WHEN YOUR AMP STOPS WORKING- TROUBLESHOOTING TECHNIQUES

This month we will talk about what to look for when your guitar amp doesn't work. Sometimes there may be a simple easily solvable explanation or sometimes there is a catastrophic failure inside. I find a lot of people have a poor understanding of how an amp works and many do not understand how to operate its functions beyond plugging a guitar in and turning up the volume. Plus, under the pressure of a gig that is about to start, even the technically savvy can be thrown by a combination of anxiety and a dark stage.

When you get in a situation where your amp is not working, there are ways for you to analyze the situation and see if there is something you can do about it. I will outline some things you can try which will tell you whether you can get things working or if you need a trip to the repair center. These are all things I have actually seen be problems for people. We'll discuss this as if you are setting up for a gig and experiencing a failure.

FOR A NO SOUND PROBLEM

First- determine if the amp is powered on. Is the wall power outlet actually live? Something very easy to overlook. Plug something else in to the outlet and see if it works. Is the amps power indicator possibly not working? On a tube amp, look at the tubes to see if they are lit up. Oftentimes the bulb for the pilot light has come loose or is blown and the amp is really on. Another possibly overlooked item is the fuse. Disconnect the power cable from the wall outlet, take out the fuse and examine to see if it is blown. The fuse is a protective device and is there to keep the amp from catching on fire when there is a short inside the amp capable of drawing enough power to cause a fire. Therefore if the fuse is blown it's a good chance a new fuse will blow too and it is time for a trip to the service center, but there are also times a power surge or similar event will blow the fuse and if you replace it all is well again. Sometimes it is not apparent where the fuse is located. A minority of amps have their fuses inside the chassis and require opening up the amp to get to it. But if you don't see an independent fuse holder on the amps front or rear panel look at where the power cable plugs in. There may be a little door that can be pried open and you will find the fuse hidden inside. The reason this is done is to make it necessary to remove the power cord before accessing the fuse so there is no possibility of being shocked.

Some amps also have the ability to be used with different line voltages so the amp can be use in the many countries around the world that use a different voltage than 120 volts. If you see such a switch make sure it has not inadvertently been switched off of 120 volts to 240 volts etc. If it has been switched it will not hurt the amp at all but will either render it not working or working and not putting out much power. I saw this happen twice in just the last week.

Once it has been determined that the amp is on, let's double check some obvious things. If you are using a head and cabinet re-verify that your speaker cable is plugged into the correct speaker jack on your amp. Many amps (especially Fenders) have a main speaker jack and an extension speaker jack located right next to each other. Plugging a single cabinet into the extension jack with nothing plugged into the main jack will give you no sound or very little sound. If you are in the correct jacks, have someone play the guitar while you wiggle the cable at both the head and speaker cabinet jacks to see if it comes on even for a brief second. If it does try another cable to see if it is the cable or the jack. Same for if you get no sound, eliminate the variable of the cable by trying a known good one. Still no sound? Try another cabinet. Anything on hand will do. A bass or PA cab is fine if no other guitar cabs are around. We just want to hear if there is sound. If you are using a combo amp, take a look at the speaker terminals. Has a wire been pulled off a speaker terminal from storing all your pedals and cables back there on the way to your gig?

I always recommend to reduce things down to their basic elements. If you have a pedal board hooked to your amp, remove it and see if it comes on. Try a different guitar and cable. Don't be sure of anything. You know your guitar worked last night when you used it on a different amp, but that doesn't mean it is working now. Don't make an assumption that it has to be the amp. What counts is what is happening now. I get gear in my shop all the time because people make assumptions. If no sound is coming out of a speaker cabinet people assume it is broken, yet they never think about if the amplifier driving it is broken that is why there is no sound.

Next let's go to the front panel. Are indicator lights for various functions illuminated and do they change when there respective buttons are pressed? This is important. Indicator lights that are staying on or off and not changing with the switches are a possible sign of failure inside the amp's power supply.
Now, check your front panel control settings. Many of us are used to leaving the dials set and never changing them, so it may not occur to you that a dial such as a master volume or gain has been inadvertently turned off. I fixed an amp for someone not long ago who returned several days later screaming at us about how much he paid to have the amp fixed and now there was no sound at all coming out. It made my day to plug in a guitar in front of him and turn up his master volume control from zero. I also had a situation the other day where I was called onto the sales floor by a sales person who was demonstrating a tube amp for a customer. They both were convinced the amp was broken. I walked over and flipped the standby switch on the front panel and the amp came roaring on. Modern amps are complex. There are many features and many ways to go wrong.

Move on to the rear panel. Although the rear panel of an amp may not contain as many controls as the front panel, there are still places to go wrong. Many times the standby switch is hidden( I mean positioned) here and we know where that can lead. Some amps have their effects loop jacks located here. If there is a bypass switch associated with a series effect loop the send and return jacks may not be connected to each other internally so signal can flow from the send to the return jacks when no effects are plugged into the jacks. Therefore if the loop is switched on and you are not using effects connected to the loop no sound will come out of the amp. Mesa Boogie confuses this problem further. On many of their amps the master volume and solo volume will only work if the loop is switched on. What does this have to do with the effects loop? Had a guy the other day who brought in a Boogie for just that reason. Turned the loop switch on and all was well again, but he had suffered through a whole gig without those functions. Parallel effect loops can cause a similar problem. Some of the old Marshall Valvestate amps had a mix control right on the front panel. Dial it to the right and no sound comes out when nothing is hooked to the loop. I can't tell you how many of these came in for " repair" when these amps were popular.

Check for a tube that has come loose or fallen out. Combo amps are notorious for this because the tubes hang upside down. And here's a tip for Peavey Classic 30/50 players. The tubes in those amps have their heaters wired in series. If one tube comes loose they all turn off. The long skinny EL84 output tubes hang upside down with a very anemic clamp and tube socket holding it place. The chances of one of them moving out of place on the way to your gig are higher than the tube staying in place.

Another cause of no sound coming out of a tube amp is a blown HT fuse. This fuse is in the power tube circuit and will likely be on the rear panel next to the main fuse. It is there to protect the other components in the output stage especially your output transformer from damage in the event of a shorted tube. If the HT fuse is blown everything will look right about the amp but no sound will come out. I will reiterate a point here I have made in many of my previous articles. Just because a tube is lit up does not mean it is working. A tube has several voltages inside it and the only one that gives visual evidence of its presence is the heater voltage. Yet all voltages must be present to produce sound. The voltage that is connected to the fuse is obviously not connected to the tube if the fuse is blown. If you come up against a blown HT fuse there are some steps you can take that may get you running. First look at your power tubes. Do you see any cracked glass or a tube where the top has turned white (near where you spilled your beer into the amp). Did you notice a specific tube arcing or the gray metal structure inside the tube glowing cherry red right before the fuse blew. All of these are indicators of a blown tube.The safest fix for this is to replace the fuse and put in the spare set of output tubes you always have with you. You do carry a spare set don't you? If you don't have a spare set and it is a four output tube amp you can pull out the known bad tube and one other to get the amp working. You won't be as loud as four tubes are but you will be louder than no sound at all. Looking at the four tube sockets make sure you have one tube in one of the two left sockets and one in one of the right two to keep the push-pull circuit balanced. Whether this will work or not depends on whether the other tubes were damaged when the known bad tube was blown. It will probably be your safest bet to remove both tubes from the side that the blown tube was on and move one tube from the other side over as those tubes were less likely to be damaged. If you don't know which of the four tubes is bad and don't have a spare set, get out those spare fuses you always keep with you. This can be tricky. It's possible that replacing the fuse will bring the amp back to life,but the question is for how long. Power tubes are notorious for shorting and then temporarily fixing themselves. You may get through your gig or it may blow in the next song. If the fuse blows right away you can try removing one output tube at a time with a new fuse installed each time to get the amp to come on without the fuse blowing. You have now found your bad tube and can proceed as outlined above to move tubes around to balance the push-pull output stage. One last thing regarding using your amp with two outputs instead of four. There are a lot of "gurus" on the Internet that say this can't be done because it will overload the remaining tubes and cause them to blow up. Each tube is its own amplifying device and doesn't know whether the other tubes are there or not so don't be afraid to try this.

SOUND IS COMING OUT BUT IT DOESN'T SOUND RIGHT

Sometimes we encounter a situation where the amp is producing sound but it is not right or behaving intermittently. First analyze what you hear. Is it not loud enough or distorted when it shouldn't be etc? With this in mind take a look at your controls and see if something is set wrong and causing this condition. If all looks right the next thing I would try is the first thing my grandfather ( a TV repairman) taught me. Strike the cabinet of the amp with your fist in multiple places. Does this cause or eliminate the problem or create crackling? If it does we are down to two possibilities. First there is an intermittent connection inside the amp. There is not much you can do about this and it is time to send the amp in for servicing. The other possibility is an intermittent tube. I would gravitate here to the preamp tubes. The output tubes can cause this but are more likely to short and blow fuses. EL84 output tubes are the exception to this. They are very likely to crackle, hum squeal etc. But The preamp tubes are the biggest suspect here. You can try removing any covers over the tubes and flick your finger repeatedly against each tube one at a time. If you can get a tube to cause the problem you are hearing, try replacing it with the spare preamp tube you always carry with you. If the new preamp tube does the same thing you may have a dirty socket. You can try inserting the tube in the socket multiple times in the hope you will strip off enough of the corrosion to make a good connection.

A preamp tube can also fail in a way that is not vibration sensitive. You can take your spare preamp tube and one at a time replace the preamp tubes in the amp to see if you can locate a bad one. Remember also, I find most of the time that any problem that takes a while to start, be it crackling, no sound, etc. is likely to be a preamp tube that fails when it heats to a certain temperature.

Another test method is to divide and conquer. You can try taking the preamp out or effects send to another power amp and see if you get sound. Same for another preamp into the power amp or effects return. You just might work something out to help get you through a gig.

ATTITUDE

I could go on and on with problems and remedies but I would like to touch on some things about attitudes and misconceptions people have that limit them from being able to solve even a simple problem when it comes up.

First and I hear these repeatedly,
"I just bought this, there can't be anything wrong with it". For those of you who believe this I invite you to my shop to see the pile of equipment to be fixed that has not even been sold to a customer yet. And my other favorite- "I've had this for fifteen years and there has never been a problem" I usually don't say anything to that- but I do give a long blank stare to the customer. Although if there is any truth to the above in a specific situation, these are the people who should be checking their wiring and control settings for problems since they believe there can't be anything wrong with their equipment. You may have used your amp 1000 times before, but that doesn't mean you couldn't of done something wrong this time or something was changed by accident.

Another attitude I see is the " artist" attitude. Those that believe their sole purpose in life is to create and can't be bothered or it is beneath them to understand anything about their equipment. I certainly respect artistry but if you are also performing in a professional or academic situation ignoring how your tools function can make you look like an amateur and robs you of the ability to create your art at the time if your equipment doesn't work. Take the time to learn your equipment. Read the owner manuals, ask questions to those who are knowledgeable about it. A better understanding of your tools will help your creativity.

Next month I will be talking about something close to my heart- How to get the best results when bringing your equipment to a service center for repair. It will be a great glimpse inside the customer service insanity I handle every day