIOS, if possible, or contact the manufacturer for a replacement BIOS.

Symptom 28-32. You are trying to use a PnP sound card and PnP modemtogether on the same system, but you’re getting hardware conflicts Thisis an all-too-common problem with PnP systems. In general, the modem should takeCOM2 (2F8h and IRQ3), and the sound card should take 220h, IRQ5, and DMA 1. Tryadding the cards one at a time—install the sound card first and let Windows 95 detect it.Add the modem next. If problems persist, configure the cards manually (disable their PnPsupport), if possible.

Symptom 28-33. After setting the DRAM speed to 70 ns in the Advancedchipset setup, the system crashes or refuses to boot Chances are that youhave the incorrect number of wait states set for your memory configuration—70-ns RAMtypically requires at least one wait state. Disable any “Auto configure DRAM timing” fea-ture, then set the number of wait states to 1. That should clear up the problem.

Symptom 28-34. 32MB (or more) of memory is installed, and the BIOScounts it all during POST, but you only see 16MB in the CMOS setup screenThis problem has been identified with some Award BIOS versions. To correct the problem,be sure that the “memory hole” option in the Advanced chipset setup area is disabled. The“memory hole” option assumes that a maximum of 16MB of physical RAM is in the system.

Symptom 28-35. You move a working IDE drive from an older 386/486 sys-tem to your new Pentium system, but the system no longer works In mostcases, the data-transfer mode is set improperly for the old IDE hard drive (e.g., using LBAmode when the IDE drive requires CHS mode). Find the Peripheral setup screen in yourCMOS setup and be sure to change all the PIO mode settings to Mode 0 (chances are thesettings are currently at Automatic, and are configuring the data transfer incorrectly). Insome cases, you might need to repartition and reformat the drive to use it on a different(older) controller.


Symptom 28-36. Windows 95 locks up when you install a Diamond StealthVideo 3200 board and an Intel EtherExpress Pro 10/100 network cardHowever, you verify that both cards work fine on other systems. Problems begin whenyou load the Intel network driver. This is a problem that has been identified with Premiomotherboards and is caused by a problem in the system BIOS. Upgrade the Premio BIOSto the latest version.

Symptom 28-37. You install an Intel Pentium P55C (MMX) 200MHz CPU,and you set the CPU speed jumper(s) for 200MHz, but the system still re-ports 166MHz In virtually all cases, you have set the speed jumper(s) incorrectly. Takeanother look at the documentation for your motherboard and see that the speed is indeedset correctly. If problems persist, the BIOS might not recognize the higher CPU speed cor-rectly, so try upgrading the motherboard BIOS.

Symptom 28-38. The system frequently locks up or crashes after in-stalling a Cyrix 6x86 CPU In most cases, the Cyrix 6x86 is not being cooled prop-erly and is overheating. Be sure that you have a heatsink/fan assembly attached properlyto the Cyrix chip, and see that the fan is running. Also, the Cyrix 6x86 P166+ is a 3.52-VCPU. Check your voltage regulator and see that it is set to provide 3.45 to 3.6 V.

Symptom 28-39. After installing a Pentium 120MHz motherboard, you get“registry corruption” or “out of memory” errors from Windows 95 This hap-pens most often with slightly older Pentium motherboards (~100 to 120MHz), and is al-most always a BIOS version problem, which causes the motherboard to misbehave underWindows 95. You will need to update the BIOS version for your particular motherboard.

Symptom 28-40. The motherboard fails to “auto-detect” the hard drive pa-rameters This is a known problem on Dataexpert EXP8551S motherboards, and iscaused by a problem with Windows 95 in recognizing the PCI/ISA/I/O controller portionof the chipset. You can use the following procedure to force Windows 95 to recognize thechipset properly:

1 Boot up the Windows 95 system normally2 Change the directory to /WINDOWS/INF3 Edit the hidden file MSHDC.INF4 Search for all lines with the “1230” device ID. Copy the lines and replace “1230” with

“7010” (the correct device ID)5 Save the file MSHDC.INF6 Remove the “Standard IDE/ESDI hard-disk controller” entry from the Device manager.7 Restart the computer, then choose the Windows default driver following the instruc-

tions shown on the screen.

If the problem persists, you should try entering the specific hard-drive parameters foryour particular drive into the CMOS setup.


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You should make a backup copy of the MSHDC.INF file before proceeding to edit the file.That way, you can easily restore the original file, if necessary.

Symptom 28-41. The motherboard refuses to detect the SCSI controllerduring bootup This problem has been identified with the Dataexpert EXP8551 moth-erboard, but it might occur on many different types of PCI motherboards. In most cases,you will have to change the configuration of your PCI slots on the motherboard. For ex-ample, if the SCSI controller is installed on slot 2, you will need to configure the PCI slot2 in CMOS setup.

Symptom 28-42. A Cyrix 6x86 CPU will not run on a particular mother-board This is a problem has been identified on Eurone/Matsonic motherboards, and isusually the result of an incompatible motherboard clock generator. Some clock generatorssupport the Cyrix 120, 133, and 166MHz models, but exempt the 200MHz model. Otherclock generators support the 120, 150, 166, and 200MHz models, but exempt the 133MHzmodel. So, if you’re using a 133MHz or 200MHz Cyrix CPU, you might be using the“wrong” clock generator. You will have to replace the CPU with a speed that is suitableto the particular clock generator, or change the motherboard to one that will accommodatethe particular CPU speed.

Symptom 28-43. The system can only count up to and recognize 8MB ofRAM, although the system can accommodate even more This problem is of-ten identified with Freetech 586F61x motherboards using Award BIOS version D or ear-lier. You can duplicate the problem by initiating a software reset with <Ctrl>+<Alt>+<Del>, then hitting the hardware reset—BIOS will only count memory up to 8MB. Youwill need to update the Award BIOS to version E or later. Freetech provides the BIOSpatch on their Web site.

Symptom 28-44. When four 8MB SIMMs are installed in the system(32MB), the system only counts up to 24MB This is a known problem with gi-gabyte motherboards (typically the GA-586ATE, ATM, and AP version 1.x). The moth-erboard does not support “double-sided” SIMMs (i.e., 2MB, 8MB, 32MB, or 128MB) inthe center bank. Install the SIMMs in bank 0 and bank 2—leaving bank 1 empty.

Symptom 28-45. Gold-plated SIMMs do not work properly in tin-platedsockets As a general rule, you should avoid mixing metal types when choosingSIMMs—the metal in the SIMM socket must be the same as the metal on the SIMM itself.Otherwise, tin debris will transfer to the gold surface and oxidize. This will eventually re-sult in memory failures, which suggests faulty SIMMs.

Symptom 28-46. Even though all peripherals in the system are SCSI, Win-dows 95 will continue to detect the PCI IDE controller You notice that this oc-curs even though the controller was disabled in CMOS. This is a known problem with theIwill P54TS motherboard. Normally, Windows 95 will try to recognize and try to enableI/O devices, but should not enable devices that are deliberately disabled in CMOS. This istypically a BIOS problem, so try upgrading your BIOS to the latest version.


Some motherboards require the banks to be filled in sequential order or allow you tochange the bank order with jumpers.

Symptom 28-47. An “EISA CMOS configuration error” occurs when thesystem starts For EISA systems, you must run the EISA configuration utility to prop-erly set up the system. Without this step, the system will not be able to detect any possi-ble resource conflicts. This type of problem is most common when installing a new EISAmotherboard, when CMOS contents are lost, or when devices (such as memory) are addedor removed.

Symptom 28-48. The SMP (dual processor) mode refuses to run in Win-dows NT The most common problem is an incompatibility with the SMP HAL shippedwith Windows NT (versions prior to 3.51) and the motherboard’s chipset. If you are up-grading from an older version of NT (prior to 3.51), first install NT as a standard PC (sin-gle-processor kernel), then install NT with the default multi-processor kernel that itprovides (NT will not recognize your dual CPUs if you upgrade straight to a multi-proces-sor configuration).

Symptom 28-49. When attempting to upgrade your flash BIOS, an “insuffi-cient memory” error occurs In most cases, you simply don’t have enough conventionalmemory available to execute the flash program. Most flash programs require about 560KBor conventional RAM. Try booting “clean” with a DOS diskette, then run the flash upgrade.

Symptom 28-50. A prolonged “Updating ESCD” message appears eachtime that the system boots The Extended System Configuration Data (ESCD) areais part of a PnP system. One or more PnP devices are attempting to update your BIOS set-tings. To stop this from occurring, set the BIOS to “program” mode.

Symptom 28-51. A yellow (!) sign appears over the USB port in the Devicemanager Windows 95 indicates that it has detected an unknown PCI device. In virtu-ally all cases, the proper driver for the USB on your system has not been installed, andWindows 95 cannot recognize the USB hardware. You can usually correct this problem byupdating your system BIOS to a newer version that supports the USB under Windows 95.

Symptom 28-52. The Device manager under Windows 95 indicates fourCOM ports (at unusual IRQs and I/O addresses), but only two physicalports are on the motherboard This problem has been identified with the OceanRhino motherboard, which is running a very old Award BIOS. The Award BIOS has sincebeen upgraded to provide full support for Windows 95, so download the newest BIOS ver-sion from the motherboard manufacturer.

Symptom 28-53. The performance of a motherboard with an AMD K5 CPUseems extremely poor This is almost always because of the motherboard BIOS—chances are the BIOS was released before the AMD K5 was widely introduced, so theremight be problems providing proper AMD support. Be sure that you are using the very lat-est BIOS that supplies adequate AMD support.

Symptom 28-54. The system hangs up after installing a Cyrix 6x86 CPUThe problem is probably with the utilization of system cache, which is causing the systemto hang up. Try disabling the internal (L1) and external (L2) cache.


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Symptom 28-55. When attempting to upgrade the BIOS version, a key se-quence, such as <Ctrl>+<Home>, cannot be used to reboot the PC in or-der to start the flash process The current BIOS version does not support such keysequences. To flash the BIOS, start the flash program manually from the DOS prompt.For example:

A:\> AMIFL PAIV17.ROM <Enter>

Symptom 28-56. A particular SVGA board refuses to work on a particularmotherboard However, the video board proves out fine on other systems. In mostcases, this is a compatibility problem between the video chipset and the motherboard. ABIOS upgrade for the motherboard or video board can overcome the problem. You mightsimply have to use a different video board.

Symptom 28-57. When the on-board printer port is set to 3BCh (and EPP/SPP mode) and another parallel port add-on card is set to 378h or 278h,the BIOS only recognizes the add-on card Port 3BCh seems to disappear. Thismight be a configuration problem with the Winbond chipset, which specifies that LPT1 onthe motherboard should be set at 378h (EPP or SPP), and add-on parallel ports should be setat 278h or 3BCh. The Winbond chip was designed this way for Windows 95. Check withthe motherboard manufacturer for any available BIOS upgrades that can correct this issue.

Symptom 28-58. With 32MB of RAM on the motherboard, Checkit 3.0causes the system to reboot when performing DRAM tests This is becauseCheckit 3.0 will not perform memory testing over 16MB. This is an issue with Checkit—not the motherboard. Upgrade to a later version of Checkit.

Symptom 28-59. The IBM Blue Lighting CPU will not run on a motherboardthat should support it In most cases, the problem is an older BIOS version. Be surethat you are running the latest version of BIOS before installing the IBM Blue Lightning.Also check to be sure that any CPU type and speed jumpers are set properly for the CPU.

Symptom 28-60. When using a benchmark program, such as SYSINFO, the“Overall Performance” rating of a Pentium 100 system marks better thana Pentium-120 system This is because of the PCI bus speed. For a 100MHz system,the PCI bus speed is 33MHz. For a 120MHz system, the bus speed is 30MHz. Theslightly faster PCI system will register a bit better performance.

Symptom 28-61. Parallel-port devices do not work on your motherboardIn most cases, you must set the proper parallel-port mode (i.e., SPP/ECP/EPP) for the par-ticular device you plan to use. Often, setting the port to Compatibility mode will work formany common peripherals. Parallel-port modes are selected through the CMOS setup—usually under “Integrated peripherals” or some similar heading.


Always be sure that your benchmark and diagnostic programs are updated for the CPUsand other hardware that you are testing.

Symptom 28-62. Some configurations of memory provide less perfor-mance than others This type of problem is most noted on motherboards with 440FXchipsets, and is usually the result of a BIOS problem. Try updating your BIOS to the lat-est available version.

Symptom 28-63. The performance does not improve when enablingPCI/IDE bus mastering The problem is often that you are using an older (or buggy)driver. Be sure that you have installed the most recent bus-mastering driver file (Triton I,Triton II and Natoma chipsets might use the same driver).

Symptom 28-64. The BIOS banner displayed at power-on is showing thewrong motherboard model In virtually all cases, this is a problem with the BIOSversion. Get the latest update for your motherboard BIOS.

Symptom 28-65. The Pentium P55CM BIOS shows a 150MHz CPU—eventhough the CPU is a 166MHz model This is almost always due to a BIOS fault.You should upgrade to the very latest BIOS version for your particular motherboard. Ifyou cannot flash the BIOS, replace the BIOS IC outright.

Symptom 28-66. “Static device resource conflict” error message occursafter the system memory count when using the P55CM CPU This problem isusually in the PCI bus system. Press and hold the <Insert> key before turning on the com-puter. Release the <Insert> key when the video comes up. This forces the system to reas-sign PCI resources. If the error message still appears, remove all PCI cards (except for thevideo card) and try again. Reinsert one PCI card at a time until the problem returns—thatis where the problem is.

Further StudyThat’s all for Chapter 28. Be sure to review the glossary and chapter questions on the ac-companying CD. If you have access to the Internet, take a look at some of these mother-board resources:

Abit Computer Corp.: http://www.abit.com.tw/html/emain.htm

Acer America Corp.: http://www.acer.com

American Megatrends (AMI): http://www.megatrends.com

American Predator Corp.: http://www.americanpredator.com

ASUS: http://www.asus.com

Biostar Microtech Intl.: http://www.biostar.net

CompuTrend Systems, Inc. (Premio): http://www.premiopc.com

Data Expert Corp.: http://www.dataexpert.com

FURTHER STUDY 965

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Diamond Flower, Inc. (DFI): http://www.dfiusa.com

Elitegroup Computers, Ltd. (ECS): http://www.ecs.com.tw

Famous Technology Co., Ltd.: http://www1.magic-pro.com.hk/famous/index.html

First International Computer, Inc. (FIC): http://www.fica.com

Fong Kai Industrial Co. (FKI): http://www.fkusa.com

Gemlight Computer Ltd.: http://www.gemlight.com.hk

Genoa Systems Corp.: http://www.genoasys.com

Giga-Byte Technology Co., Ltd.: http://www.giga-byte.com

Intel Corp.: http://www.intel.com

Iwill Computer: http://www.iwill.com.tw

Jbond: http://www.jbond.com

J-Mark Computer Corp.: http://www.j-mark.com

Kam-Tronic Computer Co., Ltd.: http://megastar.kamtronic.com

Micronics Computers, Inc.: http://www.micronics.com

Microway: http://www.microway.com

Micro Star International Co., Ltd. (MSI): http://www.msi.com.tw

PC Chips Manufacturing Ltd.: http://www.pcchips.com

Pine Technology Ltd.: http://www.pinegroup.com

Shuttle Computer International: http://www.shuttlegroup.com

Soyo Computer Inc.: http://www.soyo.com.tw

Supermicro Computer Inc.: http://www.supermicro.com

Tekram Technology: http://www.tekram.com

Tyan Computer: http://www.tyan.com


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