If you one day find yourself with a transformer that might or might not have a shorted winding, your first inclination for verifying your suspicions might be to find an inductance meter. The problem with powering up an inductance meter for this situation is that the inductance of a transformer containing a shorted turn might not be much different from that of one that’s fine. Thus a reading on an LC meter might not reveal much about the transformer health.

A better approach is to employ a ring tester. A ring tester for inductors or transformers basically checks the inductor Q. (As a quick review, the electric energy stored in the inductor divided by the energy dissipated during one period.) A shorted turn makes the transformer/inductor more lossy and thus reduces its Q.
The ring tester checks for Q by applying a pulse to the DUT and then counting the number of cycles in the ringing waveform that results. More specifically, it counts the number of decaying cycles containing energy above a predetermined threshold. The number of cycles above the threshold constitutes a measure of the transformer/inductor Q. Transformers/inductors that are functioning properly will have a high Q; those containing shorted turns, not so much.

It is relatively easy to find DIY circuits for ring testers, and ready-to-go units can be found online for about $60.

M181 LCR meter is a practical kit for measuring the R, C, or L of either through-hole or surface-mount components. It features about 1% accuracy, which is adequate in most engineering scenarios. Not only being very easy to build, it also includes a Self Test mode that helps users to verify the correctness of assembly. Compact in size and the capability of serial output make the meter a great choice for many embedded applications.

Highlights of M181 LCR Meter:

Resistance range: 0.1ohm — 10M ohm
Capacitance range: 1pF — 10000uF
Inductance range: 1uH — 20H
Fully automatic ranging
Accuracy: about 1%
Measurement frequency: 1KHz/100Hz selectable