From a repair perspective, doorbells are extremely simple devices. You have a power source, the box with the chimes, and one or more switches that are connected to the chime box with low voltage wiring. Unless you are someone who really likes soldering and tinkering with electricity, repairing a doorbell is mostly about finding which part is failing and replacing it.
Always start any electrical repair job with the basics.
Make sure that there is power to the chime box. You may have blown fuse or a thrown breaker. Either of these will keep your doorbell from ringing. Anytime an electrical device fails to come on, always check the power source. If the power seems to be in good working order, it is time to move on to the next possible problem.
Leave the power on while you check the switches.
Because the wiring running to the doorbell switches is low voltage, you do not really have any worries about electrical shock at this point. Remove the screws that fasten the doorbell switch to the house or door frame. Gently pull the switch assembly away from the wall. Because the wires running to the switch are pretty small, be careful because you do not want to break them off inside the wall. You will probably only have about three to six inches of wire to pull on at the switch.
Once the switch is loose, inspect the screws that fasten the wires to the back of the switch.
If one or both of the wires are loose from the screws, this is most likely the problem. Tighten them up to the screws and test the doorbell. If it works, you are finished. This is rarely the problem. If the wires are attached properly and seem to be intact, unscrew them from the switch. When both wires are loose, touch them together. If the switch is bad, the doorbell will ring. At that point, you need to buy a new switch and install it.
If the doorbell still fails to ring, it is time to move on.
Replace the wires and reattach the switch to the wall. If your doorbell has multiple sounds caused by different locations, like the front door and back door, usually only one switch will fail to work. This normally means that half of the doorbell chime has failed. Once a bad switch has been eliminated as the problem, the chime box is the next thing to check.
Turn the power off before starting to remove the chime box.
The chimes inside the doorbell use full current instead of low voltage. You want to cut the power before sticking your hands inside the box. The outer cover generally snaps into place. Check for any screws that may hold it on before trying to force it to pop off of the box. It may have push tabs that release it. If so, depress these and remove the cover. Look inside to make sure that there are no loose or broken wires. If there are, you may be able to just repair or reattach these to fix the chime.
The doorbell will be attached to the wall with a couple of screws.
Remove these screws and lower the box. Look at the back of the box to make sure that the wiring looks okay from that angle, too. Track the wires up to where they are connected with screws or wire connectors to the doorbell. Loosen the wires and remove the chime box. It is time to head to the home center and buy a new door bell chime box.
Buy and appropriate replacement box to install with a chime sound that you like.
The new doorbell may come with new exterior switches. If you like these better than your old switches, you can replace the switches while you have your tools out. However, the old switches should work just fine with the new box. Attach the wires per the manufacturer’s instructions to the new chime box. You may need to put new anchors into the drywall to hold the new box in place. If you are lucky, you will be able to use the old ones, but do not count on it. Once the new box is in place, test it. If it sounds from all switches, you are finished.