TechBlr Tip: How to test cable WITHOUT a cable tester, but with a Multimeter
OK! So you are on a gig or in rehearsal, and the typical happens: You got a bad cable somewhere. Be it an instrument cable or an XLR, there just isn’t anything doing with it.
But, you look in the mic cabinet and all around the booth, but you can’t find the fucking cable tester!!!!!!
Don’t worry, because you don’t NEED it! All you need is a garden variety multimeter!
Ok, so you are probably asking “How do I use this alien technology?!?!”. Probably because you have seen them around the venue, but some of you may never of actually *used* one. With it’s cryptic symbols and strange numbers and threats of requiring some level of math, it was probably something you strove to avoid. But, don’t worry! These meters are actually quite easy to use once you get your head around how to use it (just like any other part of show equipment). And, once you figure it out, you will seem like some technological wizard by knowing WHY something is broken and knowing just what is needed to fix things.
Today, we’re going to be using it for a pretty simple task: Checking to see if an XLR cable is bad. Now this can work with ANY cable, be it a ¼" TRS, XLR or RCA cable. And, in order to do this, we will be checking the resistance of the cable.
To do this, you will need to take your meter and turn the large knob to the resistance setting (With the “Omega” symbol, otherwise known as Ω). Select the 200 Ohms rating and then turn your meter on. If your meter is what is called “Auto Ranging”, that means that it should be calibrated automatically and ready to go. If it is manual ranging, bust out the instruction manual for your meter and find out how to calibrate it before testing anything.
Then, you will hook up the two probes that come with the meter (if they aren’t already attached). One will be a negative lead (usually black) and the other will be a positive lead (usually red). In order to see if a cable is actually working, take one lead and touch it to a pin on the XLR (or a ring on a TRS), and take the other lead and touch it to the other end’s corresponding pin. 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. If all goes well, the meter will range out to zero or near-zero ( 0 ).
If you don’t get any reading, that means somewhere along the line, you got a busted wire. Make sure to test ALL pins (or rings) on the cable to ensure that it works, or that you know which part is the problem.
While a cable tester may be “faster”, a multimeter can do HUNDREDS of things that a cable tester cannot, and can be even cheaper than a cable tester depending on what model you get. And, you can use it to test for everything from bad capacitors to seeing which wall outlets are good to even testing any kind of battery out there! All with the same device.
Multimeters are the live sound technician’s multitool… almost more important than any Gerber or Leatherman. And, even if it is a cheap Chinese Ebay meter, it will serve you well and should always be the FIRST thing you grab before going to a show!
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