If your doorbell suddenly stops working, it could mean the transformer box has malfunctioned. The transformer box is commonly about two inches long with two narrow wires, and it connects to a power source somewhere in your home like a closet, basement or attic. Here are some tips to replace doorbell transformer boxes.
Turn Off Power and Gather Tools
For this repair, you need: a voltage tester, wire stripper, wire nuts, electrical lock nut, screwdriver, needle-nose pliers, and replacement transformer. Before you make electrical repairs, switch off the breaker to turn off the power to the junction box. Though doorbells do not use much voltage, you still run the risk of electrocution. Run a voltage tester over the transformer to ensure there is no current.
Remove the Old Transformer
Take off the junction box cover with the screwdriver, and test for voltage again. If the voltage meter detects a current, turn on the breaker, run the voltage meter over the junction box again, and turn the power off. You should see a black wire and white wire on one side of the junction box.
Undo the wire nuts that secure them to the box, and pull them out. Disconnect the wires on front of the transformer, take them out, and remove the transformer by loosening the lock nut with needle pliers.
Install the New Transformer
Look for markings on the transformer box that tell the location of the wiring. The black wire is usually hot, the white wire is neutral, and a copper or green wire is ground wire. You may prefer to turn the power back on, test with the voltage meter, and turn the power off.
Set the new transformer into the knockout hole, and connect the black wire. Trim the black wire down to ½ inch of bare wire with the wire stripper, secure it with a wire nut, and repeat for the white wire. Attach the ground wire with a screwdriver, or if there isn't a ground wire, cap off that wire.
Connect the doorbell wires to the screws on the front of the transformer. There are usually two screws: one for the chimes and one for the button. A third screw will be for the speakers. Connect the hot wire from the button to the red screw on the transformer, and connect neutral wires to any other screw color.
Turn on the power, and test the doorbell. If the doorbell still doesn't work or you don't trust your skill, contact an electrician like SDS Electric to fix the problem.