Troubleshooting AV Systems

It's half-way through sound check. So far everything is running along fine, but then it happens. You get to the acoustic guitar played by the worship leader and...nothing. She fiddles with her settings, taps the tuner and...nothing. You check your settings on the board, all appears to be OK and...nothing. This may never happen to you (wink, wink), but it's happened to me.

Some days, it seems all I do is solve problems. Perhaps it's just part of my chosen profession, my strengths makeup, my inability to say "No," or just something I'm really good at. Either way, I do a lot of troubleshooting. It's even to the point of regular troubleshooting sessions via phone or e-mail with friends in different parts of the country. Not that I mind, really. I enjoy the mental exercise of tracking down what is wrong, and the satisfaction—however brief—that another problem is at bay. With that in mind, I thought I would jot down a few notes about what I've learned in 20+ years of troubleshooting AV systems. For this article anyway, I'll focus on signal path issues, as those tend to be the most common in churches. While I'll use examples from the world of sound, the principles are equally applicable to video and data signal lines.

Stay Organized

One of my first rules about troubleshooting has nothing to do with troubleshooting at all. Staying organized will help you troubleshoot should the need arise. If during a soundcheck a mic isn't working, and you have a huge pile of cable on the stage and don't remember what's plugged in where, finding the problem will take an inordinate amount of time. If you set everything up in a clear, organized, logical manner, finding the offending part will happen much sooner. I could tell you how to do all that, but that's another post.

What Changed?

My first question is always the same, "What changed?" If something worked yesterday and now it doesn't, what changed? If it's a wireless mic, the obvious first answer is a battery. A sound or video system could have been re-patched. If you can answer the question, revert back to the pre-change state and see if it works. If it does, you need to determine what negative effect the change has. If not, you have other issues.

Go Linear

Random access is great for video editing and brainstorming, but not so great for troubleshooting. The best approach is to start at one end of the signal chain (I like to follow the direction of signal flow) and work your way to the end. True, sometimes by randomly changing out a cable or a DI you might get the result quicker than I would with a linear approach, but the truth is it's a lucky guess. And you can waste a lot of time (often other people's time if you have a stage full of musicians, and a house full of tech staff waiting on you) running around trying things that might work.

Eliminate the Bad Component

By starting at one end of the chain, the goal is to find a point where it works again. Once you've found that point, back up one component and you've got your culprit. This concept should become more clear in the examples to follow.

Tools and Tips

When starting the troubleshooting process, especially if time is of the essence, take everything you may need to fix the problem with you the first time. Acoustic guitar not working? Better grab a 1/4" cable, a DI, a mic cable and a mic. Why the mic? To test the line. You could also use a signal injector if you have one. As I said earlier, I like to find something that works, then back up a step. Again, the examples should make it clear.

It's most efficient to start at the source of the signal and work your way to the destination. I say this because it's my experience that most often, the sources are the problem. It's pretty rare (in fact, I can't recall it ever happening) that an amp goes bad. So, starting with swapping out an amp is not an efficient step. And if an amp really has gone bad, you'll get to it before long.

No Acoustic Guitar

This problem happened to us this past Sunday. During soundcheck, the worship leader started strumming and… nothing. Not a slight tickle of the meter. First, let me give you an overview of the signal chain. Acoustic guitar —> 1/4" instrument cable —> tuner —> 1/4" instrument cable —> DI—> subsnake —> subsnake —> house patchboard—>patchbay—>M7 (I didn't say it was a simple chain, or even a good one, but it's what we have for now...). So here's how we troubleshoot. First, make sure the battery is good in the guitar (I'm amazed at how often this is the trouble). Next, we check the tuner to see if it's getting a signal. It is. Make sure the guitar is plugged into the input of the tuner, not the output. I've seen this on more than one occasion. Move on to the next part.

Now, at this point we have two options. We could grab a cable checker and check the instrument cable. Or we could just swap it out (because we brought one with us before we started, right?). This turned out to be the problem, but let's assume it wasn't. DI's rarely just fail, but it's good to check to see if it's an active DI that needs phantom power, and be sure phantom is turned on. If that hasn't fixed it yet, we have issues with our lines. Here's how we check those.

First, unplug the DI and plug in a mic. Do you have signal? If so, you've got a bad DI or you need phantom. No signal, try swapping out the cable between the mic and the first subsnake. Still nothing? Go to the second subsnake and be sure you're patched properly. It that looks good, unplug snake 1 and plug in your mic (you could have a bad line in your subsnake). Nothing yet? Head back to the patch panel and check that patch. Then plug the mic into the patch panel. If you don't have signal yet, you have a house wiring problem, or the back of your board is re-patched. At this point, I would quickly verify that channel 15 is actually plugged into channel 15 on the board. If it's still not working, pick another channel and get back to work.

Hopefully that example illustrates the process. The goal is to find some point that works. We could have changed it up a little and made the first step unplugging the DI and plugging in a mic. That would have told us that the problem is between the guitar and the DI. Noting the signal at the tuner, we would now have as suspects an instrument cable (a common point of failure) and a DI (not so much). Swap the cable and 90% of the time you're back in business.

In any case, the point is to make the process as efficient and logical as possible. If you're new to troubleshooting systems, work your way all the way through each time. As you grow in your knowledge base, you can begin to test common points of failure first.

No Sound in the Speakers

I got a call from my former church last weekend as well. They had been hit by a storm which knocked out power, then surged back on. Everything seemed to come back up, but there was no sound coming out of the speakers. They had checked everything they could think of, but still no sound. Thankfully, I wired the system, so I knew the signal chain. Here's what I talked them through.

First, I made sure there was actually signal going to the main mix busses of the board. The meters were working and headphones verified signal at the main mix buss. OK, so everything upstream of the board is functioning. That leaves the DriveRack (a dbx DriveRack 260 speaker management processor)and the amps. I had the tech move to the amp rack and tell me what he saw. Input meters on the DriveRack lighting up? Sure enough, they were. So far so good, the board is sending signal and the DriveRack is getting it. I asked if the amps were lighting up with input lights. Nope. Hmmm, DriveRack getting signal, not sending, odd. I asked what program it was set to...yup it's the right one. I asked if the output meters on the DriveRack were moving. Nope. OK, are the channel mutes on? Indeed, when the DR came back up from a power loss, it muted all the output channels. I've not checked to see if this is a protection mechanism or a software glitch but either way, it held up the signal. Five clicks later and sound was flowing freely.

Interestingly, we had set up monitors 1&2 to run through an UltraCurve EQ, and when he got to the amp rack, it's display was frozen. A quick power cycle fixed that and it started passing signal as well.

Again, the process is the same. We started at point A, the board, and ended at the last point, the amps. Once we found the component that was not passing signal (the DriveRack) we could turn our attention to fixing it.

So the lesson is this; start at one end and work your way to the other, eliminating components along the way. Work logically, and make sure your setup is clear and logical, and you'll be back in business in no time!

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