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How Do You Test a Transformer?


Testing a transformer should not be performed by someone who is not skilled in electrical testing. You must test the transformer while the hot tub is operational so there will be 115-230v present.

To test a transformer you need a Digital Voltmeter set to 300vac. Transformers take incoming power to the transformer (primary) and reduce the voltage to level the board can use (secondary). On most spas the secondary is 10-15vac. Sometimes there is a second secondary that will be 8-15vac.



As pictured the probes are checking the primary (black and white) or incoming power to the transformer. It should either be 115v or 230v. You must check this with main power ON so extra care is required. You slide the voltmeters probes down the wires into the connector and bearly touch the metal tip of the connector. You should have voltage. If not, you know there is an issue somewhere between there and the incoming power. Most common its the incoming power so check the voltage coming into the spa.

If the power to the transformer passes, move the probes to the yellow+yellow in this picture. That is the Secondary or output from the transformer. It should be 8-15vac. If yes, the transformer is fine. If not, replace the transformer.