From manual-
A/B Monitor Selector Button (A/B) – This switch selects the output source sent to the Level knob (14). In the A (out) position, the main line output signal is sent to the headphone outputs. In the B (in) position, the signal assigned to the S/PDIF output is sent to the headphone outputs.

Make sure this is set to A.
For SM58 make sure phantom power is off
Make sure nothing is plugged into the 'Insert' jacks on back
Make sure the 'Pad' button is not enabled

While talking into the mic adjust the 'gain' dial until you see a light come on for the signal input LED right above the gain dial. If you cannot get the LED to light up you may have a bad mic cable or other problem.


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