mic repair puzzler

[Jackie Anderson]

I have a Shure 545SD (an earlier version of the SM57, with a switch) that is not putting out: speaking into the business end produces no sound. However, the body of the mic is "microphonic" as heck: tapping on it produces considerable audio output, at least through a mixer into headphones. I suspected the switch (which is a magnetic reed that shorts the capsule), so I took it out of the circuit, but that makes no difference. The connector is wired properly for low impedance, and I am going into a low impedance mixer input. Can anyone offer me any clues?

[Andy Zynda]

Inside the mike barrel, is a small impedance matching transformer. I suspect that one of the wires broke loose, or one of the windings has opened up.
That's assuming that you inspected the dirphragm, and found that it still moved and wasn't obstructed by something.
-andy-