I was using my Steinberg UR22-MKII, MXL 990 setup for 4-5 months without any problems. But today, suddenly when the mic was connected (and working), the mic suddenly stopped giving output. I couldn't find the problem. Here are my findings.

  1. There is a ground noise (humming) when holding the microphone in my hand and if I touch another metal object, the humming stops. But mic still doesn't work. I also feel a small electric shock in my finger when I do this.
  2. I also have a dynamic behringer mic, which still works with the same audio interface.
  3. I tried different USB ports (that power the interface), and different computers, same results.
  4. I tried unplugging the computer for possible grounding issues. Same result with battery power.
  5. Touching the audio interface while holding the microphone also erases the ground noise within the interface, which is the noise, independent from the microphone (inherent noise).

I don't have another condenser mic or another audio interface to figure out which one is faulty. Dynamic mic working fine, suggests that the mxl 990 can be broken, but the problem can also be in the phantom power mode of the audio interface, which the dynamic mic doesn't make use of.

I want to find out which one is faulty, so I know which one to replace. I don't want to order a new expensive microphone (yes mxl 990's are also expensive in my country), only to find out that the audio interface was the faulty one.

I am open for any suggestions, thank you for your time.

Edit1: I did the tests, the answer suggested. When the interface is connected to the computer, the 1-2 and 1-3 ports give 47.8V as suggested. But when the cable is connected and the tests are done at the end of the cable, I read 0.02V or 0 V, this means that the cable is faulty. But then how can the dynamic mic work with the same cable ?

Answer: Turns out faulty wire. Somehow one of the cables was disconnected from its base inside the cable adapter. Fixed after soldering.

1 Answer 1


You need a multimeter to measure the voltage and current.

I assume this XLR pin usage:

  • 1 .. ground
  • 2 .. positive
  • 3 .. negative

If XLR pin usage is different in your setup you will need to switch pins with the pins I describe below accordingly.

Measure Interface and Cable

Do the first measurments directly at the interface XLR port and optionally a second measument with the cable plugged in and measure at the end of the cable, obviously you can skip that if you know the cable is not faulty.

Set the voltage range of your multimeter so it can measure 48 Volts DC or more.

  • Measure between pin 1 and 2, note the value. It is probably not 48 Volts but a bit less, like 45 V. That's okay.
  • Measure between pin 1 and 3 and compare the value, it should be the same with 0.1 Volt difference at the most (maybe adjust with measuring tolerance of multimeter). You can ignore the sign of the measured values.
  • Measure between pin 2 and 3. The voltage should be exactly 0.

Now set your multimeter to a current range of up to 20mA or more and measure the current:

  • between pin 2 and 1 it should be 7 mA
  • between pin 3 and 1 it should also be 7 mA

(Measuring on the end of a long cable may reduces the current or voltage.)

Measure Microphone

In order to check a microhpone you need to measure the resistance with the multimeter.

  • Dial the largest measurement range for resistance and measure between pins 1 and 2 and between 1 and 3. Both times you need to see an "open" reading, meaning the value is very high or too high measure. Check the manual what your multimeter displays in such cases. (In my case it shows "1." which can be misleading because it looks like a small number but the lack of decimal places signals that it's actually on open connection.) If you have not an open connection but a low resistance here, then their is something wrong with the microphone.
  • Measure between pin 2 and 3 should give you a short, meaning a quite low resistance.


If you get different or odd results when measuring the XLR port you most likely have a faulty interface. If the cable measurements differ from the interface measures, then the cable is broken. Otherwise the mic is faulty, especially if the resistance measurement doesn't match the expectations.

  • Thank you for your answer, the peak indicator in the interface flashes when doing the current tests. Is that normal ?
    – Rockybilly
    Commented Aug 18, 2020 at 14:11
  • Also, can I make similar tests to the condenser mic using the multimeter ?
    – Rockybilly
    Commented Aug 18, 2020 at 14:45
  • Also 2, please check the edit.
    – Rockybilly
    Commented Aug 18, 2020 at 15:12
  • Yes, it's normal for the peak indicator to flash, because when connecting the probes of the multimeter impulses occur. Also, it's best to have gain knobs on the interface turned fully down. Yes, it seems the cable is borken, this can be caused by some kind of breaking that leads to a short-circuit. It is possible that the cable still carries a signal well enough for dynamic mics because in this case there are very low voltages involved, a shorting only occurs when there's a significant voltage like 48V. I add a parapragh on measuring a mic to my answer.
    – Matt
    Commented Aug 19, 2020 at 6:45

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