OK, I have to go through all of the possibilities even if some are obvious:
- is the phantom switch on the back of your unit on?
- is the phantom LED on the front of your unit lit?
you say your SM58 works into your interface, you are using an XLR to XLR cable plugged into the XLR input of your interface, but the condensers don't work. Once you have verified that phantom is on:
- it's possible you have a bad cable: if the pin 1 connection is broken dynamics will work but condensers won't. Try a different cable.
If none of those help, get a $15 multimeter from Radio Shack. Set it to DC volts. Plug your XLR cable into your interface. Measure from pin 2 or pin 3 to pin 1. You should get something around 48V. With the leads still in, set it to measure current--DC, in milliamps (mA). It should read hopefully at least 3mA and as much as 7mA. Repeat with the other pin (2 or 3) to pin 1. If that works, then your interface and cable are OK.
If you don't get any volts/milliamps, put the leads directly into the XLR input of your interface and repeat the test. If the interface doesn't have voltage or current (and phantom is really on!), then you have a broken unit.
If the direct interface test worked, but the cable into interface didn't, test the cable. Set the meter for continuity or resistance. Measure continuity/resistance between the cable ends: pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3. If all have continuity (or measure less than 1 ohm), measure between different pins (1 to 2, 1 to 3). None of those should have continuity (very high resistance, higher than your $15 meter can measure). If something is wrong here, you have a broken cable.
That should verify that you have working cables and phantom. If you still haven't solved your problem, check one more time that phantom is actually on. Next, try the mics with someone else's interface or phantom-powered preamp, just to eliminate the slim possibility that both mics are broken.
