If you buy a computer through a Web site, by mail, or from a discount store, an office supply place, or some other national retail chain, remember to ask about repairs.

Obviously, it's a lot more convenient to have somebody come to you to perform repairs, but that kind of service is almost always an extra-cost option. Other options include taking the computer to a local carry-in service or sending it back to a factory repair center in another city.

There are a few disadvantages to shipping out your computer. First, if you didn't save the original packing materials, you either have to order (and pay for) an empty shipping box, or run the risk of having the computer damaged inside an improvised container.

Second, most companies expect you to pay for shipping, so repairs from a distant center are usually more expensive than local work. Finally, you can expect to be without your computer for a longer period of time because it may take several extra days for delivery.

Can you do your own repairs?

Fortunately, there are very few computer problems that make it necessary to return the whole system to a repair center. In most cases, the computer maker's technical support center can diagnose a problem by telephone or e-mail and send you one or more individual replacement parts.

If you (or a member of your family or staff) can open the case, remove the old part and install the new one, you can often perform the repair yourself without the need to take the computer to a repair shop or call an on-site service technician.

Of course, you may want to let the authorized service people handle any repairs that may become necessary during the warranty period. But after the warranty has expired, you can save both time and money by handling routine service and upgrades on your own.

If you do expect to do your own work, the type of service offered by the people who sold your computer to you may be less important than the quality of the information you can obtain from their support center.

Caution Don't think about repairing individual circuit boards; it isn't worth the time or effort to troubleshoot parts down to the component level. Most manufacturers simply replace bad motherboards and other printed circuits with new ones. You should do the same.

Also, don't try to repair your own video monitor, especially if it has a CRT display. The capacitors inside a video display can hold a lethal electrical charge, even if the unit is disconnected from AC power.

Remember, laptop computers offer a completely different set of problems. Just because you have successfully done work on one type of laptop is no assurance to expect the same kind of luck with a different make or model.

You probably need specific instructions, just to get to the part you want to replace. Because most laptops use a combination of standard components (hard drives and memory modules) and proprietary parts (just about everything else), it may not be possible to do any repairs unless you obtain parts from the manufacturer.

Finding a service manual

A service manual or some other source of detailed instructions is essential for many repairs. Without some kind of specific instructions for opening the case and removing various interior parts, you can sometimes spend more time trying to get the computer open than it takes to actually perform the repairs.

This is common for most makes of laptop computers, but it can also be a problem for some desktop systems that don't use generic cases.

Fortunately, most of the major computer makers offer free service manuals on their Web sites. Many of the smaller computer builders use cases, motherboards, and other parts that come from third-party manufacturers who also offer free service manuals or other online documentation.

If a service manual was not supplied with your computer, follow these steps to find one online:

• Go to the computer manufacturer's Web site.
• Look for a link to Support or Downloads and jump to that page.
• Find the link to the specific model name or number of your computer.
• At the page devoted to your computer, look for a link to a Service Manual.

The specific route from the home page to the Service Manual is different for every computer maker, but most lead you to a service document of some kind. If you can't find a service manual online, call or e-mail the company that built the computer and ask for the specific instructions you need.

If you can identify the original maker of your computer's motherboard, hard drive, or other modular part inside the computer, you can probably find a manual or other service information from that company's Web site. The name of the original equipment manufacturer (the OEM) usually appears on a label or printed directly on a printed circuit board.

Are parts available?

Most desktop computers are assembled from common modular parts, so it's generally quite easy to find replacement parts for repairs and upgrades. When you need a replacement, you don't have to find an exact match for the original.

As long as it has the right type of connector to fit a socket in the motherboard, it doesn't matter if the new part is the same make and model. For example, if you need a new video controller card, you can go to a computer store or an online retailer and choose any card with the same kind of connection to the motherboard that offers the performance specifications you want, even if it's a different brand from the original.

When you're ready to upgrade the computer with an additional memory module or hard drive, you can choose the one that offers the best combination of price and performance, regardless of who made it.

But some computer parts, especially in laptop systems, are unique to a specific model. The only source for these parts is the original manufacturer. This should not be a problem if you need warranty service, but after a few years, some essential parts might no longer be available.

By the time you have handed down the computer to the second or third child in the family, or relegated it to duty as a backup for low-priority use in your business, it could be extremely difficult to find a replacement for a worn-out switch or a damaged display screen.