How to fix/repair your doorbells and chimes
Signaling systems such as doorbells and chimes consist of a push-button switch, a signal unit, wiring, and a transformer to reduce the house voltage-usually to 12 to 16 volts. Before testing a system that won't work, check the circuit breaker or fuse.
Normally, because of the low voltage involved, you needn't turn off the circuit power while working on a signaling system. But on the chance that the transformer is faulty, sending a full 120 volts through the system, check the voltage at the push button. Unscrew the plate surrounding the push button or pry open the button housing. Touch the probes of a neon test lamp to the button's terminals. If the lamp lights, the transformer is faulty; replace it.
Troubleshooting the push button If the neon test lamp doesn't light, test the push button by placing the blade of an insulated-handle screwdriver across its two terminals. If the bell or chime rings, the button unit is corroded or defective. Disconnect its wires and use fine sandpaper to remove any corrosion from the contact points and the wires. Reconnect the wires and retest the button. If it works, reinstall it; if not, replace it. Checking the wiring If the bell or chime didn't sound when you first tested the button, look for loose connections at the button, signal unit, or transformer. The transformer is usually mounted on the side of a metal junction box in the basement or in a hall closet.
Disconnect the bell wiring from the transformer and the push button. Twist together the ends of the wires at the button and test the ends of the wires at the transformer with a continuity tester. If the tester doesn't light, check for broken wires. If you find any, twist the bared wire ends together and wrap them with electric tape or twist them into a wire connector.
The transformer and signal unit
If the wiring is intact, the transformer may be bad. With the power still on, test the transformer's outside terminals with a 12-volt test lamp (available at auto parts stores). If the lamp doesn't light, replace the transformer.
Caution: The transformer is connected directly to the house power. Turn off the power to the circuit before working on it.
Bolt the new transformer to the outside of the junction box. Using wire connectors, join the wires (black to black, white to white) inside the box.
If the bell still won't ring, replace the signal unit with one of the same type and rating. Install it according to the manufacturer's instructions.