How to Test a Doorbell Transformer

The doorbell transformer supplies the power to your doorbell chime. If it’s not working, then your doorbell won’t do its job. Troubleshooting a problem in your doorbell transformer is simple. Even replacement is easy.

Step 1 - Using a Multi-tester

Before you do anything, tighten the low voltage wires on the transformer and try the doorbell. If it doesn’t work, get out your multi-tester. Set it to 50 volts AC. Put one of the probes on each terminal. The proper reading should be within 2 volts of the rating for the transformer.

Step 2 - Checking the Transformer

Turn off the power to the transformer's circuit at the service panel. Remove the transformer cover and take out the black wire. Test for power with a neon tester, then do the same for both the ground and white wires.

Step 3 - Replacing the Transformer

With the wires disconnected, unscrew and remove the transformer from the wall, Screw in the new transformer, then reattach the wires to the correct terminals. Tighten them down fully, using the nuts. Use your multi-tester to check the voltage. Try the doorbell to ensure the chime works properly.