How do I know if my doorbell transformer is bad?
To pinpoint the problem, simply test each component with a multimeter, sold at home centers for under $15. There's no need to shut off the power as you troubleshoot because the transformer steps down regular 120-volt household voltage to a safe 16 volts or so.
Doorbell wiring is seldom the cause of this problem, but when it is, I recommend going with a wireless system and skipping the hassle of rewiring. That simplifies the installation process in old houses like yours. You'll just have to occasionally replace the batteries.
6 Easy Steps to Fix Your Doorbell
Step 1: Check the Button
Remove the screws holding the button to the door casing. Unscrew the wires from the button and cross them. If the chime rings, then you've found the problem. Go to Step 3 and replace the button. If the chime doesn't ring, go to Step 2.
Step 2: Test the Button
Set the multimeter to test for continuity. Place its probes on each of the terminal screws in the back of the button, then press the button. If the meter's needle doesn't move, the button is bad and should be replaced (Step 3). If the needle does move, reattach the wires, reinstall the button, and go to Step 4.
Step 3: Replace the Button, If Needed
Attach the wires to the terminal screws in the back of the new button and fasten it to the door casing.
Step 4: Test the Doorbell Transformer
You'll find most doorbell transformers near the main electrical panel. Set the multimeter to voltage setting, and place its probes on the screws where the small-gauge doorbell wires are attached.
If the multimeter reads 16 volts or so, the transformer is fine; go to Step 5. If it's producing less than 16 volts, call an electrician to replace the transformer; this involves working with 120-volt wires and following the electrical code.
Step 5: Test the Chime
Remove the chime's cover. Leave the multimeter on the voltage setting and touch the probes to the wires. Have a helper push the button. If the multimeter shows that current is flowing but the chime doesn't ring, replace it (Step 6).
But if there's no current, the wiring is faulty. If you can find the break, make a splice with 18-gauge wire. If you can't, either pull through new wires or install a battery-powered wireless unit.
Step 6: Replace the Chime, If Needed
Before disconnecting the old wires, label them with strips of tape: "Front" for front bell, "Back" if there's a back bell, and "T" for transformer. Mount the new chime on the wall, and attach each wire to its appropriately labeled terminal.
If the old wires aren't long enough, splice a short length of 18-gauge wire onto each one. Push the button to make sure the chime's working, then put on its cover.
Tools:
Multi-bit screwdriver
Multimeter
Wire stripper