70 volt transformer failure

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Newbie alert!

I have been searching many places for info on this topic, none found. This board looked like a good place to find an answer, so here goes:

Setup - 100 amp powered mixer feeding into a 70-volt audio transformer, powering four (distant) speakers, each with a 70v>4ohm transformer. Taps are set to 10 watts, 4ohm. It has been working fine for two years.

Problem - Entire sytem suddenly has almost no volume. Mic gains used to be at '4', now must be cranked to hear anything. Traced it down to a bad speaker transformer; when taken out of the system, everything returned to normal.

Question- What caused this? The output from the step-up transformer splits to two lines, with two speakers on each. The one that quite was at the end of one of the lines, so it seems any line problems would have taken out the first transformer, not the second.

Monkeywrench - The day before this happened, someone was "messing around" with the systems two tape decks. After the problem occurred, a check of the wiring revealed that some wires were switched: originally, the mono output from the amp (tape out) was divided into the left and right inputs on the tape deck (line in). What I found was that the wires now went into one input (line in) and one output (line out) on the tape deck.


After taking the transformer out (and the speaker, for now), the entire system works fine, gains back down to '4' with ample volume in the remaining speakers. Seems nothing else was damaged.

Finally - Did this cause the transformer to fail, or was it just odd timing? Anyone have any experience with anything like this, or know what would happen when the wires were switched as described?