Doorbells are a of type home signaling system located near external doors. Other types include door chimes, intercoms and buzzers. When a button on the outside is pushed, a doorbell on the house’s inside emits a ringing sound to signal to people inside the building there is a visitor. Sometimes there are problems, and it is time to do some doorbell repair.
A typical electric doorbell system consists of a button, placed near to the doorknob, a sounding device such as a chime, bell, or buzzer, and a step down transformer, usually placed in the basement or on an attic joist. Pressing the button, which is actually a single-pole, single-throw (SPST) switch, temporarily closes the systems’s circuit, which lets an electrical current flow to the sounding device and activate it until the button is released. There are also wireless doorbell systems which do not require circuit wiring.
The doorbell transformer steps down the household electrical power from 120–240-volt AC to between 12-24 volts for doorbells and to around 16 volts for door chimes. These are not dangerously high voltages, however, before doing any repair work on a doorbell, the power should be switched off at the circuit breaker panel; this is because if the transformer is faulty and not stepping down voltage properly, then you could be exposed to live 120 – 240 voltage, which is definitely unsafe.
Another precaution- never handle any kind of live voltage if you are outfitted with a pacemaker device, no matter how low the voltage.
No Doorbell Sound
There are a few things that can be wrong if the doorbell does not produce any sound at all when the button is pushed.
The first thing to check is if the circuit is receiving power; check for a tripped circuit breaker or blown fuse, and replace or reset if and as required.
The wires in the circuit may be loose at connection points. Tighten any loose wire connections behind the push button plate, in the bell/chime, or at the transformer.
Also, check the wiring for damaged or broken wires, looking for signs of wear or breaks. If required, make repairs by turning off power to the circuit and splicing wires together using wire connectors.
Rusted, corroded wiring terminals could be at fault. Unscrew the doorbell button plate from the wall and look at the backside, checking for corrosion. You can clean any corrosion away by spraying the terminal with a can of electrical contact cleaner, or by unscrewing the wires and sanding the terminals clean with fine grit sandpaper.
Broken sounding device should be checked for next. For this you’ll need a volt-ohm meter (VOM). Unscrew the transformer lead from the terminal on the bell or chime and remove it. Set your VOM on RX100 and test all the push button and transformer terminals. If any of them read infinity or zero ohms, this indicates a faulty sounding device which needs to be replaced or repaired. If this is not the case, then proceed to test the step down transformer, using the VOM.
Turn on power to the circuit. Set the VOM on 50 volt range of ACV. Carefully connect the test probes to the terminal screws on the transformer that hold the signal system wires, wearing heavy gloves. The reading should be between 6 to 24 volts, a reading outside of that range indicates a faulty transformer, which should be replaced. (Make sure power to the circuit is turned off when replacing the transformer.)
Abnormal Doorbell Sound
If the doorbell sounds weak or muffled, the sounding device may need cleaning. There could be dirt or debris between the ringer arm and the bell. Use a cotton swab dipped in a little rubbing alcohol to clean away debris, dust and debris. You can also clean the bell or chimes with a blast of pressurized air from a contact cleaner can.
On a bell, the mechanical arms that strike the bell will sometimes become bent back such that the arm is not striking forcefully enough. If this is the case, try gently bending the arm using a pair of pliers, or replace the unit.
Doorbell circuits sometimes develop a short circuit and ring continuously without the button being pressed. This is usually caused by a faulty push button. You can try to repair this by unscrewing the button plate and inspecting it for pinched together wires or contacts. Separate any wires or contacts touching and make sure all screws are well tightened. You could also just try replacing the button plate entirely if it looks old and corroded.
Photo by sciondriver, Creative Commons Attribution License