PC motherboard fault repair skills

1. familiar with the bus type of the PC motherboard and the signal arrangement in the I/O bus slots. finding fault points based on the important signals in the I/O slots is the key to repairing the fatal fault of the PC motherboard. The commonly used bus types of the Microcomputer motherboard include PC/XT, PC/AT, Vesa, and PCI. the CITIC numbers in the I/O slots of different bus vary, familiar with the important signals in the I/o slot is the prerequisite for finding serious faults such as system crashes due to bus faults and no display on the screen.

For dead-end faults, identify whether the fault is caused by an I/O device fault or the failure of the motherboard.

Fault. After the fault is confirmed on the system board, the pulse status of the address bus or data bus in the I/O slot of the system board can be checked to preliminarily determine the System Fault Location: If no pulse exists for all the address bus or data bus, the CPU may not work. If the IP address bus or data bus is a constant level and the other bit is a pulse, the bus is faulty. Because the failure rate of the CPU itself is low, check whether the CPU is not working properly from the CPU input signal.

The CPU has three basic operating conditions: system reset signal reset, system clock signal CLK, and CPU ready signal ready.

Taking PC/AT machine as an example, the 29-pin CPU (intel286) is a reset signal, which corresponds to the B02 reset DRV signal in the I/O slot. There should be an obvious positive pulse at startup; the 31-pin CPU is a CLK signal, which corresponds to the clock sysclk signal in the B20 slot in the I/O slot. It should be a TTL-level clock pulse. The 65-foot CPU is a ready signal, which should be a low level or pulse at startup. When a PC or at machine crashes, no fault is displayed on the screen. First, check that the B02 reset DRV signal in the I/O slot is always low, indicating that the reset signal is incorrect, as a result, we checked the clock processing chip 82284-12, and there was a positive pulse at startup, indicating that 82284 had correctly issued the system reset signal and tracked the reset signal transmission path for a downward check, note that the system reset signal has been correctly issued by 82284, and the transmission path of the reset signal is tracked down and the input of the 5 and 6 feet of 74als02 is a positive pulse, however, the output 4-pin is "not high, not low" floating level. After the chip is changed, the fault will be rectified. The principle of bus troubleshooting is: if one or a few digits are found to be at a constant level, you can restart the system to check whether these digits are at a constant level at the moment of startup, if the power-on instant is a constant level, it is an error state; if the power-on instant is a pulse and then changes to a constant level, you should first check other signals; if an error occurs when eight or more digits are detected, check whether the CPU is working normally or the control signal of the corresponding bus driver door (such as the direction control signal of the driver door or the selected communication number of the door ).

■ 2. I/o troubleshooting techniques for abnormal device operation

The operation of I/O equipment involves the operation of I/O equipment (such as printers, monitors, software and hard disks) itself, connection cables,

Multi-function card and motherboard. After a fault occurs on the Main Board through the replacement method and plugging method, it is easy to eliminate the fault by grasping the important control signals related to the peripherals on the main board and learning about the functions of the large-scale integrated circuit chip.

If the floppy drive motor turns on but does not read the floppy drive. Because the DMA Operation is used between the motherboard and peripherals such as the software and hard disk, the DMA Operation response process is as follows (taking the disk DMA in ast386 as an example ): first, the disk drive sends the dreq2 signal to the DMA controller (82c206), and then the DMA controller sends the hrq signal to the CPU (80386). After the CPU ends the current bus cycle, it returns the hlda signal to the DMA controller, the DMA controller sends the DMA response signal dack2 to the floppy drive.

To allow its data to enter the system bus.

Grasping the signals and transmission channels of dreq2, hqr, hlda, and dack2 can quickly locate the faulty location. In addition, interruptions play a very important role in peripheral operations.

It is also necessary to take into account the failure of peripheral operations involving interruptions in the transmission channel of the broken control signal. The Control Circuit of the main board is more complex. Fortunately, the control function is highly centralized and the transmission path is simplified. As long as the important control signal is grasped to locate the fault of the Main Board, the speed is faster than that of the early troubleshooting based on discrete components.

■ 3. Random fault repair skills

The causes of random faults are complex, and there is poor contact between chips or devices connected to the system through connectors;

The timing control circuit occasionally experiences Time Series Signal drift, and the level matching between chips is not good in a timely and orderly manner (for example, some compatible

Memory chip read/write speed is inconsistent); circuit board wiring is unreasonable or other reasons cause chip pins on the motherboard to generate

Capacitor or inductance may cause random faults. Such faults are manifested in memory error, memory verification error, and keyboard input.

Random failures may occur due to unfixed operations such as crashes, read/write floppy disks, and printing. Focus on starting from the following circuit signal

(1) system control circuit, such as the ale address lock signal. (2) system memory circuit: Select communication numbers for RAS and CAS columns,

Addrsel row/column address conversion control signal, Memory Data Reading driver, and memory chip speed matching. (3) System

Address Bus and Data Bus chip. (4) Various clock signals of the system: sysclk, pclk, and dmaclk. Note the following:

The speed matching relationship between memory chips and 74fxx, 74 lsxx, and 74alsxx chips. Of course random

When the fault is fixed, you can directly identify the cause of the fault from the phenomenon, such as the host sometimes starts, sometimes does not start,

Once the system works completely normally after startup and remains normal for a long time, it is likely that the "power supply is good" signal power good is not

Normal.

■ 4. Other troubleshooting skills

(1) The motherboard is burned out. It is generally caused by the plug-in the live plugging system, or the power supply in the circuit is short between the ground

In this case, static resistance measurement can be used. If any input/output pin is found to be directly connected to the power supply or (

Except for the original circuit) is a breakdown fault. If the resistance values of two similar input or output feet are found to be very clear

The obvious difference is that, in general, it is also a fault. Note: Do not simply replace the burned-out RMB when the motherboard is burned out for repair.

Check the related components until the short-circuit fault is eliminated and no faulty components are installed.

Try.

(2) the system configuration parameters are incorrect.

Generally, You can reset system configuration parameters for such faults.

When the system configuration parameters can be saved, the battery, cmos ram chip, cmos ram power supply circuit, and read/write circuit should be used.

To find the cause of the fault.

 

More computer knowledge tutorials and computer maintenance knowledge download:

Link: http://t.cn/RP9rtyU computer maintenance internal information

[Computer tutorial] detailed diagram of System Installation Process

Tutorial] computer learning 2.0

[Experience] _ computer repair (you can open your own computer repair shop after reading it !)

4 years experience in computer maintenance

According to these eight items, it is difficult to slow down the computer.

What do every project in Bois mean?

Computer FAQ and fault 1000 Cases

Full-Process Computer Management and Maintenance Diagram

Laptop repair manual

Six commonly used software that damages hard disks for a long time!

Common troubleshooting methods for computer faults

Analysis of common causes of crashes

Computer Fault repair Overview

Analysis of computer crash

Computer Maintenance Skills

Computer Maintenance Training Materials

Computer Repair Quick Start

Computer Maintenance Experience and Maintenance Experience

Apsaravideo for AI

Computer Assembly tutorial

Make your computer faster

Easily eliminate computer faults

System Repair Method 6

Hardware materials and knowledge

View computer configurations

Common hard disk faults

Basic hardware knowledge

How to learn computer repair

Tips and precautions for purchasing host accessories

Self-taught computer repair, familiar with several times you are a master !!!

Latest computer motherboard Fault Diagnosis card query table

Motherboard repair full learning Manual