HDD Hardware Checks

If you cannot access the hard disk drive, and its configuration settings are correct, you must troubleshoot the hardware components associated with the hard disk drive. As previously indicated, these components include the drive, its signal cable, and the HDC. Like the FDC from the floppy disk drive, the HDC can be mounted on an adapter card, or it can be integrated into the system board. Normally, you must remove the outer cover form the computer to troubleshoot these components.

In a pre-Pentium system, the easiest component to check is the controller card that holds the HDD interface circuitry. Exchange the controller card with a known good one of the same type. Make certain to mark all the cards control signal cables before disconnecting them. Also, identify their connection points and direction. Your makings help to ensure their proper re-installation. Reconnect the disk drive signal cables to the new controller card.

Try to reboot the system from the hard drive. If the system boots up properly, check to see that all the DOS commands are working properly. Also, check the operation of all the hard disks software programs to make sure they are still functioning correctly. Reinstall any program that does not function properly.

The next logical step may seem to be to replace the hard drive unit. However, it is quite possible that the hard drive may not have any real damage. It may just have lost track of where it was, and now it cannot find its starting point. In this case, the most attractive option is to reformat the hard disk. This action gives the hard drive a new starting point to work from. Unfortunately, it also destroys anything that you had on the disk before you replace it may save the expense of buying a new hard disk drive that is not needed. Make certain to use the /S modifier, or repeat the SYS C: operation with the FORMAT command, to restore the system files to the hard drive..

If not, check the HDD signal cable for proper connection at both ends. Exchange the signal cables for a known good one. Check the HDD Drive select jumper and Master/Slave/Single jumper settings to make sure they are set correctly, as illustrated. Check to see whether the system might be using the cable select option also depicted. This setting requires a special CSEL signal cable designed to determine the master/slave arrangements for multiple IDE drives. Exchange the HDD power connector with another one from the power supply, to make certain that it is not a source of problems.

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BASIC HDD Checks

If the HDD configuration information is correct and you suspect a hard disk drive problem, the first task is to determine how extensive the HDD problem is place a clean boot disk in the A: Drive and try to boot the system. Then, execute a DOS DIR command to access the C:Drive if the system can see the contents of the drive, the boot files have been lost or corrupted, but the architecture of the disk is intact.

Modify the DOS DIR command with an /AH or /AS switch to look in the root directory for the system files and the COMMAND.COM file. It is common to receive a Disk Boot Failure message onscreen, if this type of situation occurs. The No (or Missing) ROM BASIC interpreter message may also be produced by this condition

If the clean boot disk has a copy of the FDISK program on it, attempt to restore the drives master boot record by typing the following:

A>FDISK /MBR

Providing that the hard disk can be accessed with DIR command, type and enter the following command at the DOS prompt

SYS C:

This command copies the IO.SYS, MSDOS.SYS, and COMMAND.COM system files from the DOS disk to the hard disk drive. Turn off the system, remove the DOS disk from the A: drive,and try to reboot the system from the hard drive.

If the system boots up properly, check to see that the operating system commands are functioning properly. Also, check to see that all installed software programs function properly. Recheck the installation instructions  of any program that does not function properly. Reinstall the software program if necessary.

Actually, three conditions produce a Bad or Missing COMMAND.COM error message. These conditions include the following:

* The first condition occurs when the COMMAND.COM file cannot be found on the hard drive, and no bootable disk is present in the A:drive

* The COMMAND.COM file is not located int he hard drives root directory. This message is likely when installing a brand new hard drive or a new DOS version.

* The message also occurs if the user inadvertently erases the COMMAND.COM file from the root directory of the hard drive.

If the system cannot see the drive after booting to the floppy disk drive, an Invalid Drive message or an Invalid Drive Specification message should be returned in response to any attempt to access the drive. Under these conditions, you must examine the complete HDD system. Use the FDISK utility to partition the drive. Next, use the FORMAT/S command to make the disk bootable. Any data that was on the drive will be lost in the formatting process, But it was already gone because the system could not see the drive.

Attempt to run a diagnostic software program, if possible, Try to use a diagnostic programs HDD Tests, and perform the equivalent of the All Tests function.

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HDD Configuration Checks

While booting up the system, observe the BIOS's HDD type information displayed on the monitor. Note the type of HHD that the BIOS believes is installed in the system. The values stored in the CMOS memory must accurately reflect the actual HDDs format installed in the system. otherwise an error occurs. Possible error messages associated with HDD configuration problems include the Drive Mismatch Error message and the Invalid Media Type message. You can access these values for change by pressing the Ctrl and Del key simultaneously, during the bootup procedure.

If the HDD is used with a system board mounted controller, check for the presence of an HDD enabling jumper on the system board. Make certain that it is set to enable the drive, if present. Check the drive to make sure that it is properly terminated. Every drive type requires a terminating block somewhere in the interface. On system level drives, check the master slave jumper setting to make sure that it is set properly for the drives logical position in the system.

If you have more than one device attached to a single interface cable, make sure that they are of the same type. Mixing device types will create a situation in which the system cannot provide the different types of control information each device needs. The drives are incompatible and you may not be able to access either device.

If the drive is a SCSI drive, check to see that its ID has been set correctly and that the SCSI chain has been terminated correctly. Either of these errors results in the system not being able to see the drive.Also check the CMOS setup utility to make sure that SCSI support has been enabled, Along with large SCSI drive support.

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HARD DISK DRIVE PROBLEMS

Typical symptoms associated with hard disk drive (HDD) failures include the following:

* The computer does not boot up when turned on.
* The computer boots up to a sysmtem disk in the A: drive, but not to the hard drive, indicating that the systme files on the HDD are mising or have become corrupt.
* No motor sounds are produced by the HDD while the computer is running.
* An IBM compatible 17xx error code is produced on the monitor screen.
* An HDD Controller Filure message displays, indicating a failure to verify hard disk setup by system configuration file error.
* A C: or D: Fixed Disk Drive Error message display, indicating a hard disk CMOS setup failure.
* An Invalid Media Type Message displays, indicating the controller cannot find a recognizable track sector pattern on the drive.
* A no Boot Record Found, a Non-System Disk or Disk Error, or an Invalid System Disk message displays, indicating that the system boot files are not located in the root directory of the drive.
* The video display is active, but the HDDs activity light remains on and no boot up occurs, indicating that the HDDs CMOS configuration information is incorrect.
* An Out Of Disk Space message displays, indicating that the amount of space on the disk is insufficient to carry out the desired operation.
* A Missing Operating System, a Hard Drive Boot Failure, or an Invalid Drive or Drive Specification message displays, indicating that the disks master boot record is missing or has become corrupt.
* A No ROM BASIC System Haltedd, or ROM BASIC Interpreter Not Found Message displays, followed by the system stopping, indicating that no master bot record was found in the system. This message is produced only by PCs, XTs, and osme clones.
* A current drive no longer valid message displays, indicating that the HDDs CMOS configuration information is incorrect or has become corrupt.

HDD Configuration Checks
BASIC HDD Checks
HDD Hardware Checks

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Monitor Problems Toubleshooting

All the circuitry discussed so far is part of the computer or its video adapter unit. The circuitry inside the monitor is responsible for accepting, amplifying, and routing the video and synchronizing information to the CRT's electron guns and the deflection coils.

Monitor Handling
Show in figure, Components located inside a typical CRT (Cathode Ray Tube) color monitor. Of particular interest is the high voltage anode that connects the tube to the high voltage sections of the signal processing board. This is a very dangerous connection that is not to be touched.

Operation of a monitor with the cover removed poses a shock hazard from the power supply. Therefore, any one unfamiliar with the safety precautions associated with high voltage equipment should not attempt servicing.

The high voltage levels do not necessarily disappear because the power to the monitor is turned off. like television sets, monitors have circuitry capable of storing high voltage potentials long after power has been removed. Always discharge the anode of the picture tube to the receiver chassis before handling the CRT tube. Due to the high voltage levels, you should never wear antistatic grounding straps when working inside the monitor.

An additional hazard associated with handling CRTs is that the tube is fragile. Take extra care to prevent the neck of the tube from striking any surface. Never lift the tube by the neck especially when removing or replacing a CRT tube in the chassis. If the picture tubes envelope is cracked or ruptured, the inrush of air will cause a high velocity implosion, and the glass will fly in all directions. Therefore, you should always wear protective googles when handling picture tubes.

Color monitors produce a relatively high level of X radiation. The CRT tube is designed to limit X radiation at its specified operating voltage. If a replacement CRT tube is being installed, make certain to replace it with one of the same type, and with suffix numbers that are the same. You can obtain this information from the chassis schematic diagram inside the monitors housing.

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Mouse Problems Troubleshooting

The levels of mouse troubleshooting move from configuration problems to software problems including command line, windows, and applications to hardware problems.
Maintenance of the mouse if fairly simple. Most of the problems with mice involve the trackball. As the mouse is moved across the table, the trackball picks up dirt or lint, which can hinder the movement of the trackball, typically evident by the cursor periodically freezing and jumping onscreen. On most mice, you can remove the trackball from the mouse by latching mechanism on it bottom. Twisting the latch counter clockwise enables you to remove the trackball. Then you can clean dirt out of the mouse.

Basic Mouse Checks

When the mouse does not work in a windows system, restart it and move into safe mode by pressing the F5 function key when the starting windows message displays This action starts the operationg system with the most basic mouse driver available.

If the mouse will not operate in safemode, restart the system and check the CMOS setup screen during boot up for the presence of the serial port that the mouse is connected to.

If the mouse work in safe mode, click the mouse icon in the control panel to check its configuration and settings. follow this by checking the port configuration in window control panel. Consult the device manager entry under the control panels system icon. Select the ports option, click the COMs properties option in the menu, and click resources. Make certain that the selected IRQ and address range match that of the port.

Click on the mouse entry in the device manager and double click its driver to obtain the mouse properties. Move to the resources tab and check the IRQ and base address settings for the mouse in windows. Compare these settings to the actual configuration settings of the hardware. If the differ, change the IRQ or base address setting in Windows to match those of the installed hardware.

If the correct driver is not available in the windows list, place the manufacturers driver disk in the CD/DVD Drive and load it using the other mouse. If the OEM driver fails to operate the mouse in windows, contact the mouse manufacturer for an updated windows driver. windows normally supports only mice on COM1 and COM2. If several serial devices are being used in the system, you might have to establish alternative IRQ settings for COM3 and COM4

In older systems, check the directory structure of the system for a mouse directory. Also, check for AUOTEXEC.BAT and CONFIG.SYS files that may contain conflicting device drivers. Two common driver files may be present; the MOUSE.COM file called for in the AUTOEXEC.BAT file; and the MOUSE.SYS file referenced in the CONFIG.SYS file. If these files are present and have mouse lines that do not begin with a REM statement, they could be overriding the settings in the operating system. In particular, look for a Device command associated with the mouse.

Mouse Hardware Checks

If the 2/3 button switch and driver setup is correct, you must divide the port circuitry in half. For most systems, this involves isolating the mouse from the serial port. Just replace the mouse to test its electronics.

If the replacement mouse works, the original mouse is probably defective. If the electronics are not working properly. few options are available for servicing the mouse. It may need a cleaning, or a new trackball. However, the low cost of a typical mouse generally makes it a throwaway item if simple cleaning does not fix it.

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Keyboard Problems Troubleshooting

Most of the circuitry associated with the computers keyboard is contained in the keyboard itself. However, some keyboard interface circuitry is located on the system board. Therefore the steps required to isolate keyboard problems are usually confined to the keyboard, its connecting cable, and the system board.

This arrangement makes isolating keyboard problems relatively easy. Just check the keyboard and the system board.

Keyboard Symptoms

Typical symptoms associated with keyboard failures include the following:

* No characters appear onscreen when entered from the keyboard.
* Some keys work, whereas others do not work.
* A keyboard is locked unlock it error displays.
* A keyboard error keyboard test failure error displays.
* A KB/Interface error keyboard test failure error displays.
* An error code of 6 short beeps is produced during boot up.
* Wrong characters display.
* An IBM compatible 301 error code displays.

Basic Keyboard Checks

Keyboard information is stored in the CMOS setup memory, and must accurately reflect the configuration of the system; otherwise, an error occurs. In most CMOS screens, the setup information includes keyboard enabling, Numlock key condition at startup, typematic rate, and typematic delay. The typematic information applies to the keyboars capability to repeat characters when the key is held down. The typematic rate determines how quickly characters are repeated, and the delay time defines the amount of time the key can be held before typematic action occurs. A typical typematic rate setting is 6 characters per second; the delay is normally set at 250 milliseconds.

As with other components, the only time a configuration problem is likely to occur is when the system is being set up for the first time or when a new option is installed. The other condition that cusses a configuration problem involves the system boards CMOS backup battery. If the battery fails, or has been changed, the contents of the CMOS setup will be lost. After replacing the battery, you must always run the setup utility to reconfigure the system.

Turn on the system and observe the BIOS screens as the system boots up. Note the keyboard type listed in the BIOS summary table. If possible, run a selected diagnostic program to test the keyboard. Run the programs keyboard test function, and perform the equivalent of the All test function if available. These test are normally very good at testing the keyboard for general operation and sticking keys.

If the keyboard produces odd characters on the display, check the windows keyboard settings in the control panel device manager. If the keyboard is not installed, or is incorrect, install the correct keyboard type. Also, make certain that you have the correct language setting specified under the control panels keyboard icon.

Keyboard Hardware checks

If you suspect a hardware problem, you must first isolate the keyboard as the definite source of the problem. Because the keyboard is external to the system unit, detachable, and inexpensive, begin by exchanging the keyboard with a good keyboard. If the new keyboard works correctly, return the system to full service and service the defective keyboard appropriately.

To service a defective keyboard remove the back cover of the keyboard and check for the presence of a fuse in the +5v (DC) supply and check it for continuity. Disconnecting or plugging in a keyboard with this type of fuse while power is on can cause it to fail. If the fuse is present, Just replace it with a fuse of the same type and rating.

If the system still wont boot up. recheck the CMOS setup to make sure that the keyboard is enabled. Check the keyboard cabling for continuity. And, finally, check the video display system (monitor and adapter card) to make sure that it is functional.

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Troubleshooting Problems With Facebook

The origin of Facebook, Initially known as thefacebook, Mark Zuckerberg founded Facebook while studying at Stanford University along with collage mates Eduardo Saverin, Dustin Moskovitz, and Chris Hughes on Feb 4, 2004.

The controversy around Facebook started quickly.  A week after he released the website in 2004, Zuckerberg was charged by three Stanford senior students, Cameron Winklevoss, Tyler Winklevoss, and Divya Narendra of having thieved the idea from them. Zuckerberg faced charges of violation of security, breaking copyrights, and breaking individual comfort for taking the university student images he used to promote the website. He also experienced expulsion from Harvard University for his activities. However, all charges were gradually dropped.

Facebook is the largest online social networking service on the web, Primarily focused on high school to college students. Within months, Facebook and its primary idea distribute across the dorms of Harvard  University where it was very well received. Soon enough, it was prolonged to Yale and Stanford Universities.

The network was quickly extended to other Boston universities and eventually all US colleges. It became Facebook.com in 2006 after the address was purchased for $200,000.

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Exchanging the System Board

If possible, back up the contents of the systems hard drive to some other media before removing the system board. Also, record the CMOS configuration settings, along with the settings of all jumpers and switches, before exchanging the system board.

Remove the video and disk drive controller cards from the system boards expansion slots. Disconnect the system board from the power supply unit and the system board front panel connections. Take care to make any connection removed from the system board, and its connection point, to ensure proper reconnection. Exchange the system board with a known good one. Reconnect all the power supply and front panel connections to the system board. Reinstall the video and disk drive controller cards in the expansion slots and try to reboot the system.

Reconfigure the system board to operate with the installed peripherals. Reset the video and disk drive controller cards in the system unit. Reset the CMOS setup to match the installed peripherals and turn on the system.

When the system boots up, reinstall any options removed from the system and replace the system units outer cover. Return the system to full service and service the defective system board. If the system still does not boot-up. retest all the system components one at a time until you find a cause. Check the small things such as cable connections and key switches carefully.

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Motherboard Hardware Checks

If the systems CMOS configuration setup appears to be correct and a system board hardware problem is suspected, you probably need to exchange the system board for working unit. However, a few items are worth checking before doing so.

Check the system board for signs of physical problems, such as loose cables and devices. If noting is apparently wrong, check the power supply voltage levels on the system board. Check for +5V and +12V (DC) on the system board. If these voltages are missing, turn off the system, disconnect power to all disk drives, and swap the power supply unit with a known good one.

On-board FRU Devices

Finally check the FRU devices present on the board. Normally, a few serviceable items on the system board might be checked by substitution before doing so. These include the RAM modules, the microprocessor (and its cooling fan), the ROM BIOS chips. and the system battery.

* RAM: These system boards memory is a very serviceable part of the system. RAM failures basically fall into two major categories and create two different types of failures. The first category of memory errors, glitches int he operation of applications and the system. You can clear these events just by restarting the system. However, the other category of RAM failures are referred to as hard memory errors. These are permanent physical failures that generate NMI errors int he system and require that the memory units be checked by substitution.

You can swap the RAM modules out in a one at a time manner, to isolate defective modules. These modules ae also swapped out when a system upgrade is being performed. The burn-in tests in most diagnostic packages can prove helpful in locating borderline RAM modules.

Take care when swapping RAM into a system for troubleshooting purpose to make sure that the new RAM is the correct type of RAM for the system and that it meets the systems bus speed rating. Also, make sure that the replacement RAM is consistent with the installed RAM. Mixing RAM types and speeds can cause the system to lock up and produce hard memory errors.

* MICROPROCESSOR: int he case of the microprocessor failure, the system may issue a slow, single beep, with no display or other I/O operation. This indicates that an internal error has disabled a portion of the processor's internal circuitry (usually the internal cache). Internal problems also may allow the microprocessor to begin processing, but then fall as it attempts operations, Such a problem results in the system continuously counting RAM during the boot up process. It also may lockup while counting RAM during the boot up process. It also may lockup while counting RAM. In either case, the only way to remedy the problem is to replace the microprocessor.

You can easily exchange the microprocessor on most system boards. Only the 80386SX is a soldered in device. However, the fact the most microprocessors, as well as the BIOS chips, are mounted in sockets brings up another point. These items should be pulled and reseated in their sockets. If they seem to be a possible cause of problems. Sockets are convenient for repair and upgrade purposes. But they also can attract corrosion between the pins of the device, and those of the socket. Over time, the corrosion may become so bad that the electrical connection becomes too poor for the device to operate properly.

* ROM: Like the microprocessor, a bad or damaged ROM BIOS typically stops the system dead. When you encounter a dead system board, examine the BIOS chips for physical damage. If these devices overheat, it is typical for them to crack or blow a large piece out of the top of the IC package. Another symptom of a damaged BIOS is indicated by the boot up moving into the CMOS configuration, but never returning to the boot up sequence. In any case, you must replace the defective BIOS with a version that matches the chip-set used by the system.

* Battery: Corrosion also can affect the system clock over time. If a system refuses to maintain time and date information after the backup battery has been replaced, check the contacts of the holder for corrosion. Two types of batteries are commonly used for CMOS backup: Nickel Cadmium (Ni-Cad) and lithium batteries. Of the two, Ni-Cads have historically been the most favored. Conversely, Lithium batteries are gaining respect due to their long life capabilities when installed in system designed to recharge lithium batteries. However, Lithium battery life is noticeably short when they are installed in systems designed for the higher current drain Ni-Cads. Therefore, you should always use the correct type of battery to replace a system board battery.

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Motherboard Software Checks

Boot up the system and start the selected diagnostic program if possible. Try to use a diagnostic program that deals with the system board components. It should include memory, microprocessor, interrupt, and DMA tests.

Run the programs system board tests function and perform the equivalent of the all test function. These types of tests are particularly good for detecting memory errors, as well as interrupt and DMA conflicts. Note all the errors indicated by the tests. If a single type of error is indicated, you might be able to take some corrective actions, such as replacing a memory module or re-configuring interrupt/DMA settings, without replacing the system board. If more complex system board problems are indicated, however, exit the diagnostic program and use the following hardware checks and installation/removal procedure to troubleshoot and replace the system board.

You can use the DOS MEM command (MEM.EXE) to view the system's memory utilization scheme. It displays bothe the programs currently loaded into memory, and the systems free memory areas. You can use the /C switch with the MEM command as a valuable tool to sort out TSR conflicts in upper memory. Likewise, you can add a /D switch to the MEM command to view detailed information about memory usage. This switch gives very detailed information about all items stored in memory.

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Motherboard Configuration Checks

Observe the boot-up RAM count to see that it is correct for the amount of physical RAM actually installed in the system. If not, swap RAM devices around to see whether the count changes. Use logical rotation of the RAM devices to locate the defective part.

Normally, the only time a configuration problem occurs is when the system is being set up for the first time, or when a new option is installed. The other condition that causes a configuration problem involves the system boards CMOS backup battery. If the battery fails, or has been changed, the contents of the CMOS setup will be lost. After replacing the battery, it is always necessary to run the CMOS setup utility to reconfigure they system.

The values stored in CMOS must accurately reflect the configuration of the system; otherwise, an error occurs. You can access these values for change by pressing a predetermined key combination during the boot-up procedure.

In Pentium-based systems, check the advanced CMOS configuration and enabling setting in the BIOS and chipset features screens. These settings, illustrated in figure 2.4, usually include the disk drive, keyboard, and video options, as well as on-board serial and parallel ports.

In addition, the user can turn on or off certain sections of the systems RAM for shadowing purpose and establish parity or non-parity memory operations.

Incorrectly set BIOS enabling parameters cause the corresponding hardware to fail. Therefore, check the enabling functions of the advanced CMOS settings as a part of every hardware configuration troubleshooting procedure.

In some BIOS, holding down the Del key throughout the startup erases the CMOS contents and starts from scratch. Jumpers that can be set to start the contents from a bare-essentials setting may also be placed on the system board. In either case, you must rebuild any advanced features in the CMOS configuration afterward.

Newer system boards have an auto-configuration mode that takes over most of the setup decisions. This option works well in the majority of applications. Its settings produce an efficient, basic level of operation for standard devices in the system. However, they do not optimize the performance of the system. To do that, you must turn off the auto-configuration feature and insert desired parameters into the configuration table. There are typically two options for the auto-configuration function.

* Auto-configure with Power-On Defaults
* Auto-configure with BIOS Defaults

Using power-on defaults for auto-configuration loads the most conservative options possible into the system from the BIOS. This is the most effective way.

Typically, if the boot-up process reaches the point where the system CMOS configuration information displays onscreen, you can safely assume that no hardware configuration conflicts exist in the systems basic components. After this point in the boot-up process, the system begins loading drivers for optional devices and additional memory. If the error occurs after the CMOS screen displays and before the boot-up tone, you must clean boot the system and single step through the remainder of the boot-up sequence.

The many configuration options available in a a modern BIOS requires the user to have a good deal of knowledge about the particular function being configured. Therefore, an extended discussion of the advanced CMOS setup options cannot be conducted at this point . However, such information is covered along with the system component it relates to as the course moves through various system components.

CMOS setup utilities may also offer a wide array of exit options. One common mistake in working with CMOS configuration settings is that of not saving the new settings before exiting. When this happens, the new settings are not stored, and so that old settings are still in place when the system reboots.

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SYSTEM BOARD SYMPTOMS

So much of the systems operation is based on the system board that it can have several different types of symptoms. Typically symptoms associated with system board hardware failures include the following:

* The On/Off indicator lights are visible, the display is visible on the monitor screen, but there is no disk drive action and the machine does not boot up.
* The On/Off indicator lights are visible, the hard drive spins up, but the system appears dead and there is no boot up.
* The system locks up during normal operation.
* The system produces a beep code with 1,2,3,5,7 or 9 beeps.
* The system produces a beep code of 1 long and 3 short beeps.
* The system will not hold date and time.
* An 8042 Gate A20 Error message displays error getting into protected mode.
* An Invalid Switch Memory Failure Message displays.
* A DMA ERROR message displays DMA controller failed page register test.
* A CMOS Battery Low message display, indicating failure of CMOS battery or CMOS checksum test.
* A CMOS System Option Not Set message displays, indicating failure of CMOS battery or CMOS checksum test.
* A CMOS Checksum Failure message dsiplays, indicating CMOS battery low or CMOS checksum test failure.
* A 201 error code displays, indicating a RAM failure.
* A parity check error message displays, indicating a RAM error.

Typical symptoms associated with system board setup failures include the following:

* A CMOS inoperational message displays, indicating failure of CMOS shutdown register.
* A Display Switch Setting Not Proper message displays failure to verify display type.
* A CMOS Display Mismatch message displays failure of display type verification.
* A CMOS Memory Size Mismatch message displays system configuration and setup failure.
* A CMOS Time & Date Not Set message displays System configuration and setup failure.
* An IBM compatible error code displays, indicating that a configuration problem has occurred.

Typical symptoms associated with system board I/O failure include the following:

* Speaker doesn't work during operation. The rest of the system works, but no sounds are produced through the speaker.
* Keyboard does not function after being replaced with a known good unit.

Most of the hardware problems that occur with computers, outside of those already described, involve the system board. Because the system board is the center of virtually all the computers operations, it is only natural that you must check it at some paint in most troubleshooting efforts. The system board normally marks the end of any of the various troubleshooting schemes given for different system components. It occupies this position for two reasons. Firs the system board supports most of the other system components, either directly or indirectly. Second, it is the system component that requires the most effort to replace and test.

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System Board Problems

Problems related to the system board can be difficult to solve because of the system boards relative complexity. So many system functions rely at least partially on the system board that certain symptoms can be masked by other symptoms.

Begin by observing the symptoms produced by boot up and operation. Observe the steps that lead to the failure and determine under what conditions the system failed. Were anay unusual operations in progress? Note any error messages or beep codes. Retry the system several times to observe the symptoms clearly. Take time to document the problem write it down.

Refer to the user manuals for the system board and peripheral units to check for configuration problems. Examine the CMOS setup entries for configuration problems. In pentium system, also check the advanced CMOS setup parameters to make certain that all the appropriate system board enabliling settings have been made.

If possible, run a software diagnostics package to narrow the possible causes. There are many free diagnostic packages, PC Check is on such utility. Remember that the microprocessor, RAM modules, ROM BIOS, CMOS battery, and possibly cache ICs are replaceable units on the system board. If enough of the system is running to perform tests on these units, you can replace them. If sysmptoms suggest that one or more of these devices may be defective, you can exchange them with a known good unit of the same type.

If teh diagnostics program indicates a number of possible bad components, replace them one at a time until you isolate the bad unit. Then insert any possible good units back into the system and check them. You also should consider the possibility of bad software when multiple filed replaceable unit(FRU) problems are indicated

SYSTEM BOARD SYMPTOMS
CONFIGURATION CHECKS
SOFTWARE CHECKS
HARDWARE CHECKS
EXCHANGING THE SYSTEM BOARD

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Power Supply Problems

If the front panel lights are on and the power supply fan is running, but no other system action is occurring, you should consider the power supply as one of the most likely sources of such a problem.

The presence of the lights and the fan operation indicate that power is reaching the system and that at least some portion of the power supply is functional. This type of symptom results from the following two likely possibilities:

1. A portion of the power supply has failed, or is being overloaded. One or more of the basic voltages supplied by the power supply is missing while the other are still present.

2. A key component on the system board has failed, preventing it from processing, even though the system has power. A defective capacitor across the power input of the system board can completely prevent it from operating.

Check the power supply by substitution. If the power supply is not the cause of the dead system, one of the other components must be overloading the portion of the power supply. You must sort out which component is causing the problem.

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Checking a Dead System

Special consideration must be taken when a system is inoperable. In a totally inoperable system, there are no symptoms to give clues where to begin the isolated process. In addition, it is impossible to use troubleshooting software or other system aids to help isolated the problem.

The following discussion covers a standard method of troubleshooting dead microprocessor based equipment. The first step in troubleshooting any dead system is to visually inspect the system. Check for unseated cards, loose cables, or foreign objects within the system unit.

When the system exhibits no signs of life including the absence of lights the best place to start looking for the problem is at the power supply. The operation of this unit affects virtually every part of the system. Also , the absence of any lights working usually indicates that no power is being supplied to the system by the power supply.

1. Begin by checking the external connections of the power supply. This is the first step in checking any electrical equipment that shows no signs of life.
2. Confirm that the power supply cord is plugged into a functioning outlet.
3. Check the position of the ON/Off switch.
4. Examine the power cord for good connection at the rear of the unit.
5. Check the setting of the 110/220 switch setting on the outside of the power supply. The normal setting for equipment used in India is 22O.
6. Check the power at the commercial receptacle using a voltmeter, or by plugging in a lamp (or other 220v device) into the outlet.

If power is reaching the power supply and nothing is happening, the next step in isolating the cause of the problem is to determine which component is causing the problem. The most likely; cause of the problems is a totally dead system is the power supply itself. However, in a ATX system, if the cable that connects the system board to the power switch has become loose, the power supply will appear dead. Use a voltmeter to check for the proper voltages at one of the systems option power connectors. If any voltage is missing. check the power supply by substitution.

If the main power supply is not the reason the system is dead, one of the other components must be overloading the systems power supply. Under such conditions, it is normal for the system to trip the breaker, or to blow the fuse, in the commercial power system. You must sort out which components is affecting the power supply. Remove the peripheral devices so that only the basic system needs to be checked.

Divide the system into basic and optional sections for testing. Remove all external options from the system and restart the system. If the system begins to work, troubleshoot the optional portions of the system.

Finally, divide the basic system into optional and basic components. Remove all optional adapter cards from their expansion slots and restart the system. If the system begins to work, troubleshoot the various optional adapters by reinstalling them one at a time until the system fails again.

Note:
Before changing any board or connection, always turn the system off first. In an ATX style system, you should also disconnect the power cable from the power supply. This is necessary because even with the power switch off, there are still some levels of voltages applied to the system board in these units.

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Desktop Power Supply Problems

Typical Symptoms associated with power-supply failures include the following:

* No indicator lights visible, with no disk drive action, and no display onscreen. Nothing works; the system is dead.
* The On/Off indicator lights are visible, but there is no disk drive action and no display on the monitor screen. The system fan may or may not run.
* The system produces a continuous beep tone.

The power-supply unit is one of the few components in the system that is connected to virtually every other component in the system. Therefore, it can affect all the other components if it fails.

While tracking down power-supply problems it must be kept in mind that in addition to the obvious power connections. The power supply also delivers power to other components through the system board. These include:

1. All the options adapter cards(through the expansion-slot connectors)
2. The keyboard (through the keyboard connector)

Power-supply problems can cause symptoms to occur in all of these areas, and problems in any of these areas can affect the operation of the power supply.

CHECKING A DEAD SYSTEM

OTHER POWER-SUPPLY PROBLEMS

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