Given that a transformer as wound can only suffer from two faults :- 1, winding open circuit - test with ohm meter, and 2, windings have a short circuit turn. The problem really is does this transformer suffer from a short circuit turn? A short circuit turn will reduce the inductances of all windings by some dramatic factor, like X 30 and as a side issue reduce the Q of each winding (more or less the same DC resistance, inductance goes down to 3% of what is was). So measure the inductance of any winding where you can figure out its rating and an approximation to the likely working frequency. One test for LOPT transformers was to connect the "cal" square wave from a scope to its primary and put a probe on its secondary. A LOPT with a shorted turn gave one pulse on the output while a good one gives perhaps 50 cycles of a ringing waveform - could work on SMPS transformers?
Frank