Murphy’s Audio Law #10: “The probability of having sound system failure is inversely proportional to the amount of time remaining until the performance.”
We’ve all experienced it—something in our system not working properly or not working at all, and too often, it happens just before the start of a performance.
Although the first instinct might be to take a “shotgun” approach and start checking plugs, connections, cables, etc., in a random fashion (i.e., “panic”), a tried-and-true troubleshooting method will almost always find the problem with less effort and in a shorter amount of time.
The most basic troubleshooting technique (after “Is it plugged in?”) is the “divide and conquer” method. This involves identifying the good parts of the system as well as figuring out which parts have failed. Not only can these working sections be eliminated as the cause of the problem, but they can also be used to test other parts of the system.
For example, a microphone channel on the console is dead, while others are operating properly. The good news here is that you can use one of the working channels to isolate the problem.
First, unplug an input connector from a working channel on the console and plug it into the dead channel. If the bad channel on the console now works, the problem must exist before the console, back toward the mic. If it’s still dead, the problem has to be after that channel’s input (bad channel, dirty insert jack, wrong assignment, etc.). Either way, about half of the system is eliminated.
Let’s assume the first condition above—the console is OK. The remaining part of the system can be divided in half again by doing same thing at the stage end of the cabling. That is, after switching the cables back to where they were on the console, plug a cable from a known working microphone into the offending channel on the stage box.
If the channel stays dead, the problem has to be in the snake. But if the channel comes to life, the snake is eliminated and the problem must be between the stage box and the mic (the cable and/or the mic itself). In this case, substituting either the mic cable or the mic will identify the problem.
How about if a power amplifier is not responding? Take the input cable from another amp that is working—just be sure it is handling the same frequency range if its a bi-amp or tri-amp situation. In other words, DON’T TAKE A BASS FREQUENCY line and plug it in to the offending amp that’s feeding compression drivers/horns!
If it starts working, put things back and move back toward the console—maybe to the crossover. Try reversing the left and right signals starting at the console and moving toward the amps. When the problem switches from one side to the other, you’ve found the problem point in the line.
Again, the tendency—especially under pressure—is to start substituting cables or wiggling connections in a random manner. Although you might just get lucky and hit on the defective component, it’s very easy to put yourself into an endless circle, trying this and that, without really getting a handle on where the problem lies. This is especially true if a section has more than one defective component.
Practice an organized troubleshooting method and you’ll “divide and conquer” your problem every time.
