A residential doorbell is a simple, low-voltage system made up of a push button at an exterior entrance, a bell or chime, and a transformer. The transformer steps down the standard household electric current, typically 120 volts AC, to a lower voltage of between 10 and 24 volts. When a doorbell fails to work, the two probable reasons are broken wiring or a faulty transformer. The solution to the failed wiring is rarely solved with anything but a new wireless doorbell, but a faulty transformer is an inexpensive repair that takes only a few minutes.
Shut off the electrical power to the doorbell circuit at the home's primary breaker panel or fuse box. Typically, the doorbell will be part of the circuit to either the entry lights or the entry wall outlets.
Disconnect the wiring to the existing doorbell transformer. Begin by disconnecting both of the smaller-gauge wires from the two terminals. If two wires connected to one of the terminal screws, it indicates you have two doorbell locations and those two wires should be taped together with a strip of electrical tape to ensure proper reconnection to the new transformer.
Disconnect the house circuit wires from the existing transformer by removing the wire nuts from the connections. The house circuit may also be connected to screw terminals and are removed by loosening the terminal screws. There will be a black (power) wire, a white (neutral) wire and a copper grounding wire. Older homes may not have a grounding wire.
Remove the transformer mounting screws, using a screwdriver. Transformers are usually mounted to a wood framing member, such as a stud or joist. Retain the screws for reuse with the new transformer.
Mount the new transformer to the wall or joist, using wood screws. Connect the new transformer's wire leads wires to the house circuit wires, using wire nuts. Wire-nut the white wires together and the black wires together. Add a strip of electrical tape to the connections to help secure the wire nuts in place.
Connect a single doorbell wire to each of the transformer terminals, using a screwdriver. If two wires were connected to one terminal on the old transformer, reconnect those same two wires together to either terminal and the remaining single wire to the other terminal.
Restore the electrical power to the doorbell circuit at the breaker panel or fuse box.
The doorbell transformer typically is near the entrance door to your home, in the attic, basement, or on the wall inside the entry closet.
Although a doorbell uses a low-voltage current, the risk of electrical shock is still a hazard and care should be taken to ensure the power to the transformer and doorbell wiring is turned off.