If a single microphone fails, you should first test cabling between which two points?

If the problem affects all mic bars, check the cabling between the TDM and the codec (the TDM is located in the first and, if applicable, second row cable management panels). If the problem is with a single mic bar, check the cabling between the mic bar and the TDM.
Reference: http://www.cisco.com/c/en/us/td/docs/telepresence/ix5000/first_time_setup/ix5000_first_time_setup.html