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.
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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