Of all the components on a circuit board the transformer gets blamed for a number of issuesthat have absolutely nothing to do with this component. The reasons vary but the fact of the matteris the transformer is the hardiest of all the electronics on the circuit board. Transformers are theoldest of all the components on the circuit board. They predate all the other electronics on thecircuit board. Transformers have been is use in electronics dating back to the time of vacuumtubes.

Transformers have only one job that it has been doing since its inception. That job is to stepdown AC voltage from high voltage to low voltage. All of the electronics on the circuit board runon a voltage that is about 1/10th the voltage of the incoming voltage. An example of this is theinput to a typical transformer is 120 volts AC. The output of the transformer is typically 12 voltsAC. That voltage is then converted to a DC voltage to power the relays. It is then regulated to 5volts DC to power the integrated circuits on the circuit board.

Transformers rarely fail by themselves. The most common true failure is transformeroverheat. This is not a failure of the transformer but a symptom of a failure down stream from thetransformer. A perfect example of this is if a voltage regulator fails and is shorting the input toground, this overheats the transformer and the transformer fails. Another common failure mode ofa board mounted transformer is an open transformer. This is not a failure of the transformer but afailure of the mounting pins due to improper design of the transformer for the application.

Transformers have been routinely blamed for causing a GFCI to trip. This is almostnever the case. (If your GFCI is tripping, check to be sure that it was installed correctly. Licensed

failure to happen, a winding of the transformer would have to physically move on the bobbin andcome in contact with the laminations on the transformer with enough force to abrade the tapecovering the wires and then displace the varnish coating and the nylon coating on the wires. Thenthe laminations would have to be grounded to the circuit board and the board in turn connected tothe ground path. Transformers are specifically designed not to fail in this mode and routinelytested with well over 1000 volts from the windings to the laminations.

A very common reason to remove a circuit board for repair is the technician on site hasused his beeping meter and has tested from L1 to neutral or case ground and has gotten a readingthat he interpits to be a short to ground. This “short” is then blamed on the transformer. When inreality the technician is measuring across the primary side of the transformer which is connecteddirectly to L1 and neutral thru a low amp fuse. The resistance of the primary of a typicaltransformer is 20 to 40 ohms. This low ohm reading will cause the beeping meter to beep. In factthis is a very good test to make when troubleshooting a dead circuit board. The technician, usingand ohmmeter tests from L1 to either neutral or L2 depending on the input voltage to thetransformer and looks for a low ohm reading. This test will confirm that the transformer is notopen and that the connections are good and that the inline fuse is not blown.

As you can see transformers are simple, hardy devices and rarely fail. If you suspect atransformer just perform the above test and then power up the circuit board and test the output ofthe transformer. It should be almost the same as the coil voltages on the relays mounted on thecircuit board. Usually around 15 to 24 volts

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Electricians frequently install them wrong, click here to confirm proper GFCI hook-up). For this

Defending The TransformerTroubleshooting a Balboa transformer