Troubleshooting

Basic troubleshooting techniques

Preparing a proper work area

You need a clear, flat workspace with an adequate number of main sockets.  In addition to usual work comforts the area should be away from bustle and well-lit.  The following will help:

A compartmentalised tray to keep track of small parts, such as screws and connectors.

Masking tape — to label parts, where they go, and how they are connected.

A small notepad or book to keep track of your assembly / troubleshooting steps.

A magnifying glass to help with reading small part numbers.

Diagnostic and repair tools

Hand Tools

Your tool kit should contain a range of both flat-blade and Phillips-head screwdrivers in both jeweller's-size and medium-size.  You may want to include a small set of miniature nut drivers, a set of Torx drivers, and a special non-conductive screwdriver-like device called an alignment tool.  You also need a couple of pairs of needle-nose pliers and wire-cutters.  When working with older PCs, IC pullers (extractors) may be useful for removing ICs prior to reseating..

Using a Multimeter

Multimeters are available with both analogue and digital read-out and can directly measure values of voltage (V), current in milliamps (mA) or amps (A), and resistance, in ohms (O).  They are referred to as analogue VOMs (volt-ohm-milliammeters), or DMMs (digital multimeters).  You can also use a meter to check diodes, transistors, capacitors, motor windings, relays & coils.

Select the proper measurement function, usually DC voltage for testing the PSU's DC output.  Make the readings between 0V ("ground") and system board power-supply connector.  The DC voltages that normally expected in a PC are +12V, +5V, +3.3V, –5V, and –12V, varying ±5%.

First set the meter to its highest voltage range to ensure that the voltage being measured does not damage the meter.  You can then decrease the range setting to achieve a more accurate reading.

Voltage is measured by placing the meter in parallel with (i.e. wired across) a component, or measured between a pin and ground.  Current is measured by placing the meter in series with (i.e. acting as part of the wire) components.

Resistance is measured in parallel, across a component — but that component must be disconnected from the circuit (leaving, at most, one circuit connection).

The second most popular test is the resistance, or continuity test, often used to test fuses.  The second most popular test is the resistance, or continuity test, often used to test fuses.  Unlike the voltage check, resistance checks are always made with power removed from the system.

Resistance checks also require that you electrically isolate or remove the component being tested from the system.  For some components, this means de-soldering at one end.

If a fuse is good, the meter should read near 0 ohms.  If it is bad, the meter reads infinite.  The resistance function also is useful in checking for cables and connectors.

To check a speaker, just disconnect the speaker from the system and connect a meter lead to each end.  If the speaker is good, the meter should read near 8 ohms.  If the speaker is defective, the resistance reading should be 0 or infinite.

Occasionally you may need to check the mains power being applied to the PSU, usually at the end of the mains lead.  This is rare in the field because there will usually be alternative mains-powered devices you can use to test power leads.  Care must be taken with these potentially lethal voltages.

Information Gathering

Gather information from users about the system's surroundings, any symptoms or error codes, and the situation that existed when failure occurred.  Ask the user to list the steps that led to the malfunction.  This can help you narrow a problem down to a particular section of the computer.

Observe the symptoms of a malfunction to verify the problem for yourself.  Remember: the user is one of the most common sources of PC problems. Look for signs of extended use (frayed cords, missing slot covers) for clues that problems might be caused by usage or aging.

Power-On Self-Test (POST)

Some PCs give number codes on the display, or beep on the internal speaker when errors occur.  Conversely, other PCs display a written description of the error.  The error messages and codes will vary among different BIOS manufacturers and from version to version.  A useful guide can be found at www.bioscentral.com

Initial Troubleshooting Steps

Successful troubleshooting results from careful observation, deductive reasoning, and an organised approach to solving problems.  Begin at the outside of the system and move inward.  Always try the system to see what symptoms you produce and isolate the problem to either software or hardware.  Finally, isolate the problem to a section of hardware or software.

Performing the Visual Inspection

Check the outside of the system first.  Look for loose or disconnected cables.  Consult all the front-panel lights.  If no lights display, check the power outlet, the plugs and power cords, as well as any power switches that may affect the operation of the system.  Try to localise the problem by systematically removing peripherals.

Once inside the case, try swapping suspected devices with known good parts from another computer of the same type.  Try to restart the system after performing each correctional step.

Check all system jumper settings to see that they are set correctly for the actual configuration of the system.  Check the CMOS setup for enabled settings that may not be correct.  Consult any user or operations manuals for built-in self-diagnostic features.  In addition, a manual may contain probable cause and suggested remedies.

Watching the Boot-Up Procedure

1.When power is applied, the power-supply fan activates.

2.The keyboard lights flash as the rest of the system components are being reset.

3.BIOS message displays on the monitor.

4.Memory test flickers on the monitor.

5.The floppy disk drive access light comes on briefly.

6.The hard disk drive access light comes on briefly.

7.The system beeps, indicating that it has completed its POST and initialisation process.

8.The FDD or HDD lights illuminate as the BIOS tries to find the bootstrap loader.

9.For Windows machines, the Starting Windows message appears on-screen.

By knowing the sections involved in each step, you can suspect a particular section of causing the problem if the system does not advance past that step.

Software Diagnostics

The most common packages test the memory, processor, keyboard, display, and the disk drive's speed.  The menu's IRQ Information, I/O Port Information, and Device Drivers options are valuable in locating conflicts.

If a diagnostic program indicates that multiple items should be replaced, replace the units one at a time until the system starts up.

For companies that repair or build computers, diagnostic programs that perform continuous burn-in tests are a valuable tool.  A program runs continuous tests on the system for an extended burn-in period, without intervention from a technician or operator.

Hardware Troubleshooting

After removing the cover, perform a careful visual inspection looking for signs of overheating.  Make a very quick check of the ICs by just touching the tops of the chips with your finger to see whether they are excessively hot. — i.e. hotter than usual.  Check that components and connections have not come loose, and for foreign objects.  Remove any built-up dust.

Field-Replaceable Unit Troubleshooting

Field-replaceable units (FRUs) are the portions of the system that you can conveniently replace in the field.  When exchanging system components, be sure to replace the device being removed with one of exactly the same type.  Just because two components have the same function does not mean that they can be substituted for each other.  Interchanging similar parts is possible in some cases and not in others.

Always check connections after plugging them in.  Look for missed connections, bent pins, and so on.  Try to avoid unnecessary strain on the cable.  Route cables away from ICs as much as possible — some ICs, such as CPUs, can become quite hot and may eventually damage cables.  Avoid routing cables near cooling fans because they produce high levels of EMI.

It is often helpful to just reseat (remove and reinstall) connections and adapter cards in the expansion slots when a problem occurs.  Oxidation may build up on the computer's connection points and cause a poor electrical contact.  By reseating, the contact problem often disappears.

The Shotgun Approach

When you have no idea what the problem is, you should test all external devices before removing the outer cover to check internal devices.

The basic system consists of the system unit, the keyboard, and the display.  Other devices are optional as far as the system's operation is concerned.  When a problem occurs, you should first remove the optional items from the system.  By doing so, you divide the system in half and can determine whether the problem exists in one of the main components or in one of the options.

The next components to exchange are the floppy drives and the power-supply unit, in that order.  The system board is the last logical and most difficult component to exchange.  Therefore, it should be the last component in the system to be exchanged.