Home Computer Hardware II Process of Fault diagnosis

Process of Fault diagnosis

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Before getting into the troubleshooting details, it is important to know about what goes on during the startup process. The reason is, there are actually quite a few steps that occur in between switching the power ON and hearing the familiar Windows 95, 98 or Windows ME./XP startup sounds and seeing the Windows desktop. In fact, there are a whole series of files that are automatically loaded one after the other when you turn your computer on. The trick with troubleshooting startup problems is trying to figure out which of those files (or what step in the process) causes a specific problem in the computer. If we know approximately where in the startup process the problem occurs (Computer gets stuck), we can diagnose the problem easily.

This chapter explains the various problems that occur in a computer and the troubleshooting procedures. 


When your computer is first turned on, it automatically loads a program called the BIOS, or Basic Input/Output System, which is stored on a special chip on your computer’s motherboard. The BIOS is essentially a combination of software and hardware in that it consists of software, but the contents of that software is stored in a hardware chip.

One of the first things we should see on your computer’s monitor when we start the PC is some type of message like “Hit Esc to enter Setup,” although instead of Esc it may say F2 or F10 or any number of other keys and instead of Setup it may say CMOS Setup or BIOS Setup or just CMOS. Make note of the key required to enter the Setup program because we may need that later (some startup problems can only be solved by changing some BIOS/CMOS settings via the Setup program).

Power-On Self Test (POST)

The first thing that the BIOS does when it boots the PC is to perform what is called the Power-On Self-Test, or POST for short. The POST is a built-in diagnostic program that checks the hardware to ensure that everything is present and functioning properly, before the BIOS begins the actual boot. It later continues with additional tests such as the memory test and then it lists any devices that it finds attached to the computer’s internal IDE controller(s). (that is seen on the screen of the monitor) as the boot process is proceeding.

The POST runs very quickly, and you will normally not even noticed that it is happening–unless it finds a problem. You may have encountered a PC that, when turned on, made beeping sounds and then stopped without booting up. That is the POST telling you something is wrong with the machine. The speaker is used because this test happens so early on, before the video is activated! These beep patterns can be used to diagnose many hardware problems  with the PC. The exact patterns depend on the maker of the BIOS; the most common are Award and AMI BIOS.

BIOS Startup Screen

When the system BIOS starts up, you will see its familiar screen display, normally after the video adapter displays its information. These are the contents of a typical BIOS start up screen:

The BIOS Manufacturer and Version Number.

The BIOS Date: The date of the BIOS can be important in helping you determine its capabilities.

Setup Program Key: The key or keys to press to enter the BIOS setup program. (This is usually {Del}, sometimes {F2}, and sometimes another key combination.
System Logo: The logo of the BIOS company, or in some cases the PC maker or motherboard manufacturer.
The “Energy Star” Logo: This distinctive logo is displayed if the BIOS supports the Energy Star standard, which almost all newer ones do.

The BIOS Serial Number: This is normally located at the bottom of the screen. Since BIOSes are highly customized to the particular motherboard, this serial number can be used in many cases to determine the specific motherboard and BIOS version you are using. Check out Wim Bervoets’ BIOS site for a huge list of these numbers

Troubleshooting BIOS Beep Codes

When a problem is identified with the system during the POST, the BIOS will normally produce an error message. However, in some cases the problem is detected so early in the test that the BIOS cannot even access the video card to print the message! In this case the BIOS will produce a beeping pattern on the speaker to tell you what the problem is.

The exact meaning of the beep codes depends on the type and version of BIOS that you have. The three most popular types of BIOS are those made by Award, American Megatrends (AMI) and Phoenix. The beep codes for these BIOS products are described in this part of the troubleshooter. If you are using a PC made by a company that writes its own BIOS, you will have to consult your owner’s manual

A single beep during the boot process, usually right before the BIOS startup screen is displayed, is normal and does not indicate a failure as long as the boot continues on.

Beep codes can be in several different patterns, depending on the BIOS that you are using. Some BIOSes use very simple beep codes in a pattern of varying numbers of short beeps, while others may mix short and long beeps. The Phoenix BIOS is famous for its complicated beep patterns that are actually in up to four groups–one or more beeps and then a pause, followed by as many as three more patterns.

Introduction to Troubleshooting

The problems that occur in a PC can be categorized mainly into two.

  1. Problem of booting or starting up of the PC 
  2. Problem occurring after the boot up. 

For successful troubleshooting, we must always gather some vital information as listed below:
Description of the problem like what error message, unusual displays was seen before the trouble

  1. When did the problem start? 
  2. What was the situation when the problem started ? 
  3. What software or program was running when the problem occurred? 
  4. Was the computer moved in the recent times? 
  5. Was there any electrical power (Mains) supply problem or a thunderstorm prior to the trouble? 
  6. Was any hardware, software or configuration changes made in the computer? 
  7. Has someone else used the computer? 
Next check if the PC is booting or not. If there is any booting problem follow the flowchart shown below to diagnose the fault.  If the screen is blank and entire system is “dead” nor lights, no spinning drive or no fan, then there is obviously power supply problem.

Troubleshooting the power supply

  1. First of all conduct a preliminary check as follows: 
  2. • check for any burnt parts 
  3. Check all connections to the computer like the mains cord, monitor cord are loose and 
  4. ensure that they are well connected. 
  5.  Check if the switches of UPS, Extension cords etc., are switched ON. 
  6. If the fan is not running, turn off the computer, open the case and check the 
  7. connections to the power supply. 
  8. • In newer ATX power supplies, a wire runs from the power switch on the front of the ATX case to the motherboard. Ensure that this wire is connected to the motherboard and the switch turned on before the power comes up. 

Check the output voltage from the power supply. If there is no voltage from the power supply or if there is a low voltage, remove all  non essential expansion cards (modem, sound etc.,) and check the voltage. 

If there is no voltage still then the power supply unit is faulty.
If the voltage is OK after all the cards are removed, Insert the cards one by one and
check the voltage. The voltage will fall or reduce when the defective card is inserted.
• Using a soft brush clean the interiors of the case, slots etc., before putting the cover back.

Trouble shooting of the Power supply unit

Some of the symptoms of the power supply failure in a PC are as follows:

  1. The PC sometimes halts during booting and after several tries boots successfully. 
  2. Error codes or beep occur during booting but they come and go. 
  3. The computer hangs or stops for no reason. Sometimes it might even reboot itself. 
  4. Memory errors appear intermittently. 
  5. Data is written incorrectly to the hard disk. 
  6. The keyboard stops working at odd times. 
  7. The motherboard fails or is damaged. 
  8. The power supply overheats and will become too hot to touch. 

Some remedial measures that can be carried out are as follows:

  1. An overheated system can cause intermittent problems. Use compressed air or an antistatic vacuum to remove dust from the power supply and the vents over the entire computer. Check the power supply fan and the fan over the CPU both work.
  2. If a system is upgraded with additional drives and accessories, the power supply unit may be operating above its rated capacity thus causing reboots and intermittent otherwise unexplained errors. Upgrade the power supply unit to withstand the additional loads. 
  3.  An electrical conditioner (Protective device like Surge suppressor) might solve the problem of intermittent errors caused by noise in the power line connected to the PC. 

If all the above checks fail to correct the problem, then check the voltage at the pins of the power supply connectors referring to the pin configuration given below:

Pin configuration for ATX case

Troubleshooting the power supply fan An improperly working fan causes power supply problems. Usually before a fan stops working, it hums or whines, especially when the PC is first turned on. If this has just happened , replace the fan or replace the power supply itself.

If the fan still does not work even after replacing the power supply then it is not the problem with the fan. A short somewhere else in the system and drawing too much power may be causing the problem.
Do not operate the PC if the fan does not work. Computers without cooling fan can quickly overheat and damage the chips. To troubleshoot a non functional fan, which might be a symptom of another problem and not a problem of the fan itself, follow the steps:

  1. Turn off the power and remove all power cord connections to all components, including the connections to the motherboard and all the power cords to the drives. Turn the power back on. If the fan works, the problem is with one of the systems that was disconnected, not with the power supply or its fan. 
  2. Turn off the power and reconnect the power cords to the drives. If the fan comes on, you can eliminate the drives as the problem. If the fan does not come on, then try one drive at a time till the drive with a short is identified. 
  3. If the drives are not the problem, suspect the motherboard subsystem. With the power off, reconnect all power cords to the drives. 
  4. Turn off the power and remove the power to the motherboard by disconnecting P8 and P9 or P1. Turn back the power on. 
  5. If the fan works, the problem is probably not the power supply but a short in one of the components powered by the power cords to the motherboard. The power to the motherboard also powers interface cards. 
  6. Remove all interface cards and reconnect plugs to the motherboard.
  7. If the fan still works, the problem is one of the interface cards. If the fan does not work, the problem is the motherboard or something still connected to it. 

Power problems with the motherboard.

The motherboard, like all other components inside the computer case, should be grounded to the chassis. Look for a metal screw that grounds the board to the computer case. However, a short might be the problem with the electrical system if some component on the board makes an improper contact with the chassis. This short can seriously damage the motherboard. Check for missing standoff (small plastic spacers that hold the motherboard a short distance away from the chassis), the problem that most often causes these improper connections.

Shorts in the circuits on the motherboard might also cause problems. Look for damage on the bottom of the motherboard. These circuits are coated with plastic, and quite often damage is difficult to spot.
Frayed wires on cable connections can also cause shorts. Disconnect hard drive cables connected directly to the motherboard. Power up P8 and P9 or P1 connected but all cables disconnected from the motherboard. If the fan works, the problem is with one of the systems you disconnected.

Overheating Issues

If your computer hangs after it has been running for a while, you may have an overheating problem. First, check whether there is air flow within the case. Open the case and make sure

the CPU and the power supply fans are turning and that cables will not fall into the fans and prevent them from turning when you close the case. While you have the case open, use an antistatic vacuum designed to be used around electronic equipment or a can of compressed air. To blow dust off the motherboard and the CPU heat sink. Check the vents of the case, and clear any foreign material that may be blocking airflow.

After you close the case, leave your system off for a few hours. When you power up the computer again, let it run for 10 minutes, go in CMOS setup, check the temperature reading, and reboot. Next let your system run until it shuts down. Power it up again and check the temperature in set up again. A significant difference in this reading and the first one you took after running the computer for 10 minutes indicates an overheating problem. Try adding an extra case fan or more powerful fans than those you already have. When adding extra fans, for every fan that blows air out of the case, use one that blows air into the case. Also, you can monitor the temperature inside the case using a temperature sensor that sounds an alarm when a high temperature is reached or uses software to alert you of a problem.

Be careful when trying to solve an overheating problem. Excessive heat itself may damage the CPU and the motherboard, and the hard reboots necessary when your system hangs may damage the hard drive. If you suspect damaged components, try substituting comparable components that you know are good.


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