The parts of a typical doorbell system are the push button, the door bell, chimes or buzzer and the transformer. The transformer allows the doorbell to operate on low voltage (6 to 24 volts.) Wired into the doorbell circuit at a junction box, it steps down the voltage from the regular 120-volt circuit. When your doorbell doesn't ring, or rings constantly, the problem may lie in one of the parts or in the wires that connect them. NOTE: To diagnose most doorbell problems, you'll need to have the power source connected. But if you're going to work on the transformer or the wires in the junction box, be sure to shut off the power to the circuit. Remember that the input side of the transformer is high voltage, 120 volts.