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Introduction

Diagnostic software is extremely necessary if the system starts to fail or if you upgrade it by adding new devices. Even when you are trying to perform a simple operation (for example, to install a new board) or are looking for a malfunction in the hardware that caused the system to crash or freeze, you need to know more about the computer than is written in the instructions attached to it. Diagnostic programs allow you to check the operation of the entire system, as well as its individual nodes. Naturally, regular maintenance is necessary when operating the menu system. This is what is the key to the normal operation of the computer.

Maintenance and repair (maintenance and repair, maintenance and repair - maintenance and repair) - a set of operations to maintain the health or health of production equipment (products, parts) in the course of technical operation, storage and transportation.

Maintenance - preventive measures that are carried out systematically, forcibly after set periods, including a specific set of activities.

In computer terminology, the term "periphery" unites all PC devices, except for the processor and RAM. There are other terms for these devices, for example, "data input / output devices", "additional devices", etc.

Периферийные устройства персонального компьютера - это клавиатура, манипулятор «мышь», монитор, принтер, жесткий диск, привод CD-/DVD- дисков, модем, сетевая карта (для подключения к сети Интернет), видеокамера, сканер и т.п.

1. PC Diagnostics

1.1 Diagnostic programs

For PC, there are several types of diagnostic programs (some of them are supplied with the computer), which allow the user to identify the causes of problems that occur in the computer. In many cases, such programs can do most of the work of identifying a defective node. Conventionally, they can be divided into several groups, presented below in order of increasing the complexity of programs and expanding their capabilities. POST (Power-On Self Test - procedure for self-test when you turn on). Runs every time you turn on the computer. Manufacturers diagnostic programs. Most well-known computer manufacturers (IBM, Compaq, Hewlett-Packard, Dell, etc.) produce specialized diagnostic software for their systems, which usually contains a set of tests that allow you to thoroughly check all computer components. Diagnostic programs supplied with peripherals. Many equipment manufacturers produce diagnostic programs designed to test a specific device. For example, the company Adaptec releases programs to test the performance of SCSI adapters.

Diagnostic programs of operating systems. Windows 9x and Windows NT / 2000 / XP come with several diagnostic programs for checking various computer components. General-purpose diagnostic programs. Such programs, which provide thorough testing of any PC-compatible computers, are produced by many companies.

Power On Self Test (POST), a sequence of short routines stored in ROM BIOS on the motherboard. They are designed to check the main components of the system immediately after it is turned on, which is the reason for the delay before the operating system is loaded.

1.2 Test object

Each time the computer is turned on, it automatically checks its main components: processor, ROM chip, auxiliary elements of the motherboard, main memory, and main peripheral devices. If a faulty component is detected, a warning or error message (malfunction) is issued. Although the diagnostics performed by the POST program are not completely complete, it is the first “line of defense”, especially if serious faults are detected in the motherboard. If it turns out that the problem is serious enough, the further loading of the system will be suspended and an error (malfunction) message will appear, which, as a rule, can determine the cause of its occurrence (fatal errors ¬ fatal error). The POST procedure usually involves three ways to indicate a fault.

  1. Sound signal. To do this, use the sound speaker connected to the motherboard.
  2. POST control codes. Hexadecimal control codes sent to the address of the port I / o. To view the codes, you need to install a special adapter in the ISA or PCI slot.
  3. Screen messages. Error messages are displayed on the monitor after the initialization of the video adapter. Audio error codes issued by the POST procedure. When a POST procedure detects a malfunction, the computer emits characteristic sound signals by which it is possible to identify the faulty element (or their group). If the computer is healthy, when you turn it on you will hear one short beep; if a fault is found, a whole series of short or long beeps is generated, and sometimes a combination of them. The nature of the sound codes depends on the version of the BIOS and the company that developed it.

Error codes issued by the POST procedure to the I / O ports. A less well-known feature of this procedure is that at the beginning of each test, the address of the special I / O port POST issues test codes that can only be read using the adapter's special board installed in the expansion slot. Some companies (Micro 2000, JDR Microdevices, Data Depot, Ultra-X, Quarterdeck, Trinitech, etc.) produce such cards for professionals involved in the service of computers. POST board is installed in the expansion slot. At the time of the POST procedure, two digit hexadecimal numbers will quickly change on its built-in indicator. If the computer suddenly stops testing or “freezes”, this indicator will display the code of the test during which it failed. This allows us to significantly narrow the search for a faulty item. Many older POST adapters were plugged into an 8-bit connector, which is part of the ISA / EISA standard. Many systems (even with PCI slots) still support the ISA interface.

Currently, PCI adapters are widely available. For example, Micro 2000 releases the Post-Probe adapter, equipped with both an ISA connector and a PCI. In turn, the PCWiz company releases a similar PCISA FlipPOST board. Both manufacturers also support the MCA (Micro Channel Architecture) bus used in older IBM PS / 2 systems. Screen messages BIOS POST Screen messages briefly indicate a possible problem, and only after the video adapter and monitor are initialized by the system.

Different types of messages depend on the specific BIOS version and often differ for different BIOS from the same manufacturer. The BIOS error message codes are provided on the enclosed CD. Most BIOS test boards come with documentation that describes POST codes for different BIOS versions. Error messages of RAM in most PC-compatible models, the POST procedure displays on-screen testing of the computer’s RAM. The last displayed number corresponds to the amount of memory successfully passed the test. So, the following message may appear: 32768 KB OK

In general, the last number displayed during testing should coincide with the volume of the entire memory installed in the computer (both main and extended). However, some computers may display a slightly smaller value. If at the end of the test the number on the screen does not correspond to the total amount of memory, then an error has been detected in the system memory. If a fault is detected during the POST procedure, a corresponding message is displayed on the screen, usually in the form of a numeric code of several digits. Using the operating and service manual, you can determine which fault corresponds to this code.

1.3 Hardware Diagnostics

Many types of diagnostic programs are designed for certain types of hardware. These programs come with devices.

Diagnosing SCSI devices Most SCSI adapters have a built-in BIOS with which you can configure the adapter and perform its diagnostics. In some cases, the SCSI BIOS contains special configuration and diagnostic software. Adaptec is the most popular manufacturer of SCSI host adapters, which include an adjustable BIOS. When the BIOS is activated, a message appears on the monitor when the system boots, indicating the adapter model and BIOS number and prompts to press the key combination to run the SCSISelect utility. This utility identifies the Adaptec host adapters installed in the system and allows you to select the correct adapter to work by determining the port address. After this, the menu of functions integrated in the BIOS of the adapter will appear. Each BIOS contains a configuration program and a SCSI Disk Utilities function that scans the SCSI bus and identifies the devices connected to it. For each hard drive connected to the bus, you can carry out a non-level formatting or scanning to locate and convert defective data blocks. For SCSI adapters that use direct memory access (DMA) technology, the host adapter diagnostics feature is useful when it checks the connection between the adapter and the main system dataset using DMA transactions. If the test fails, instructions are given to the user for using a lower DMA transfer rate.

1.4 Network Adapter Diagnostics

Like SCSI adapters, many network interface cards are equipped with a diagnostic system that allows you to check your own specialized functions. The EZSTART program, supplied with all SMC network adapters, includes two test modes. The basic mode allows the following internal tests of the SMC8000 adapter: network interface controller; addressing ROM (ROM) local network; Ram; ROM; feedback; interrupt generation

The serial communication test of two nodes requires another node on the same network with an SMC adapter installed. When you run EZSTART on both systems, one computer is configured as a receiver, and the second as a transmitter. The transmitter transmits test messages to the receiver, which reflects the same messages back. If the adapters and the network as a whole are functioning normally, the messages should return to the transmitter in exactly the same form and order as they were sent. Other network adapters have similar test functions, although the names of diagnostic methods may differ.

The program for the network adapter 3Com 3C509B, for example, allows you to perform the following tests: access to the system registry; EEPROM data; EEPROM configuration data; FIFO feedback; interrupts; Ethernet Ethernet Feedback; encoder / decoder feedback; echo exchange (requires two adapters on the same network).

Some network card manufacturers, such as SMC and 3COM, also offer diagnostic software. These programs can be found on a diskette or CD-ROM that comes with the device, or go to the manufacturer's website.

1.5 General Diagnostic Programs

There are many different diagnostic programs for PC-compatible computers. These are special programs for testing memory, hard drives, floppy drives, video adapters and other system components.

1.6 Hardware Diagnostics

In most cases, it is impractical to acquire a diagnostic program, since the system can be tested with existing operating system tools. There are several diagnostic programs in Windows 95/98 / Me / NT / 2000.

The term boot (boot) comes from the English bootstrap (bootstrap, self-promotion) and means the beginning of the personal computer. A large operating system boots into the computer, but it all starts with a small program that then "pulls" everything else. Sometimes when you boot the system, a program error message appears. If the error message is displayed by a specific program, therefore, this program is loaded and partially running. Studying the boot sequence allows you to determine the service or program that prevents the execution of the boot procedure. Pay attention to the files or disk areas involved during the download. Below are the programs that can display a message during the boot process, independent of the operating system: ROM BIOS on the motherboard; optional ROM BIOS adapters; master boot record (MBR); boot sector of the active partition. The initial stage of loading is performed on all computers equally and does not depend on the installed operating system. Further actions depend on the type of operating system installed.

2. Review of research and development

Load: the initial stage, regardless of the type of operating system installed. If you have problems booting your computer, try to determine at what point it happened. The process of standard computer boot can be divided into a number of stages.

  1. Power on the computer.
  2. The power source performs a self test. Between turning on the computer and the signal goes 0.1-0.5 s.
  3. The timer chip receives a Power_Good signal and stops generating a Reset signal sent to the processor.
  4. The processor starts to execute the code recorded in the ROM BIOS at the address FFFF: 0000. The size of the ROM BIOS from this address to the end is 16 bytes; At this address, a transition command is written to the actual executable ROM BIOS code.
  5. ROM BIOS performs a system test to test its performance. Upon detecting an error, the system will beep, as the video adapter is still not initialized.
  6. Plug and Play BIOS checks for persistent I / O addresses, interrupt lines, DMA channels, and other parameters.
  7. All Plug and Play devices listed in the Plug and Play BIOS are deactivated.
  8. A map of used and free resources is created.
  9. Plug and Play devices are configured and activated. If your computer has a non-Plug and Play BIOS installed, Plug and Play devices are initialized based on the default settings.
  10. When searching for a video adapter program, the BIOS scans the video memory addresses of the video adapter, starting with C000: 0000 and ending with C780: 0000. If the video adapter BIOS is found, then if the checksum matches the preset, the video adapter BIOS is passed and displays the cursor; otherwise, the message C000 ROM Error appears.
  11. If the video adapter's BIOS is not found, the video driver written in the motherboard ROM chip is used, which initializes the video adapter and displays the cursor on the screen.
  12. The motherboard BIOS scans the remaining memory from C800: 0000 to DF80: 0000 in 2-Kbyte increments in search of the BIOS for any other adapters connected to the system board (such as SCSI adapters).
  13. If the BIOS checksum does not match, the message XXXX ROM Error is displayed, where XXXX is the segment address of the incorrect ROM module.
  14. The BIOS checks the value of the word at address 0000: 0472 to determine which boot is being performed: hot-word 1234h, which leads to the omission of POST (Power On Self Test — self-test at power-up).
  15. In the case of cold boot, POST is performed: a message is displayed on the computer screen about all errors that occur and a signal is given. Upon successful completion of POST, a single beep sounds.
  16. The BIOS searches the drive A for a system diskette and reads sector 1 on cylinder 0, side 0 (the very first sector), and also from other devices (hard disk and CD-ROM) on it. This sector is loaded at address 0000: 7C00 and checks whether the disk is bootable.
  17. If the values ??of the first bytes of the read sector are incorrect, a boot record error message of the floppy disk 602-Diskette Boot Record Error is displayed on the screen and the system stops.
  18. If the diskette was prepared in DOS using the Format command or Sys, and the first two files in the root directory are not system files, a message is displayed stating that the disk is not system.
  19. If there is no system diskette in drive A, the BIOS reads the MBR sector (Master Boot Record is the master boot record); this is the very first sector on the hard disk (located at the same physical address as the boot sector on the diskette). Having detected such a sector, the BIOS loads it into memory at 0000: 7C00 and then checks it.
  20. If the last two bytes of this sector (its signature) are not equal to 55AAh, interrupt 18h is triggered, a message appears on the screen (depends on the manufacturer). The master boot record (MBR) sector is written to the hard disk by the FDISK program. Error messages will be issued if you formatted the drive at a low level, but forgot to split it into partitions (logical drives).
  21. The boot loader searches the partition table for the active partition.
  22. If there is no active partition in the table, an error message is displayed by calling the software interrupt 18h BIOS.
  23. If at least one partition contains an incorrect label or several partitions are marked as active, an Invalid partition table error message is displayed and the system stops.
  24. The signature of the read boot sector of the active partition is checked. If the last two bytes do not match the 55AAh signature, a Missing operating system error message is displayed and the system stops.
  25. The boot sector of the active partition, as its name implies, contains the operating system boot program. If the boot sector is corrupted, the system files are not the first in the root directory, or there are failures when you try to read them, a message is displayed (see step 18).

3. Tools and devices

To search for small faults and repair PCs, it is enough to have only a few basic tools or special tools that allow you to identify problems and fix them simply and quickly. These include: a simple set of tools for disassembly and assembly; diagnostic devices and programs for testing computer components; instruments for measuring voltage and resistance: a digital multimeter, logic probes and single pulse generators for testing digital circuits; chemicals (contact wiping solution), a spray with a coolant and a can of compressed gas (air) for cleaning computer parts; a set of tampons for wiping contacts; specialized tools at hand (for example, tools needed to replace chips (chips); test connectors for testing serial and parallel ports; memory test instruments for evaluating the performance of SIMM / DIMM / RIMM modules; network cable scanner ( when working with PCs connected to the network).

In some cases, soldering tools may be required. The listed tools and accessories are discussed in this section.

3.1 Improvised tools

Strangely enough, the tools necessary for servicing almost all computers are relatively simple and inexpensive. Most of them can easily fit in a small bag or box. The cost of accessories for computer maintenance ranges from $ 20 (for a small service kit) to $ 500 (for a luxury professional kit). The inexpensive kit includes the following tools.

3.2 Types of fasteners

IBM uses such screws in its PC, XT and AT; they are also used in most compatible computers. Screwdrivers of various sizes for these screws are designated as: T-8, T-9, T-10, T-15, T-20, T25, T-30, T-40, etc. The type of Torx screws are secret screws, used in power supplies and some nodes: they look like ordinary screws of this type, but they have a pin in the center of the slot. They require a special screwdriver.

The only way to do this without an appropriate screwdriver is to carefully cut off the pin with a small chisel.

Computer fasteners can be of two types - inch and metric. IBM uses inch fasteners for most of its computers, but many manufacturers use metric screws and nuts. Most often, this has to be faced when replacing drives. Today, manufacturers of most types of drives mainly use the metric standard.

Some screws (especially used for mounting drives on hard drives) must have a strictly fixed length. If you have doubts, try to find the documentation - it says exactly what screws are needed for fastening and what should be their length.

4. Measuring instruments

Sometimes when checking circuit boards or components, one has to use measuring devices and special devices. They are relatively inexpensive and easy to use. To test your computer you need a multimeter and test connectors. Using a multimeter, you can measure various parameters, such as voltage at different points in the circuit or at the output of the power supply, and check for a broken conductor on the circuit board or cable. Test connectors allow you to check the serial and parallel ports and cables connected to them. A good addition can serve as a tester of the power outlet, with which they verify the correctness of the network wiring to the outlet.

4.1 Measuring instruments

When troubleshooting digital circuits, it is convenient to use a logic probe. The digital signal can be either high (5 V) or low (0 V) level. The pulses are very short (fractions of a microsecond), and their frequency can reach tens of megahertz, so an ordinary multimeter is useless in this situation. The logic probe is designed to monitor and display just such digital signals. Especially it can be useful when troubleshooting in the "dead" computer. Using the probe, you can check the operation of the clock generator and the presence of other synchronization signals. You can compare the signals at each end of an integrated circuit with the signals on a working chip and find the failed component.

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