what is troubleshooting

what is troubleshooting

PC is a modular device. Its components are easily separable. This makes the troubleshooting easier. Most of the troubleshooting is just defect the faulty device and replaces with a good one. Among all the troubleshooting ways, there are some rules.

Troubleshooting Approaches

Microcomputer system has three main components. Any problem to troubleshoot may come from any of the three sides. The main components are:
♦ Hardware
♦ Software
♦ Human ware.

The main steps to troubleshoot a microcomputer are:

♦ Identify the source of the problem: Here the cause of the problem i.e., the faulty component (any component of hardware, software or human ware) is detected.
♦ Troubleshoot the problem: Here the problem is removed by repairing or replacing the faulty component.

Two Approaches for Fault Detection

The most important job of troubleshooting is finding the source of the problem. After detecting the faulty device, the rest of the work is very simple: just try to repair the faulty device and if repairing is very difficult or impossible, then replace the device with a good one. There are two main approaches to detect the faulty device.

Hardware Approach
 
Hardware generally refers to the machine or physical equipment that performs the basic functions of the data processing cycle. In addition to the computer itself, other hardware devices are also required. These devices may be off-line that is detached from the computer and operating independently or they may be on-line that is directly connected to and controlled by the computer. A printer is an off line device and a keyboard is an on-line device.

When hardware is used as the tool for fault detection, then this approach is called hardware approach. For example, one way of the hardware approaches for troubleshooting may be:

♦ Separate probable faulty devices from the troubling PC.
♦ Install each of the devices in a well-running PC.
♦ If the well-running PC shows trouble for any of the probable faulty devices, then the troubling device in the well-running PC is the faulty one.

As the well-running PC is used here as the fault-detecting tool, this approach is hardware approach.

Software Approach
 
A program is a sequence of instructions, which directs a computer to perform certain functions. A computer must have access to prewritten, stored programs to input and store data, make decisions, arithmetically manipulate and output data in the correct sequence. Programs are referred to as software. Computer system must be supported by extensive software systems.

When software is used as the tool for fault detection, then this approach is called software approach. For example, one way of software approach for troubleshooting is using the diagnostics software. Different ways of software approaches will be discussed later.

General Troubleshooting Rules

Some general rules should be followed during troubleshooting. These are:
♦ Do not panic. Have confidence
♦ Keep note of important troubles and solves
♦ Reboot the PC
♦ Simplify the PC configuration
♦ Think out a line to troubleshoot
♦ Go to the easiest way first.

Have Confidence

You should have self-confidence about troubleshooting. If you have never opened a PC before, there’s no problem. To learn troubleshooting you have to open the PC. And nobody can open a PC without opening it first time. I found several of my friends were very much afraid about touching inside the PC. If any time I suggested them, they usually said, “Oh! No! No! That will damage my PC”. But after learning troubleshooting I found one of my friends always keeping his PC casing open. I asked him why he does this. He replied, “I don’t call him a Computer Engineer who keeps his casing closed”.

Keep Note

You should preserve a note of each troubleshooting problem and how it was solved. Then you will be able to solve easily when you fall again in the problem. This writing would be possible to do if you always keep a notebook with yourself during troubleshooting. But if the problem is very easy to solve and you think that you will not forget it later then you need not write this. It is very much essential to keep a note and a diagram during disassembling a PC. It is further discussed in the lesson: 7 of this unit.

Reboot the PC

Rebooting the PC refreshes the PC components and solves many problems. For example, a voltage transient (high voltage with smaller than 10-3 sec duration) may change the data in several bytes of RAM and your computer locks up. Rebooting can solve this problem. But it is not safe to immediately reboot in operating systems like Windows, NT and OS/2. At first the running applications should be closed. Then follow the steps suggested by the operating system developers to shut down.

Simplify the PC Configuration

A PC normally has many driver programs and software for:

♦ Sound card
♦ Network card
♦ Video card
♦ Mouse
♦ Screen saver
♦ Printer
♦ Scanner
♦ Modem
♦ Applications.

Disabling some of the drivers and software you simplify the PC configuration. PC configuration means the list of active devices (hardware and software) in the PC.

In DOS 6.xx, you can simplify the configuration as follows:
♦ Reboot the PC.
♦ When the message ‘Starting MS – DOS…” appears press <F5>.

Then CONFIG.SYS and AUTOEXEC.BAT are skipped and your PC boots with simplified configuration.

In Windows 95, you can simplify the configuration as follows:

♦ Reboot the PC.
♦ When the message ‘’Starting Windows…” appears press <F8>.
♦ A menu appears. Select ‘Safe mode’ from the menu.

Think out a Line to Troubleshoot

Every component of a PC is attached to one another. So a fault in one device implies a fault not only in that device, but also in the devices attached to it, and the devices attached to the devices attached to it. For example,

♦ A printer is attached with the printer cable.
♦ The cable is attached with the printer port.
♦ The printer port is attached with the motherboard.
♦ The motherboard is attached with the software.

So a problem in printing may be caused by a fault in any (or some) of the following:
♦ The printer
♦ The printer cable
♦ The printer port
♦ The motherboard
♦ The printing software

But not for a fault in the mouse. To troubleshoot the printing problem you have to do:

♦ Separate each of the five components from the PC
♦ Install each component in a well-running PC to check if it is faulty. Thus the faulty component is detected.
♦ Try to remove the fault in the detected faulty component.
♦ If you failed to remove the fault, replace the faulty component with a good one.

Go to the Easiest Way First

If you think that the trouble is in one of several components then check the easiest one first. For example, you have found that the display is not working properly. This may happen for the fault in one (or some) of several components:

♦ The monitor
♦ The cable
♦ The video card
♦ The motherboard.

To detect the faulty component you have to replace each of the four components one by one. But which should be replaced first? The cable, because it is the easiest to replace.

Troubleshooting Steps

The following steps should be followed for a successful troubleshooting.

♦ Check if the operator has mistaken
♦ Check if all the devices are plugged correctly
♦ Check if any new change is done
♦ Check the software
♦ Check external symptoms
♦ Use diagnostic programs
♦ Disassemble the PC, clean the connectors and reassemble.

Check if the Operator has Mistaken

Many problems are created only for the ignorance of the operator of how to use the computer. So when a program is not working, at first check if the operator uses the program in the proper way. The language of computer confuses people. For example, you may have seen the prompt “Press any key to continue…” many times. Many new users can not understand what does the “any key” means. They look on the keyboard and become puzzled not finding any key named “any key”.

I have heard the story of a computer user. One day he saw the prompt “Insert ‘System Disk 1’ in drive A: and close the door”. He inserted the disk in drive and then closed the office door. Another new user thought the mouse a pedal. He complained that he is pushing the pedal but it is not working.

From many clients, you will get complains like, “I’m doing what the manual says but the computer doesn’t work”. Most often they are not lying. Because after troubleshooting you will find that the fault is not in the computer or in the manual. The fault is in their understanding the manual.

Check if all the Devices are Plugged Correctly Many problems are happened because of improper connection.

Improper connection means:

♦ A connection is not done.
♦ A connection is done but it becomes loose.
♦ A connection is done and it is not loose but it is done in wrong direction.

So, check if all the external connections are plugged tightly with proper direction.

One day I found that a PC was not working though it was working little moment before. I checked all the connections and they were plugged `properly. AT last I found that the PC is plugged in the voltage stabilizer and the stabilizer is connected in the wall socket properly but the stabilizer is off.

Check if any New Change is Done

If the PC was working properly before some time and now it is making trouble, then check if any change has been made between this period. This change may be responsible for the problem. So undoing the change will remove the problem.

For example, some early PC programs like ‘Infocom’ games do not run in more than 512K RAM. If you add some RAM after 512KB then Infocom game will prompt “Illegal operation” and reboot the PC. From this prompt it is not possible for you to find out the fault. By ‘checking if any new thing is done’ you will find that before adding the RAM the game was working properly, but after adding it fails. So the problem is in RAM addition.

To ‘check if any new thing is done’ you should check:

♦ Any new hardware added
♦ Any hardware setup changed
♦ Any new software added
♦ Any software setup changed.

Checking Software and Symptoms

Check the Software

Most of the microcomputer problems are software problems. A separate book can be written on troubleshooting one software.

(For example, Windows, NT, OS/2, LINUX etc.) Software problems have several causes:
♦ Operator’s fault
♦ Bug in the device driver
♦ Bug in the software
♦ Virus.

Operator’s Fault

Many problems are created only for the ignorance of the operator of how to use the computer. So when a program is not working, at first check if the operator uses the program in the proper way.

Bug in the Device Driver

Device driver is the software that is used to drive specific device.They support the operating system. If the device driver has a bug or not installed properly, then it will not do its job correctly.

For example, in Windows 98 environment the device driver for printer ‘HP LaserJet 4L’ drives the ‘HP LaserJet 4L’ printer. When any application wants to print a document:

♦ The application supplies printing request to the Windows 98.
♦ If the attached printer is ‘HP LaserJet 4L’,
Windows 98 delivers the printing request to the device driver software for ‘HP LaserJet 4L’.

♦ The device driver performs most of controlling of the ‘HP LaserJet 4L’ printer and delivers the printing request to the printer.

The printer prints the document as ordered by the device driver.

If there is a bug in the device driver for ‘HP LaserJet 4L’ or it is not installed properly then it will not be able to print the document. Just reinstalling solves most of the device driver problems.

Bug in the Software

The bug in the software is the source of many PC troubles. Much popular software do not work properly in the situation of insufficient memory, full disk or some other situation that the developer did not consider. The solution of software bug is not in the user’s hand. He can just inform the manufacturers and the coworkers in his company.

Virus

Viruses are special programs. They have following characteristics:

♦ These are very small programs
♦ They hide themselves
♦ Make disturbance to computer users
♦ They can make new copies and distribute these copies to other computer.

Virus can be removed by running anti-virus software. Different popular antivirus software are TOOLKIT, Norton Anti Virus, McAffee Anti Virus etc.

Check External Symptoms

A faulty device may show some symptoms. By checking any abnormal behavior you can detect the source of trouble. One important thing in troubleshooting is detecting the faulty component. External symptoms can help here. Example symptoms are:

♦ The floppy disk light is continuously on
♦ The hard sounds too much
♦ The monitor image becomes bent
♦ Some peripheral device hums

Using Post and After Boot Diagnostics Software

Introduction
 
Diagnostic programs are used to detect PC problems. Different types of diagnostics programs are:

♦ The power on self test (POST)
♦ After boot diagnostics software
♦ ROM based diagnostics tools.
Some components of the PC should run to run the diagnostics software. These are:
♦ The motherboard (including CPU and RAM). Because if they do not run, no other devices will run
♦ The monitor and the video card should run interact with the user.
♦ The keyboard should run to get user input
♦ The floppy drive should run to load the program.

The Power on Self Test (POST)

Every time the PC is powered-on this program is run. It checks if the basic hardware (CPU, RAM etc.) exists and tests the memory. The checking done by IBM PC-1 BIOS is discussed here.

Checking done by other BIOS is nearly similar. POST in IBM PC-1 BIOS checks the following things sequentially:

♦ CPU registers and flags. If faulty then halts.
♦ ROM checksum. If faulty then halts.
♦ DMA controller. If faulty then halts.
♦ Interrupt controller. If faulty then POST makes a long beep and a short beep and then halts.
♦ Timer and its speed. If faulty then POST makes a long beep and a short beep and then halts.
♦ BASIC ROM. If faulty then makes a long beep and a short beep and then halts.

♦ Video controller. If faulty then it makes a long beep and a short beep and then halts.
♦ Installed adapters. If okay then let them (the adapters) initialize.
♦ CRT Interface lines. If okay then blinks the cursor.
♦ All system RAM.
♦ Keyboard. If faulty then makes a short beep but does not halt.
♦ Cassette interface. If faulty then makes a short beep but does not halt.
♦ Diskette adapter and drive ‘A:’. If faulty then makes a short beep but does not halt.
♦ Determines how many printers, serial ports and game ports are connected. Then makes a short beep and starts booting.

After Boot Diagnostics Software

We have many diagnostics software as application package. They are run after the booting of the operating system. They can be used for the following functions:

♦ Making a list of active devices
♦ Run the PC continuously
♦ Finding addresses of interrupt, DMA, I/O etc.
♦ Initialize some devices.

Several diagnostics packages are Chekit, QAPlus, PC-Technitian, Displaymate, SpinRite etc.

Listing Active Devices

These programs detect and display a list of all active devices in a computer. Using these diagnostics software, many problems can be detected. For example, you have installed a LAN card in your computer, but the list does not show any LAN card. Then you can say that, the LAN card or the device driver of the LAN card has some problem.

Run the PC Continuously

Some problems can not be detected if the PC does not run continuously for several days. Simple diagnostics programs are not sufficient for this purpose because the need many user inputs different times to perform a job. Special diagnostics packages are available which do not need any intermediate user response for continuous operating. They keep an error-log file and print all the errors happened between this long running period.

Finding Address Mapping

Some troubles are happened for interrupt, DMA or I/O address conflict. For example, if two expansion boards are configured to use the same interrupt address, none of them will work properly. Using some diagnostics software, the interrupt address used by the boards can be displayed and any interrupt conflict can be detected.

Initialize Some Devices

Some diagnostics packages are used to initialize some devices. For example, many packages are available to partition and format the hard disks or performing low level format on the older hard disks.

Using ROM Based Diagnostics Software

ROM Based Diagnostics Tools

It is a small circuit board containing a ROM and some other electronics. It is installed in the motherboard by replacing the BIOS ROM. It allows booting and checks the chips separately. In this ROM based diagnostics software, another card with some LED is inserted in the expansion slot of the motherboard. For a specific fault, the set of LED glows in a specific way. By observing the on/off positions of the LED, the fault is detected.

These ROM based diagnostics software needs no running monitor, floppy drive or keyboard. Just need the following devices running (running means, it is not necessary that they are completely okay, they may have slight problems but they can run):

♦ CPU
♦ Motherboard
♦ RAM
♦ Power supply unit.

IBM Error Code Table

The POST and some ROM based diagnostics tools inform about the detected fault by emitting sound and displaying number. Many of them use the IBM error code table for this purpose.

01x Undetermined problem errors
02x Power supply errors
1xx System board errors
101 Interrupt failure
102 Timer failure
103 Timer interrupt failure
104 Protected mode failure
105 Last 8042 command not accepted
106 Converting logic test
107 Hot NMI test
108 Timer bus test
109 Direct Memory Access test error
121 Unexpected hardware interrupts occurred
131 Cassette wrap test failed
161 AT battery failure
162 AT setup into incorrect (rerun SETUP)
163 Time and date not set (run SETUP)
164 Memory size error (run SETUP)
165 PS/2 does not know how to configure board
199 User indicated configuration not correct
2xx Main memory (RAM) errors
201 Memory test failed
202 Memory address error
203 Memory address error
3xx Keyboard errors
301 Keyboard error. If followed by a number the number is
the scan code of the key in question.
302 User indicated error from keyboard test or AT key lock
locked
303 Keyboard or system unit error
304 CMOS does not match system
4xx Monochrome monitor errors
401 Adapter memory, horizontal sync frequency test, or
video test failed
408 User indicated display attributes failure
416 User indicated character set failure
424 User indicated 8O x 25 mode failure
432 Parallel port test failed
5xx Color monitor errors
501 Color adapter memory, horizontal sync frequency test
508 User indicated display attributes failure
516 User indicated character set failure
524 User indicated 80 x 25 mode failure
532 User indicated 40 x 25 mode failure
540 User indicated 320 x 200 mode failure
548 User indicated 640 x 200 mode failure
6xx Diskette drive/controller failures
601 Adapter or drive failed POST
602 Diskette test failed: boot record is not valid
606 Diskette verify function failed
607 Write-protected diskette
608 Bad command diskette status returned
610 Diskette initialize failed
611 Timeout
612 Bad NEC chip on diskette controller
613 Adapter failed DMA test
621 Bad seek
622 Bad CRC found
623 Record not found
624 Bad address mark
625 Bad NEC seek
626 Diskette data compare error
7xx 8087 or 80287 math coprocessor errors
9xx Printer adapter errors
1101 Asynchronous (RS232) adapter failure (C0M1)
1201 Asynchronous (R5232) adapter failure (COM1)
13xx Game port failure
1301 Adapter test failed
1302 Joystick test failed
14xx Printer errors
1401 Printer test failed
1402 Dot matrix printer test failed
15xx SDLC adapter (mainframe connection) failure
1510 Failure of 8255 port B
1511 Failure of 8255 port A
1512 Failure of 8255 port C
1513 8253 timer 1 did not reach terminal count
1514 8253 timer 1 stuck on
1515 8253 timer 0 did not reach terminal count
1516 8253 timer 0 stuck on
1517 8253 timer 2 did not reach terminal count
1518 8253 timer 2 stuck on
1519 8273 port B error
1520 6273 port A error
1521 8273 command/read timeout
1522 Interrupt level 4 failure
1523 Ring indicate stuck on
508 User indicated display attributes failure
516 User indicated character set failure
524 User indicated 80 x 25 mode failure
532 User indicated 40 x 25 mode failure
540 User indicated 320 x 200 mode failure
548 User indicated 640 x 200 mode failure
6xx Diskette drive/controller failures
601 Adapter or drive failed POST
602 Diskette test failed: boot record is not valid
606 Diskette verify function failed
607 Write-protected diskette
608 Bad command diskette status returned
610 Diskette initialize failed
611 Timeout
612 Bad NEC chip on diskette controller
613 Adapter failed DMA test
621 Bad seek
622 Bad CRC found
623 Record not found
624 Bad address mark
625 Bad NEC seek
626 Diskette data compare error
7xx 8087 or 80287 math coprocessor errors
9xx Printer adapter errors
1101 Asynchronous (RS232) adapter failure (C0M1)
1201 Asynchronous (R5232) adapter failure (COM1)
13xx Game port failure
1301 Adapter test failed
1302 Joystick test failed
14xx Printer errors
1401 Printer test failed
1402 Dot matrix printer test failed
15xx SDLC adapter (mainframe connection) failure
1510 Failure of 8255 port B
1511 Failure of 8255 port A
1512 Failure of 8255 port C
1513 8253 timer 1 did not reach terminal count
1514 8253 timer 1 stuck on
1515 8253 timer 0 did not reach terminal count
1516 8253 timer 0 stuck on
1517 8253 timer 2 did not reach terminal count
1518 8253 timer 2 stuck on
1519 8273 port B error
1520 6273 port A error
1521 8273 command/read timeout
1522 Interrupt level 4 failure
1523 Ring indicate stuck on
1524 Receive clock stuck on
1525 Transmit clock stuck on
1526 Test indicate stuck on
1527 Ring indicate not on
1528 Transmit clock not on
1531 Data Set Ready not on
1532 Carrier Detect not on
1533 Clear to Send not on
1534 Data Set Ready not on
1536 Clear to Send stuck on
1537 Level 3 interrupt failure
1538 Receive interrupt results error
1539 Wrap data miscompare
1540 DMA channel 1 error
1541 Error in 8273 error check or status reporting
1547 Stray interrupt level 4
1548 Stray interrupt level 3
1549 Interrupt presentation sequence timeout
16xx Terminal emulation errors (32xx, 5520, 525x)
17xx Hard disk/disk controller errors
1701 POST error
1702 Adapter failure
1703 Drive failure
1704 Drive or adapter failure: can not be determined
1780 Drive 0 failure (drive C:)
1781 Drive 1 failure (drive D:)
1782 Adapter failure
1790 Drive 0 failure (couldn't read the LAST
cylinder-probably misspecified drive)
1791 Drive 1 failure
18xx Expansion Chassis failures
1801 POST error code
1810 Extender card failure
1811 Extender card failure
1812 Address or wait state failure
1813 Address or wait state failure
1816 Extender card failure
1819 Wait request switch set incorrectly
1820 Receive card failure
1821 Receiver card failure
19xx 3270 PC communications controller failures
20xx BSC adapter (mainframe connection) failures
2010 Failure of 8255 port B
2011 Failure of 8255 port A
2012 Failure of 8255 port C
2013 8253 timer 1 did not reach terminal count
2014 8253 timer 1 stuck on
2015 8253 timer 0 did not reach terminal count
2016 8253 timer 0 stuck on ·
2017 8253 timer 2 did not reach terminal count
2018 8253 timer 2 stuck on
2019 8273 port B error
2020 8273 port A error
2021 8273 command/read timeout
2022 Interrupt level 4 failure
2023 Ring indicate stuck on
2024 Receive clock stuck on
2025 Transmit clock stuck on
2026 Test indicate stuck on
2027 Ring indicate not on
2028 Receive clock not on
2029 Transmit clock not on
2030 Test indicate not on
2031 Data Set Ready not on
2032 Carrier Detect not on
2033 Clear to Send not on
2034 Data Set Ready not on
2036 Clear to Send stuck on
2037 Level 3 interrupt failure
2038 Receive interrupt results error
2039 Wrap data miscompare
2040 DMA channel 1 error
2041 Error in 8273 error check or status reporting
2047 Stray interrupt level 4
2048 Stray interrupt level 3
2049 Interrupt presentation sequence time out
21xx Alternate BSC adapter failures
2110-49 (Same as above, but with 21 prefix rather than 20)
2201 PC wiring cluster adapter failure
2401 EGA/VGA failure: may show text
2901 Color dot matrix failures
330t Compact printer failures
86xx Mouse error

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