Troubleshooting With a Cool Head
By Mike Rivers
It happens to everyone at some time or other: Something was working fine the last time you used it but it’s not working now. In the good ol’ days, most recording engineers were pretty good technicians or there was a maintenance technician on staff or on call. Troubleshooting was all in a day’s work.
That’s rarely the case today. More people are coming to recording and live-sound engineering from a nontechnical background. Furthermore, today’s equipment is more complex in function, design, and construction than it used to be. Going behind the rack, finding a cold tube, and swapping it out to get the session running again just doesn’t work any more.
Most modern studio equipment is highly reliable. Solid-state components have a very long lifespan unless they overheat or get zapped because of an upstream problem. Even low-cost gear rarely fails as a result of poor solder joints or broken wires. Quite often, a problem that pops up is the result of something external, often as simple as a bad cable or partially unplugged connector. But with so much of today’s gear being less dependent on basic electronics and more dependent on computers and software, it’s easy to get lost trying to find where a signal is going astray.
With a cool head and a logical approach, you can solve most such problems and get back to work promptly. The first step to solving a problem is to isolate it. Let’s look at common failure points and how to locate them.
What’s The Problem?
Some problems (though not necessarily their solution) are apparent: Quality gear suddenly sounds bad, or an incomprehensible error message pops up on the device’s front-panel display or on your computer screen. Many faults that yield such symptoms don’t have unique solutions and require troubleshooting tools and techniques beyond the scope of this article. Problems that can usually be solved quickly fall into two broad classes: Either something’s obviously dead, or you hear something that you know isn’t right, such as distortion, hum, an unusually low or high output level, or extraneous noise.
Most troubleshooting techniques are obvious, but the trick to solving a problem is to eliminate the possible causes in a logical manner. Here’s a very simple example: If a problem shows up after you’ve made a change—moving or replacing a cable, adding a new device to the signal chain, or updating software—undo what you did and see if the problem goes away.
Are the electronics plugged in? Is the power switch on? Am I being condescending? No, not intentionally.
Everything used to have an on/off switch and a pilot light, and we became accustomed to turning something on before using it. With today’s cost-conscious designs, if a piece of gear consumes fairly little power, the on/off switch, often along with a pilot light, is less common. The presence of primary power isn’t always as obvious as it used to be. (Some companies still help you with this. For instance, virtually all PreSonus hardware products, including Eris and Sceptre studio monitors and StudioLive AI-series PA speakers, have front-panel power indicators or sync lights or lighted meters that serve as power indicators.)
The “green” movement may change this, but in your studio or PA rig, you probably have several pieces of gear plugged into a common power strip with a single power switch. Things are always getting moved around, and it’s easy to inadvertently dislodge a power connector (or any connector for that matter). Captive power cords are usually pretty reliable but with a detachable IEC power cable, something might have snagged the cable and pulled it far enough away from the chassis connector so that it’s no longer making contact. Check both ends of a removable power cable. Wall warts are notorious for falling out of power strips in the back of the rack or in a dark corner of the studio, and few of them have connectors that lock securely into chassis of the equipment they’re powering.
More than once I’ve spun my wheels tracing out an input path to a signal processor whose only visual indication that it’s working is a signal-present LED, only to find that its power cable had worked loose. One of these times, I’ll remember to check that first. You should, too.
Oops, Wrong Button
Is a mixer channel muted, or not assigned to the output you intended? Are you trying to record on Track 4 but the signal is actually going to Track 3 because a pan pot is turned the wrong way or you forgot to move a patch cable? Is the recorder or DAW switched to Input Monitor when you’re expecting to hear playback? Is something patched into the signal path that’s turned off or set incorrectly?
This is obvious stuff of course, but don’t ignore it – it only becomes obvious once you find it. Smack your forehead and move on.
Cables and connectors are probably the most common trouble sources, especially in studios that rely on a lot of hardware. A typical small recording setup with just one modest patch bay involves 96 patch points (48 in front, 48 in the rear), each containing two or three wires soldered or crimped at each end. That’s a lot of potential points of failure, and it doesn't include the cables.
Cable faults can cause different kinds of problems.
In a DAW-based system, many cables and patch points are replaced by software, and an unchecked box or an incorrectly assigned input or output isn’t always as obvious as a missing or partially unplugged cable.
Busted, Disgusted, and Can’t be Trusted
First, check your connections and your signal routing to be sure that your signal isn’t hitting a dead end or taking a detour to where you’re not looking for it.
An unbalanced cable with an open signal lead can result in a complete loss of signal. A broken shield connection can also cause signal loss because you no longer have a return path for the signal, creating an incomplete circuit. But the circuit might be completed in a roundabout and less dependable way through the chassis of two pieces of gear screwed into the same rack, or by power-cord safety grounds plugged into the same outlet strip. This may not be a problem until you use that cable for something else—or it could result in increased hum or noise.
Bear in mind, too, that a broken cable doesn’t always stay broken. A cable that’s been flexed or yanked too often can develop an intermittent break. If you suspect a cable, tug or flex it where the cable emerges from the plug and you might hear your problem come and go.
If one of the two signal leads of a balanced connection opens, the results are less predictable. Depending on the circuit configuration of the output and input that you’re connecting, you might lose the signal entirely, have a substantial loss of both level and low frequencies, or perhaps experience a 6 dB loss in signal level, which could go unnoticed for a while.
A shorted cable can also cause various symptoms. With a short between the signal lead and shield of an unbalanced cable, you’ll usually lose the signal. But with a “high resistance” short circuit of several ohms, for example, if one fine strand of the shield braid has worked loose and barely touches the signal lead, the result may be a drop in signal level along with some distortion, but not a total 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, depending on the configuration of the balanced output, might not noticeably affect anything at all.
An improperly wired cable can cause some unusual symptoms. If two units are connected using a balanced cable with the tip and ring wires (or pin 2 and pin 3 on an XLR) crossed, depending on the application, you could get no signal at all, a low signal level, reversed polarity (“out of phase”), or left and right channels reversed. If it’s an “insert” cable with a two-circuit (tip-ring-sleeve, or TRS) plug on one end and two “unbalanced” plugs on the other end, the plug that you think is the send (going to the input of the inserted device) could actually be the return, and vice versa. Just swap input and output plugs to fix this one.
There are several different ways to interconnect balanced and unbalanced inputs and outputs. If an incorrectly wired cable is used, some devices won’t work or will give unsatisfactory results. In this case, there’s no one correct way for every pair of devices. You may need to experiment with rewiring or adapters, but this is a problem that usually occurs only when installing something new. Check the wiring before packing up that “great bargain on eBay” that you’re trying to put to use.
Quarter-inch phone jacks are very common, and their quality varies widely. While they nearly all work fine when they’re new, jack contacts can lose their springiness with age and will cease to grip a plug snugly, particularly if it’s a jack that normally has a plug “living” in it. Even the highest-quality plugs and jacks 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 becomes intermittent, causing the signal to come and go.
A high contact resistance resulting from dirt or corrosion accumulating on the plug or jack can cause the connection to act as a semiconductor, which may cause distortion or static-like crackling, as well as a drop in signal level. This problem can also occur without a plug at all if you have a signal going through a normalled patch bay jack or an insert jack that hasn’t been used in a while. In this case, the “semiconductor” is formed by the normalling contacts, which should be closed and passing the signal straight through if there’s no plug inserted in the jack. A shot of contact cleaner worked in by inserting and removing a plug several times usually fixes this problem.
Normalled patch bay jacks and channel-insert jacks (which nearly always have the send and return normalled) have mechanical switch contacts built into the jack. These contacts make a connection between input and output when there’s nothing plugged into the jack. Normalling contacts can get dirty, particularly if they’re not used frequently. This most often is a result of either removing a plug that’s nearly always inserted, or inserting a plug into an infrequently used jack and then removing it. Distortion and crackling where a normalled jack is involved means it’s time for a cleaning.
Mixers and channel strips often have insert jacks that you’ve never used, and you may not even realize they are there. One example is an insert jack ahead of a subgroup bus. A problem could exist for a couple of years without your knowledge until you plug a compressor into the subgroup insert.
Isolating the Problem
Short of a major disaster, like a lightning strike or a flood, most troubles can be localized to a single fault: a cable, a connector, or a single stand-alone unit. Your first task is to find out which part of the system has failed. Here, “system” means everything that’s between the input (microphone) and output (loudspeaker).
Start with the big pieces before opening up a case or asking on the Internet “Does anyone have a schematic for…?” Replacing a faulty cable is simple once you find it. Repairing a faulty digital signal processor is usually a job for the manufacturer or an authorized service station.
Most problems can be stated simply: You’re certain that you have input (make sure you do!) but no output. 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, along with your ears and eyes.
Read The Meters
Your system has several built-in tools to check for signal presence and signal level. An indication on the recorder’s record-level meter will tell you that the signal got from the mic through the preamp or mixer and to the recorder. As an old-timer, checking meters as I work is second nature, but today the only meter available may be just one or two LEDs or a screen buried under a couple of layers menus. Don’t ignore it as a test tool, however.
With the recorder set to Input Monitor mode (most DAW software also provides this function – it’s often called something like “tape monitor mode”), 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 with 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. No signal at the recorder suggests that the recorder is defunct or you need to look backward along the chain toward the microphone.
You have to consider the mic itself, the mic cable, and the mic preamp, which might be outboard, in the mixer, or integral with the DAW audio I/O interface. Then there’s the cable between the preamp output and the recorder or DAW interface input. If there’s a patch bay, that adds cables and normalling contacts to 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 of the quickest ways to troubleshoot a system problem is to simplify the system by removing as much from the chain between the primary source and final destination as possible.
If you have a few pedals between your guitar and your amplifier or DI input, plug the guitar directly into the amplifier input or DI. If that works, then start adding the pedals back in one by one until it quits working. You then have narrowed the troubleshooting job down to either the pedal or the cable connecting it.
The same technique works for chains that consist of a mic feeding a preamp, then a compressor, then an equalizer before hitting the input of your DAW interface. Another simple troubleshooting technique is to substitute an equivalent path. If your mic connected to channel 3 isn’t working, plug it into channel 1. Obvious, sure, but I’m surprised at how many people don’t try that before asking for help.
To further simplify the system, use an alternate source. Instead of the mic and preamp, temporarily connect another signal source (a keyboard or CD player) directly to the recorder or interface input. If that tickles the meters, it suggests that the problem is between the mic and the recorder input. If you still don’t get a reading on the meter, then the device with the meter is the likely culprit. Try patching the mic preamp output to a mixer input or directly to the monitor amplifier. (Watch out for feedback!) If you still don’t have the mic signal, check the mic cable, the mic, or the preamp. If you have the mic signal, you’ve narrowed the problem down to the cabling between the preamp output and the recorder: either a cable or a patch-bay jack or contact.
When substituting signal sources, it’s important to use known good cables. You’re trying to establish what works and what doesn’t, and a good cable is part of your test equipment. If you use a bad cable to connect a good keyboard to a mixer, you might assume that the mixer is faulty when it’s actually your test cable.
Once you’ve verified that the device you’re testing with is capable of indicating the presence of a signal, you can start putting your input chain back together piece by piece. You’ll quickly locate the faulty link.
Troubleshooting the Recording/Playback System
If everything is okay up to the recorder, the problem could be on the recording or the playback side. Again, the meters are your first troubleshooting tool.
Switch to Repro Monitor mode, start playback, and watch the faulty track’s meter to see if it’s indicating the presence of a signal coming from tape or disk file playback. If it’s not, load up another tape with something on that track (or open another file) and check for playback.
If the problem track doesn’t play back with your known good tape or file, take another look at the meters. If the meter indicates that there’s something there, and you’re not hearing it, the problem could still be in the recorder—the meter isn’t always directly across the output—or there’s a problem with the chain following the recorder output.
Try connecting the track output (with a known good cable of course) directly to a different input: the tape return on a different mixer channel, a different line input, an auxiliary return—anything that you can route to the monitors. You can connect the output directly to the monitor amplifier or a powered speaker but be sure the volume is turned down when you start the playback. If you can then hear playback from that track, start putting the normal path back together one piece at a time until you find what breaks the chain.
By the way, you can plug a set of headphones into just about any ¼-inch output jack and hear something if there’s a signal present. You’ll probably hear it in just one ear unless you’ve plugged into a headphone jack or a jack fed from a symmetrical output (both tip- and ring-driven), but it’s a quick way to check for the presence of a signal.
In a software-based system, a playback problem could be a driver gone astray or software corruption. You’ve probably rebooted a few times already, so maybe it’s time to reinstall a driver or try using a different DAW program.
We’ve been working mostly forward in the signal chain, but sometimes it’s productive to work backward. Start with a known good signal source like a keyboard or CD player, connect it to the monitor or PA amplifier input, and verify that you get sound. Then start moving it back piece by piece until you lose the signal.
Those Pesky Intermittents
Not all cable and connector problems cause definite failures. Sometimes it seems that a problem just goes away by itself, but you can be sure that at some time, it will return to haunt you. Intermittent problems can be the nastiest of all because you have to convince them to fail when you’re looking for the fault, not just when you’re trying to get some work done.
A poor solder joint can cause intermittent distortion or crackling. A cable that’s been flexed so many times that its shield or a conductor is no longer solidly connected can cause intermittent hum, noise, or total loss of signal in a normally quiet system.
The most common approach to locating an intermittent cable or connector is to tug and wiggle the cable and unplug and reconnect the plug. Sometimes, try as you might, you just can’t get an intermittent to fail. Don’t forget about it though. It’ll return 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.
A lot of modern equipment makes use of ribbon cables for internal connections. There may be 20 or more pin and socket connections for each cable, and it only takes one bad contact to cause a problem. In addition to the plug-to-socket contacts, most ribbon cables use insulation-displacement-type connectors, which aren’t soldered to the wires but depend only on the integrity of a mechanical clamp to maintain contact between the wire and the connector. Connector sockets can get weak, pins can get corroded (even gold-plated ones), and insulation displacement contacts can work loose.
Still, if you’re not afraid to crawl under the hood, many problems have been solved by removing a ribbon cable, giving the sockets a quick shot of contact cleaner, and then working the cleaner on to all the contact surfaces by plugging and unplugging the connector a few times. Most ribbon connectors are keyed so you can’t put them together backward—but some aren’t, and you could compound the problem by connecting a ribbon cable backward, so take note of the connector’s orientation before you disconnect it. There’s often a different colored stripe on one edge of the ribbon to help you orient the cable correctly.
Wall Warts and Other Power Supplies
If a unit appears to be totally dead (no lights, meters, or screen displays, in addition to no output), and it’s powered by a wall wart, the power supply could be the problem.
External power supplies are usually fairly cheaply built and don’t last forever. A common failure mode is a break in the wire at the chassis connector or right where it comes out of the transformer lump. These are points where stress is greatest. You might find that by pushing and wiggling the cable at one of those stress points, you can bring a unit back to life intermittently.
Since these power supplies usually can’t be disassembled without a hacksaw and a good guess as to where to cut it apart, a break right at the wart end of the cable usually calls for a replacement of the whole assembly. A break at the connector end can be repaired by cutting the cable behind the break and replacing the connector with a new one. If it’s a DC wall wart, before you solder on a new connector, be sure you know which terminal is positive. One wire usually has a white or silver stripe Use your multimeter to check the dud for continuity of whichever wire is still good (rarely will both break at once), and use that information to identify how to wire the replacement connector.
A word of warning: Coaxial power connectors come in about a dozen different sizes, not only different in outside diameter but in inside diameter, as well. Be sure to get the correct replacement. Radio Shack stores have a measuring jig for these connectors (if they can find it) that will help you to identify the proper replacement.
The power jacks on the equipment have a way of loosening up after a few years, too. They can be replaced but it’s not always easy.
I’ve mostly been talking about tape decks and VU meters because it’s easy to understand real hardware. A computer-based DAW setup, while lacking those physical parts, performs the same functions, so the same troubleshooting techniques apply.
All recording programs and computer audio interfaces have some sort of metering, though it may be minimal, and you may need to make the meters appear with a mouse click or menu selection. You can nearly always verify that something was recorded by looking at the track waveform display, though if nothing’s there, without looking at an input-level meter move, you can’t be sure that the signal arrived at the recording input.
Testing the Hardware
Digital connections aren’t as friendly to test equipment as analog connections; you can’t plug headphones into a FireWire or ADAT Optical output and hear something. When troubleshooting a computer-based system, it’s often tricky to determine whether a problem lies within the computer or with something external.
If you’ve eliminated problems with external hardware and cables, you’re still left with determining if the computer-related problem lies with the computer hardware itself (a flaky memory module, for example), the operating system, related software components like drivers, the application program, input or output connections, or the user (that’s you). Troubleshooting computer hardware is beyond the scope of this article but software is available that will test most of the major components, although some tests can take quite a bit of time.
Software and Drivers
All too often, a problem turns out to be that a setup parameter, such as an input-to-track assignment, was inadvertently changed, and you simply didn’t notice.
Sometimes installing or updating a program can make changes to the system configuration that cause something that was previously working to stop working. Consumer “multimedia” software such as media players or games don’t have much respect for sophisticated multitrack audio recording applications; they try their darndest to assure that something will come out of the loudspeaker when you start the game or movie.
If you’ve lost the audio playback from your DAW, think about software you’ve installed recently. A new program may have changed the setting that sends audio to your high-priced sound card, diverting the audio stream to the built-in sound card that it expects every computer to have.
In general, software doesn’t break, but things can be changed without your knowledge (or maybe you just forgot what you did last time you were working). Files on disk can become corrupt but this rarely happens spontaneously. Scrambled or lost data is usually the result of another problem that needs to be fixed. There may be an impending disk drive failure, a loose or dirty disk drive cable, faulty memory, or a malicious program that somehow crept in.
“Get the latest drivers” or “get the latest version of the program” is one of the most common pieces of advice when your computer-based DAW stops working. This is definitely a valid recommendation when installing a new program or a new piece of hardware. However, if everything had been working fine before the trouble started, a software update may or may not fix the problem, and it may cause a new problem.
It may be helpful to reinstall a driver or a program in case something has dropped a bit here or there. As a hedge against this, keep a copy of the current versions of all your installations so you don’t need to start from the CD that came in the box or use a newer version than you’d been using.
Open Heart Surgery
While many problems can be traced to bad connections, now and then the problem will be a real hardware failure. Much of today’s hardware is not user serviceable, but there are still fuses that can be replaced and internal connectors or socketed ICs that can be reseated.
Most devices these days have a sticker or a warning in the manual about lethal voltages and no user serviceable parts inside. This is reinforced by the popular belief that even loosening a cover screw will void the warranty. Their lawyers don’t want you to get hurt working on their equipment.
Use common sense. The only lethal voltage in most solid-state gear is where the AC power line comes into the box. Unplug the unit, and you’ve eliminated the lethal voltages. You may need to power it up with the cover open in order to check a repair you’ve made, but once it’s open, you can see where not to stick your fingers. Just be careful.
Tube equipment is different. There are several hundred volts running around inside, and you really must be careful what you touch if it’s open and powered up. Also, power amplifiers have large filter capacitors as part of the power supply. While solid-state power amplifiers rarely operate at higher than 40 volts inside, those capacitors don’t always fully discharge when you turn the unit off. While the voltage won’t kill you, you can pull a substantial spark if you accidentally short circuit across one, and this can startle you enough so that you might tear a piece of skin getting your hand out of there faster than you ever thought you could move. If you wear a ring, take it off. And be careful with your screwdrivers.
You’ll rarely void a warranty by looking around; just don’t break anything while you’re in there. Take advantage of the warranty if it’s still in effect, and don’t worry about voiding a warranty that no longer covers the unit.
With the safety precautions understood, if you’re handy with tools, and I haven’t scared you away, unplug the unit, remove the cover, and look around.
Examine the case screws carefully. Some that look like common Phillips head are actually Reed and Prince, a cross-slot with a different taper. A Phillips screwdriver will work if they’re not too tight, but it might slip out if you need to apply a lot of torque, bungling up the screw head. What look like Allen socket screw heads might actually be Torx or some other “secure” type that requires a special driver in order 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.
It’s a good idea to have a few containers for the screws that you remove, particularly if they’re of different diameter or length. A muffin pan is great for this, as are seven-day pill containers and breath-mint tins.
Loose ICs, Blown Fuses, and Powerless Power Supplies
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, rather than in panel-mounted fuse holders. They’re easy to replace once you find them, though occasionally a fuse is soldered to a circuit board. While fuses occasionally die of old age, most of the time, when a fuse is blown, it’s because something else is wrong, so the replacement will blow, and you need to find out why.
If you’re inclined to do some internal troubleshooting, get out your multimeter and start checking voltages at the input (AC) and outputs (usually DC) of the power supply. Equipment must meet safety standards and be certified in order to be sold in the U.S. or Europe, so there’s going to be a reasonable amount of protection from electrical shock hazard, even with the case open.
In fact, it may be so “safe” that you’ll have difficulty measuring the AC input to a power supply. That’s the first place to look for a problem when the unit is dead. Power-supply problems typically result in total failure, though if the power supply provides multiple voltages, voltage might be present for the lights but not the audio circuitry or vice versa, or phantom power may be missing. A voltage regulator component may have failed, causing an incorrect voltage, or a filter capacitor may have failed, causing excessive ripple on the DC output. You can check for ripple by switching your voltmeter to measure AC voltage and seeing whether there’s any voltage at a power-supply output.
Some devices, particularly those with balanced analog inputs, operate internally on both positive and negative voltages with reference to ground. It’s fairly common, when bipolar (typically plus and minus 15 volts) DC power is required, to use an AC wall wart, with a bridge rectifier and the power-regulating circuitry inside the box.
Often there are separate power supplies (though they may be in the same enclosure) for analog and digital circuitry. Sometimes power-supply inputs are fused, sometimes outputs, sometimes both. (Check for a dedicated phantom-power fuse.) Fuses are best checked by removing them (power off first!) and measuring for continuity.
Don’t forget to check the batteries. If you find any corrosion in the battery compartment, clean it up. Unless it’s really bad, water on a cotton swab is safe and usually works.
If it Ain’t Broke
You’ve surely heard the expression “If it ain’t broke, don’t fix it”. A corollary is “If it’s broken, and you don’t fix it, it’s still broken.” Many problems are easy to fix if you don’t go around in circles solving them. Some are really pesky, require specialized test and service equipment, and are best left to the manufacturer or a competent service shop. I’ve given just a couple of examples here, but a systematic approach works every time. May all your failures be simple.
Indispensable Troubleshooting Tools
Here's a short list of tools you need to keep handy.
- At least one good cable of each type that you use
- A multimeter (VOM). It need not be an expensive one, since you’re not calibrating anything; you just want to be able to test for voltage and continuity. Analog or digital will do. Radio Shack and Home Depot have suitable ones.
- Hand tools: You may need to open a case or open a connector.
- A soldering iron, if you dare. Practice repairing cables before you start replacing integrated circuits!
- Cleaning supplies: a spray can of an electronic-grade contact cleaner such as Caig Pro Gold, and a can of pressurized clean, dry air.
- A dependable but simple signal source like a CD player or MP3 player
- An adapter from a ¼-inch stereo (TRS) plug to a ¼-inch mono (TS) plug. Plug your headphones into this, and you can use them as a signal tracker to check for a signal at nearly any ¼-inch output jack. Radio Shack #274-360.
- An assortment of connector adapters or adapter cables (a cable with different connector types on each end)
- Mini stereo: 2 x ¼-inch (for your portable player output)
- XLR-to-¼-inch TS and TRS, with both genders of XLR. Note that there are two common ways to wire ¼-inch-to-XLR.