This week's offering is about doorbell systems; how they work and how to repair them.

Four components make up the system:

1) the pushbutton
2) the bell buzzer or chime unit
3) the transformer
4) the wiring

Even if your doorbell works, it may well be loose a common problem with doorbell buttons. Because pushbutton units usually are mounted with small fasteners, the whole assembly often comes loose from the wall. Don't be afraid to use larger fasteners screws or lag screws to reaffix it.

Because it is exposed to weather, the pushbutton unit is the part of the system that most frequently fails. Weather can corrode wire connections in the pushbutton unit causing a system failure. The fix is easy and takes only a little of your time.

There are two types of pushbutton units and therefore two ways to gain access to the wiring. Some pushbutton units have pop-off covers that can be removed with the flick of a screwdriver. The pop-off cover type is easy to recognize because there is no screw or nail head in the cover. The other type is screw-mounted. Remove the screws so that the pushbutton unit can be detached from the wall, exposing the wire connections in back.

Once you have access to the connections, unscrew the terminals and remove the wires from them. Use a knife, a piece of emery cloth or sandpaper to scrape or sand the wire until it shines. Touch the cleaned wires together. The chime should sound. If it doesn't, the problem is one of the other components: the chime unit, the transformer or the wire. Replace the wires on the pushbutton terminals and remount the unit.

The problem of corrosion can also exist with the chime unit. Remove the wires at the chime-unit terminals and clean them in the same fashion as described for the pushbutton unit.

If you have a voltage tester, it can be placed on the chime terminals while the pushbutton is pressed. If no voltage is indicated, it probably means that the transformer unit needs to be replaced.

Voltage testers can be expensive. However you can make one from $2 worth of parts that can be purchased from your local junk yard. All you need is a tail light bulb, its socket and the two wires (about 10 inches in length) that protrude from the socket.

Since a doorbell system is low voltage (usually about 10 to 18 volts), the 12-volt auto-bulb unit can be used as a current tester. Each of the wires is connected to one of the chime terminals. When the doorbell is pressed, the light will shine brightly if the transformer is sending current to the chime unit.

If the light comes on, it means that there is power in the system and the wiring is O.K. Since you have already cleaned the button, this means that you need a new set of chimes that is if cleaning the terminals didn't work.

Doorbell systems are low voltage and therefore are not terribly dangerous. However, the transformer unit operates on high voltage and can be highly dangerous. Power should be turned off when modifications are being made to the system. Persons who do not understand electricity should not work on low voltage electrical systems while the power is on.

If it is discovered that a wire is broken in the wall, look into the price of a wireless doorbell system. It could be less expensive to get one of these than to make a wire repair.