It happens to everyone at some time: it was working fine yesterday, an hour ago, or the last time you used it, but it’s not working now. In the good old days most recording engineers were also good technicians who took troubleshooting in stride, but that’s not always the case today. More musicians are coming to recording from a non-technical background, and today’s equipment is complex. Going behind the rack, finding a cold tube, and swapping it out to get the session running again just doesn’t work any more
But all is not lost. Today’s modern studio equipment, even budget gear, is highly reliable. More often than not a problem that crops up unexpectedly isn’t an internal equipment failure, but something external. Common sense often fails us in time of panic, but with a cool head and a logical approach to trouble-shooting you can solve most problems and get back to work promptly.
The first step to solving a problem is to isolate it. In this article we’ll look at common failure points and how to locate them.
What’s the problem?
There are some failures that are obvious, though not necessarily for obvious reasons—like the tape doesn’t move or there’s an incomprehensible error message on your computer or effect processor display. Those have their unique solutions, and they require troubleshooting tools and techniques beyond the scope of this article.
But problems that you can usually solve quickly fall into two broad classes: either something’s dead (or nearly so), or you’re hearing more than you expect—artifacts that aren’t supposed to be there, such as distortion, hum, or extraneous noise.
If a problem occurred after you made a change, that’s a clue but most of the time it’s not that simple. Let’s assume for now that something just quit on its own and get down to business. Most troubleshooting techniques are obvious as you’ll see, but the trick to locating a problem is to diagnose it and eliminate the possible causes in a logical manner.
Is it plugged in? Is the power switch on? Everything used to have an on/off switch and a pilot light, and we were accustomed to turning anything on before using it. But in this cost-conscious age, power switches on equipment that consumes little electricity have gone away along with pilot lights (except on retro gear, bless it) so the presence of primary power isn’t as obvious as it used to be.
Conventional power cords are usually pretty reliable, but wall warts are notorious for falling out of power strips in the back of the rack or a dark corner, and their connectors don’t lock securely into the equipment. Things are always getting moved around, and it’s easy to dislodge a power connector inadvertently (or any connector for that matter).
I own a compressor with neither a pilot light nor power switch, and the only visual indication that it’s on is when it’s getting an above-threshold signal. Once when I couldn’t get a signal through it I didn’t discover that the power plug had fallen out until after spinning my wheels looking for a bad input cable. Maybe I’ll remember next time.
Oops wrong button
Are you trying to do something illogical? Is a channel turned off? Are you trying to record on Track 4, but the signal is assigned to Track 3 because the pan pot is turned the wrong way? Is the recorder switched to Input Monitor when you’re expecting to hear playback? Did you leave something patched into your signal path that’s turned off?
There’s more obvious stuff here, but don’t ignore it. We all make operating mistakes now and then. Just be sure that you actually have a problem before you go looking for it.
Cables and connectors are the most common source of problems. And no wonder—a typical 8-track setup with a modest patchbay might involve nearly 100 cables with 200 connectors, each containing two or three wires with terminations at each end. That’s a lot of potential failure points, and cable faults can appear as several different kinds of problems.
An unbalanced cable with an open signal lead almost always causes a complete loss of signal, but if one signal lead of a balanced cable opens, the results are less predictable. Depending on the configuration of the source and destination equipment, you might lose the signal entirely, have a substantial loss of level and low frequencies, or just experience a 6 dB signal level drop—which could go unnoticed for a while.
A shorted cable can also cause varied symptoms. With a short between the signal lead and shield of an unbalanced cable, you usually lose the signal. But with a “high resistance” short circuit of a few ohms (like if one fine strand of the shield has worked loose and is barely touching the signal lead) the result may be a drop in signal level and some noticeable distortion, but not a complete signal loss.
A short between the two signal leads in a balanced cable will usually result in no signal. But a short between the shield and one of the signal leads unbalances the connection. This might cause an increase in hum or noise pickup, a drop in signal level, or it might not audibly affect anything at all.
1/4" phone jacks are very common these days, and their quality varies widely. While they all work fine when they’re new, contacts can lose their springiness with age. After a while they won’t grip a plug snugly. And even the best ones are subject to the evils of dust, dirt, and oxidation.
A jack-to-plug contact usually doesn’t fail in a way that causes complete signal loss. More often the connection will be intermittent, causing the signal to come and go. A high-resistance contact such as caused by dirt or corrosion can cause the contacts to act as a semiconductor, resulting in distortion along with a drop in signal level.
If you use normalled patchbays, remember that there are switch contacts inside that make a connection when no patches are inserted. Those normalling contacts can get dirty too. Distortion and crackling in a signal that passes through normalled patchbay jacks means it’s time for a patchbay cleaning.
Isolating the problem
Short of a major disaster like a lightning strike, most troubles can be localized to a single point: a cable, a connector, a stand-alone unit, or one channel of a multi-channel device. Your first task is to find out what has failed.
You may fix the problem in the process, but if you don’t, at least you’ll know where it lies. Replacing a bad cable is simple once you find it. Repairing a digital signal processor is usually a job for an authorized service station.
Most problems can be stated simply: you have an input but no output, or an output that sounds wrong. Logical troubleshooting means tracing a signal from source to destination and determining where it gets lost. Most of the time you can do this without any special test equipment, using what you already have in the studio.
You just sang a killer vocal. Hitting playback to bask in your glory, you hear nothing but your backing tracks. What happened? And will it happen again? Time for a little troubleshooting.
For the sake of this exercise, let’s say you have a typical 8-track studio setup with a few pieces of outboard equipment and a patchbay. The multitrack recorder might be a computer, and the mixdown recorder might be a DAT, cassette, or CD-R. You could have direct connections rather than going through a patchbay, but the techniques are the same in any case.
Reading the meters
Your system has several built-in tools for monitoring signal level, or at least checking for its presence. An indication on the recorder’s record level meter shows that the signal got from the mic to the recorder. As an old-timer, checking meters as I work is second nature to me, but today the only meter available may be buried under a couple of layers of software screens. Don’t ignore it as a test tool, however.
With the recorder set to Input Monitor mode (most DAW software also provides this function if you know where to find it), speak into the mic and watch the record level meter. A normal signal level means the chain is okay up to the recorder and the problem lies either in the recorder itself or in the playback chain. If there’s no signal getting to the recorder, it’s time to take a look at the input signal path.
What’s in the signal path? There’s the mic itself, the mic cable, preamp (which may be outboard or in the mixer), and the cable from the preamp to the recorder. If there’s a patchbay there will be additional cables and normalling contacts or patches in the path. You can start troubleshooting at either end or even in the middle, but you must be systematic or you’re likely to miss something.
One troubleshooting procedure that works well is to use an alternate signal path and see what works. Instead of using the mic preamp as the source, temporarily connect another signal source (a keyboard or maybe a CD player) directly to the recorder’s input. If that tickles the meters, you know the recorder is working and the problem is between the mic and the recorder input.
Try patching the mic preamp output to a mixer input or directly to the monitor amplifier (watch out for feedback!). If you then have signal, you’ve narrowed the problem down to the cabling between the mic preamp and the recorder, either a cable itself or a patchbay jack or contact. If you still don’t have signal, check the mic cable, the mic, or the preamp.
When substituting signal sources it’s important not only to reroute the signal, but to do it using a known good cable. Connecting a good keyboard to the recorder through the existing preamp-to-recorder cable (which could be the bad apple) when you’re not sure that the recorder is working properly could be misleading. If you still don’t see record level you don’t know if it’s the recorder or the cable.
After you’ve verified that the recorder will indicate the presence of a signal, you can start putting your input signal chain back together piece by piece and you’ll quickly locate the bad link.
If everything is okay up to the recorder, then the problem must lie on the playback side. Again, the recorder’s meters are the first place to start. Switch to Repro Monitor mode and watch the failed track’s meter when playing the tape to see if it’s indicating the presence of a signal on tape. If it’s not, load up another tape with something on that track and check for playback.
If the problem track doesn’t play back with your known good tape, take another look at the meters. If the meter indicates that there’s something there and you’re not hearing it, you have a problem with the playback chain and it’s time to do some more troubleshooting, piece by piece. If the meters still don’t indicate, it’s time to send the recorder to the shop.
Try connecting the track output directly (with a known good cable of course) to an alternate input—the tape return on a different channel, a different line input, or auxiliary return…anything that you can route to the monitors. If you then can hear playback from that track, start putting the normal path back together a link at a time until you find what breaks the chain.
Another approach is to work the other way: substitute your keyboard (as a test source) for the tape playback. If you can hear that you know the console is okay.
If you can’t, try moving it to a different tape return or line input. You might have a console problem or a wrong button pressed. Moving the keyboard back along the chain toward the tape deck one link at a time will verify all the cables and connectors in the path or identify the bad one.
Those pesky intermittents
Not all cable and connector problems are solid failures. And sometimes a problem just goes away by itself. Those are the nastiest because you have to convince them to fail when you’re looking for the trouble, not when you’re trying to get some work done.
A poor solder joint can cause distortion or crackling as it alternately makes and breaks contact. And a cable shield that’s been flexed so many times that it’s no longer solidly connected to a ground terminal can cause hum or noise to appear intermittently in a normally quiet system.
The common approach to locating an intermittent cable or connector is to tug and replug. Sometimes try as you might you just can’t get an intermittent to fail. Don’t forget about it, though. It’ll be back again some day, and your troubleshooting luck might be better then. In the meantime, pulling each plug in the guilty chain and giving its jack a shot of contact cleaner spray before reconnecting is good preventive medicine.
I’ve been talking tape decks and meters as if they were real, but with a computer-based DAW setup the same techniques apply. All recording programs and audio interfaces have some sort of metering, though you often have to take an extra step or two to make it visible. And you can easily verify a recording by looking at a track’s waveform.
Unless you’re very watchful when new software gets loaded, drivers and setups have a way of getting changed without your knowledge. When troubleshooting points to the recorder and the recorder is a computer program, the fix may be to reinstall drivers or other software. That’s sometimes a drastic measure, but sometimes you just have to give it a try.
Wall warts don’t last forever. If a unit has failed totally (no lights or displays as well as no output) and it’s powered by a wall wart, that could be its problem.
A common failure mode is a break in a wire right at the connector or the lump, where bending stress is greatest. You might find that by pushing and wiggling the cable right at the point where it joins the connector or power unit you can bring a unit back to life intermittently. A break at the connector end can be repaired by cutting the cable short of the break and replacing the connector with a new one. A break right at the wart end usually means a replacement. The power jacks on the equipment have a way of loosening up after a few years too.
Open heart surgery
While most problems can be traced to bad connections, now and then a piece of real hardware dies. More and more hardware is less and less user serviceable, but there are still fuses that can be replaced or socketed ICs that can be reseated.
If you’re handy, remove the cover and look around. If you see ICs installed in sockets, it never hurts to press them down to refresh their contacts. Often fuses are mounted in clips inside the equipment, or even in sockets molded into the detachable power cable jack, rather than in panel-mounted fuse holders. They’re easy to replace once you find them.
When it comes to working under the hood, the usual warnings about shock hazard and voiding warranties apply. Be sure the unit is unplugged before you remove a cover. Examine the case screws carefully. Some that look like common Phillips head are actually Reed and Prince, a cross- slot with a different taper. Screws appearing to have Allen socket heads might actually have Torx or square sockets. If you strip them out, you might have trouble disassembling or reassembling the gear in the future.
And some manufacturers employ “secure” screws that require a special driver, to keep people like us from messing with the inner workings. If you’re going to try a DIY repair, at least have enough respect for the manufacturer to use the correct tools.
If you’re inclined to so some internal troubleshooting, get out your multimeter and start looking at power supplies first. Power supply problems generally cause a total failure—although if the power supply provides multiple voltages, power might be present to run lights and the display, but not the audio circuitry. The 11/98 and 12/98 articles in this series can give you some guidance in troubleshooting the power supply.
If it ain’t broke
You’ve surely heard the expression ‘If it ain’t broke, don’t fix it.’ A corollary when it comes to troubleshooting is ‘If you don’t fix it, it’s still broken.’ Most problems are easy to fix if you don’t go around in circles solving them.
I’ve given just a couple of examples here, but a systematic approach works every time. May all your failures be simple ones.
Mike Rivers can’t troubleshoot your studio for you, but he might be able to answer a question or two. Email him at firstname.lastname@example.org.