[ The PC Guide | Troubleshooting and Repair Guide | General Troubleshooting Techniques | General Diagnostic Techniques ]

Use the Process of Elimination

Virtually all problems with PCs involve more than one component or subsystem. The difficulty is usually in figuring out which component is responsible for the problem. Using the process of elimination, however, you can usually narrow the problem down rather quickly by making small logical changes and observing the impact on the problem. Your objective is to isolate the cause of the problem so you can correct it.

The key is to make only one change at a time and then see if the problem goes away; if it does, then whatever you changed is likely responsible for the problem (although it could be fixing the problem indirectly in some cases.) If you make more than one change at a time, you cannot readily discern which change was responsible for fixing the problem.

You will want to first check the most probable sources of the problem, and also the things that are easiest to change. For example, if you are having a problem with your disk drive being recognized, it's a lot easier and cheaper to explore things like double-checking jumpers and connections or replacing the interface cable, than it is to try replacing the drive itself. That is something you'd only do after you had eliminated all the other possibilities (or if the evidence implicated the hard disk directly).

Here's a simple example. Let's suppose one morning your PC will not turn on. You hit the switch and nothing happens. There could be many different possible causes for this problem: the power to the house could be out; there could be a malfunction in the wall socket; the surge suppressor that the system is plugged into might have blown; the electrical cord may be loose; the power supply could be damaged. To figure out what is going on you need to eliminate these variables by making small changes and seeing what happens. For example:

• Change the wall socket you are using. If the PC now boots, you have isolated the cause to the electrical wiring in the house.
• If the problem persists, examine the surge suppressor. Change it, or temporarily bypass it and plug the PC into the wall directly. If it now works, the surge suppressor is the problem.
• If the problem still isn't fixed, try changing the power cord.
• If the problem persists still, you may then have to open up the box and look at the power supply unit to see if it might need replacing.

Realize that the key here is making these changes one at a time. If you approach this problem by changing the wall socket you use, bypassing the surge suppressor, and changing the power cord all at once, your problem may go away but how will you know what caused it? This is a valid way to troubleshoot if you have to get the system back up immediately, however. You can then undo the changes one at a time later on to find out what the cause is, in effect doing the same single-change-at-a-time process, but in reverse.

Most problems with the PC can be diagnosed using this sort of process; it's very powerful. You will notice many sequences like the one above in The Troubleshooting Expert.

Next: Do One Upgrade or Assembly Step At a Time

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