One approach to testing flyback transformers seems to be to use a circuit
that causes them to ring and observing whether the ringing is damped by
shorted turns. I've never got around to trying this myself.
I have a VT100 that failed with some smoke coming out of the center of the
transformer coil. I tried the ringing test. Here are my results:
http://www.datormuseum.se/peripherals/terminals/vt100
/Mattis