Balanced audio cables are cables that carry signal on two wires and are insulated by shielding that acts as a ground. A balanced cable has three connections. The most common types of connectors for balanced cables are XLR and tip-ring-sleeve (TRS) quarter-inch connections. Any of the three connections of a balanced cable can fail, which will result in a poorly functioning or a completely useless cable. In the event that any of your balanced cables fail, it is beneficial to know how to test the cable and locate the problem.
Set your multimeter to measure resistance. Resistance is measured in ohms, which is how your multimeter may be labelled. Audio cables should have little resistance in the wiring. By measuring for resistance, you can verify that your wires are properly connected inside the cable.
Calibrate your multimeter. Touch the red and black probes together. Your multimeter should give a reading of zero ohms. If the reading is anything else, use the calibration control to set the reading to zero while the probes are connected. If you have a digital multimeter, you do not need to calibrate it.
Test your ground. On an XLR balanced cable, the ground is pin one, which is the left pin when the middle pin is pointed upward. On a TRS balanced cable, the ground is the sleeve of the connector. Connect one probe to the appropriate connection point on each side of the cable and check for a zero or near-zero reading on the multimeter.
Test the positive and negative connections. On a XLR balanced cable, the positive and negative connections are pins two and three, respectively. Pin three is the middle pin. On a TRS balance cable, the tip is positive and the ring is negative. Connect the probes to both positive contacts and check the resistance reading. Then connect the probes to the negative contacts and check again for a zero reading.
Plug your cable into your cable tester. Your cable tester should have jacks for both XLR connectors and quarter-inch TRS connectors. Be sure that both ends of the cable are fully plugged in.
Set the tester to the proper cable type if necessary. Some cable testers require you to choose the cable type for an accurate reading.
Check each connection of the cable. Many cable testers have a knob that will select each connector and show a reading for that specific wire in the cable. Both balanced XLR and TRS cables have three connections, so be sure that all three are functioning properly. Most cable testers will light up if the connection is good.
Refer to the tester's manual for more explanation on the tester's readings. Some testers have a light grid that will tell you the status of all of the connections at once. You may have to check the manual to interpret these results.