Test the Wires
Once cover is removed, look for two, three, or more terminals and wires, depending on how many tones ring in your doorbell system. A standard bell or buzzer has two wires. Detach wires by loosening terminal screws, then connect them to 12-volt circuit tester, or attach them to terminal screws on substitute bell or chime. An inexpensive bell or buzzer or a 12-volt car lamp bulb in a socket with two wires can be used for testing purposes. If test bell or buzzer sounds or bulb lights when you push doorbell button, you will have to install new bell or chime.