How to Test a Transformer Before Using It on a TV

Set a multimeter to measure ohms. The first set of tests makes sure that none of the windings in the transformer are shorted to the metallic case of the transformer. Put one multimeter probe to a metal part of the transformer, and touch each wire coming out of the transformer to the other multimeter probe. If the transformer is good, each reading will be infinite. If any of these readings is zero, the transformer is dangerous.

Test each side of the transformer. A transformer is basically two coils of wire, each of which might have taps to somewhere in the middle of the coil. These two coils should be easy to identify. Each pair --- with possibly an extra wire or two --- should come out of one side of the transformer. Measure across any pair of wires from one side. You should see a non zero resistance. If it is zero, the transformer is dangerous. Test all the pairs on both sides of the transformer.

Check for shorts across the transformer. Take a reading from each wire on one side to all of the wires on the other side. All the readings should be infinite. If there is any reading that is zero, the transformer is dangerous and should not be used.