Yeah, that will catch a lot of direct shorts and opens but some problems just don't show up until the device has been thermally cycled and baked in for a few th

Yeah, that will catch a lot of direct shorts and opens but some problems just don't show up until the device has been thermally cycled and baked in for a few thousand hours of usage. It's also possible that there was another problem in the circuit which caused overheating in the transformer.