Sometimes electrical appliances stop working without any obvious signs as to why. A lot of people don't know what to do when this happens and they throw something out that can be easily fixed. It's true that a lot of products today are designed to be disposable, but armed with a little knowledge you just may be able to salvage something that would otherwise be consigned to the scrap heap.

This Entry will cover some basic techniques for troubleshooting common problems with small electric and electronic items, hopefully without electrocuting yourself in the process. While the focus will be upon appliances, it must be remembered that in the UK, DIY repairs or any other work on mains electricity should only be done by a registered, qualified electrician. Elsewhere in the world it may be the same, and the wise 'handyperson' should consult a professional before sticking a screwdriver somewhere unfamiliar.

A Word About Safety

Speaking of electrocuting oneself, before we go any further we should have a little talk about safety. Unlike in the days of vacuum tubes¹, most electronic equipment today operates on low voltages: however, the appliances actually use mains electricity that is converted to a 'safe' voltage internally or externally by a wall adapter. Just because the electronics themselves run on five volts does not make the whole device safe.

Always make sure equipment is powered off when you are working on it! There is still the possibility of large current flows which could cause fire or burns, or more likely, you will cause damage to the equipment itself when you drop a screw inside or cause a short circuit as you poke the innards with a metal tool. This means not just turning off the power switch, but unplugging all power cords and removing batteries (if there are any). If the device is solar powered, it is best to work on it at night².

An exception to the statement about high voltages is anything that has a Cathode Ray Tube (CRT), such as televisions and computer monitors. These work with voltages that can easily exceed 20,000 volts, and to make matters worse, the voltage can still be present even when the device is unplugged. Unless you are an expert, you should stay away from opening a TV or computer monitor. Microwaves are in a similar risk category to CRT monitors. Don't even go there.

Still talking high voltage, modern electronic circuitry such as that in computers, radios, and calculators, can be sensitive to the high voltages that are generated by static electricity. Static charges you build up can easily damage the components inside this equipment if you should touch them. A common example would be installing or removing a circuit board in a computer. There are conductive wrist straps and mats that you can buy to protect equipment from static charges, but if you want to avoid the expense, you will generally be safe if you touch the metallic case of the equipment (eg, a computer) before touching any of the internal components.

Some equipment contains more dangerous stuff: lasers, microwave ovens, radio transmitters, etc. Most smoke detectors contain a small piece of radioactive material. You should just stay clear of these and leave them to an expert.

A 'quick' guide to safety could be:

• Small power devices using less than 5 watt are mostly safe (unless high voltage is involved).

• Devices generating heat (even as a by-product) are dangerous.

• Devices with a motor rating over 500 watt are dangerous.

A Note of Warning

While almost everything has the standard 'no user serviceable parts inside' label, there are some items that really aren't designed to be repaired. Some may be permanently sealed shut, or may contain many tiny parts that are virtually impossible to get back together. Some may require special tools like a star- shaped screwdriver to open. If in doubt, chuck it out.

Some appliances have specific discharge resistors fitted to make things safe in a few minutes, some seem to rely on natural leakage, and some even have a nice label inside saying something like 'Unplug and leave to discharge for x minutes before coming near this area'. Just about anything that is mains-powered and electronic is likely to contain big capacitors in the power supply that could give you a nasty belt of electricity if you don't discharge them first, even when unplugged. Not enough to kill you directly, but enough to make you drop whatever you're holding, jump back and hit your head on something etc. The same applies to mains filters and simple mains/battery devices like shavers.

Know Your Limitations

This Entry is mainly about small electronic devices such as radios, small appliances, toys, telephones, etc. Larger items like washing machines and refrigerators have electronics but obviously have a mechanical aspect to them as well. Use common sense in deciding if you are capable of tackling these items. For a small inexpensive item you have little to lose by trying to fix it, but think twice before working on something valuable or difficult to replace. You probably wouldn't take apart a car engine or an antique gold pocket watch just for fun, so think twice about opening up that new DVD player or camcorder just to see what makes it tick.

Debugging Techniques

There are some general rules that apply to diagnosing any repair. Be logical. The device must have broken for a reason. When did it last work? Did something change about the way you use it? Were there any clues when it failed (eg, a funny smell, smoke, a thunderstorm)? Is it completely dead or just malfunctioning in some way? Generally a completely dead device indicates a simpler problem than one that malfunctions in some more subtle way.

Checking the Obvious

Surprisingly often the problem may be something so obvious that it's overlooked. Is it plugged in? Are you sure it is getting power? (plug something else into the same outlet to make sure). If connected with a power bar, is the power bar plugged in, turned on, and known to be working? Can you swap the power cord with one that is known to be good?

One of the first things to check (if the thing is completely dead) is the fuse in the plug, followed by any fuses accessible from the outside of the device. Always replace a fuse with one of exactly the same type and rating.

More complex devices with many switches, like clock radios, may appear to be non-functional because the switch settings were changed.

Many devices have more than one power switch; computers are notorious for this. There may be one power switch on the front but there is likely at least one more on the back that may be turned off. Also check the mains wire is firmly inserted into the socket.

With battery operated items check or replace the batteries. Don't assume that the replacement batteries are good - test them. Make sure the batteries are inserted correctly. Are the batteries loose? Sometimes batteries fail to make contact, and this can be corrected by slightly bending the clips that contact the battery. Make sure the batteries are of the correct type; this is important for items like watches and calculators where there are many similar types. Rotate the batteries in place to clean the contact areas (try this before bending the clips - they may break on trying to bend them). Also check the contacts for corrosion as sometimes a white oxide is present on the surface.

Some items, such as hair dryers, have switches for the line voltage setting. Make sure it was not inadvertently set to the wrong position.

Many devices today use AC adaptors - those little square power cubes that steal all the outlets from your power bar. The AC adaptor could be bad or have been replaced with the wrong one. A good functioning adaptor is slightly warm, not hot or environment temperature. Adaptors come in many different voltages and polarities and are not interchangeable even if the connector appears to fit. If it fails or has been lost you can buy a 'universal' adaptor as a replacement.

Look At All Those Bits!

Once you've eliminated the obvious, it's time to open up the device and look inside. A visual inspection is really all you need to do. Look for loose wires or parts, burned components, or leaky batteries. Look for burned fuses inside the device.

Some devices, such as cordless phones, may contain rechargeable batteries. These have a finite lifetime and eventually need to be replaced. Usually they will slowly fail to hold a charge over a period of time rather than simply failing, but sudden failure is possible. Check with your local authorities for instructions on the disposal of old rechargeable batteries as they can contain toxic chemicals that are harmful to the environment.

Tools of the Trade

Digital multimeters can be bought inexpensively at most hardware or building supply stores. These will let you measure voltages as well as checking continuity of wires and fuses. Use caution when measuring voltages; only try this on battery-operated devices and with voltages not exceeding 42 volts. To fix broken wires, you will need a soldering iron. For electronic devices, use a low wattage soldering pencil type, not a soldering gun as this will overheat and damage sensitive components. Do not use the acid core solder intended for plumbing, the acid will slowly eat away at the wires.

When partially dismantling equipment with lots of wiring, a digital camera can be invaluable. Taking plenty of pictures from different angles before starting to disconnect, and then some more during the process can be very useful when it comes to connecting everything back up again. A great help in being able to reassemble any device is arranging the screws and parts in sequence of removal. A saucer³ or small plate for each layer comes in handy.

Replacement electronic parts can be purchased at stores such as Radio Shack. These can be expensive, however. If you do a lot of repairs you should try to build up a 'junk box' of spare parts kept from devices that couldn't be repaired or have been discarded by other people.

Computers

You are not realistically going to be able to unsolder that Pentium chip from your computer and put another one in. The surface mount technology used in most computer circuitry is manufactured using robotics. You can, however, do some maintenance that may avoid problems before they occur. Computers tend to accumulate a lot of dust inside which can make the fans less efficient at cooling. Opening up your computer and cleaning it out is recommended every few months, depending on how dusty the conditions are.

A vacuum cleaner is not recommended - it is too powerful and can generate static electricity. The experts use cans of compressed air to blow the dust out, unfortunately these cans of air are quite expensive. Being dry and usually not strongly adhering, a little bit of directed exhalation often removes most dust clogging up CPU fans, etc (though breathing in again before getting your face out of the dust cloud can be unpleasant), or you could try a small brush. In a pinch you can just pull the largest of the dust balls out by hand. Make sure the fans are clear of dust and running smoothly. A shot of spray lubricant can do wonders for ageing fans⁴.

The fan mounted on the CPU chip often fails after a couple of years. If you hear strange grinding sounds from inside the computer, the bearings in the fan have likely worn out and are about to fail. You should replace the fan as soon as possible, otherwise the expensive CPU chip will likely fail due to overheating.

Keyboards also tend to collect dirt and dust. If you don't have a can of compressed air to blow it out, you can carefully pry the keys off most keyboards and clean them with cotton buds. Bigger keys such as the space bar and the 'Enter' key should not be removed. These often have additional bits which make them very difficult to put back in place.

Make sure you draw a diagram of the keyboard locations before you remove all the keys so you can easily replace them. As long as it's unplugged (and not attached to a laptop) you can rinse keyboards under the tap. Let it dry thoroughly before plugging it back in.

Telephones

With cordless and mobile phones the most likely problem is with rechargeable batteries. Wired phones, unless it is as simple as a faulty cord, are difficult to repair. Many telephones are now manufactured based on achieving the lowest possible cost and they are essentially disposable.

Note that the voltages used for wired telephones is high enough (48 volts) that it can be considered dangerous, and an even higher alternating current voltage is used for ringing, which is potentially fatal⁵.

Small Appliances

Small appliances such as blow dryers, etc have few electronics and simple broken wires or faulty switches are often the cause. Some devices have internal fuses, possibly soldered in, which can fail if the devices overheat. Make sure there is no obstruction (such as fluff) in the air flow before testing the device.

Audio Equipment

A common problem with older or lower cost audio equipment such as stereos, portable radios, and CD players is that the controls for volume, tone, or other settings become noisy. Often this can be fixed using contact cleaner, or try simply running them quickly from one end to the other a few times can clean the track and/or wiper, and remove most or all of the crackle. Loud speakers often fail because of the wires coming loose from the contacts inside. This can happen when speakers are moved around a lot.

One fixable problem common across a range of manufacturers and models is headphone sockets on personal music players becoming unreliable due to failing connections between the circuit board and PCB-mounted socket. Just sweating the solder with an iron often fixes things, and a little more solder almost always does (for this sort of repair, a set of jeweller's screwdrivers is invaluable).

For cassette players in general, drive belts being displaced or breaking are common faults (you can often hear the motor turning but nothing moves). Replacements can be very cheap, though getting them into place can be extraordinarily fiddly and frustrating.

When All Else Fails

If all else fails and you can't fix it, you have a good excuse for purchasing a shiny new gadget. As one h2g2 Researcher reports:

I have a microwave oven that is almost 20 years old that set me back almost US$1,000 when new and is still working perfectly. I'm getting a little tired of the simulated wood grain finish and am eagerly awaiting the day it fails so I can buy a new one.