No Trouble Found

[drewl]

What do you do when you can't duplicate the customers problem.

It's like people that take their car in for repair and it works fine for the mechanic. Not me I do most of that stuff myself.

A Carvin X100B head, dude said volume dropped like in half, did it twice with all different outboard gear.
A national touring band with a special gig tomorrow.

Tore the whole amp apart and couldn't get it to crap out.
Presence pot was broken, but didn't effect output.

Output tubes do have about 300 gigs on them, so im replacing those to be on the safe side.

[The Dude]

Often times when this happens, I find that the problem is a piece of the puzzle I don't have in the shop. Bad guitar cord, intermittent speaker cord or cabinet wiring, something in front of the amp like a pedal or wireless unit. When this happens to me, I'm just honest with the customer and tell them I couldn't find anything. I offer to look at the "system" as a whole if they want to bring in the rest. If they're not interested in that, I give them a few troubleshooting tips to try like maybe try some different cables. Plug the guitar straight into the amp bypassing any processing, etc.

[Tom Phillips]

I have had two of these situations just recently. Both amps were reported to have intermittent signal drop outs. Both owners swore that they had eliminated all their other equipment as a source of the trouble. I found nothing wrong with either amp. Upon detailed questioning each owner separately admitted that they had never tried a different guitar AND a different guitar cord AND without their pedal board in the signal chain and had the amp malfunction. After I returned the amps they never reported a recurrence of the problem in the months that have gone by.

One guy said that he figured it was not a pedal board problem because he hooked that pedal board to another amp and it "didn't cut out" during that test. It took some patient explaining for him to understand why that brief test was not a definitive diagnostic for an infrequent intermittent problem. I think he had at least five pedals. With all the patch cords, that presents a lot of opportunity for a connection problem. Anyway, I had worked on the amps within the last year so I guess the mindset is to suspect the thing I worked on.

As to how I deal with these problems. It all depends on the situation. Ideally, I ask the owner to demonstrate the problem when they drop the amp off for service. If they cannot show me the malfunction then you are half way done.

[The Dude]

When the customer says THEY checked the rest of the system, it means little to me. There are some players out there who have trouble making change, let alone getting through some minor troubleshooting. I had a guy call a few months back who said "His effects didn't work through his amp". I asked if he was using the effects in front of the amp or in the effects loop. He said, "I don't use a looper". After much "back and forthing" and a questionnaire about where cables are plugged in, I never did get to the bottom of his setup. I'm pretty sure he couldn't either. He brought in the amp only............no effects unit or cables with it. Of course, it worked fine.

[Enzo]

MAybe 15% of amps come in with nothing really wrong, other than maybe some maintenance.

But if I believe the guy, then I invite him to bring his whole rig in and set it up in my warehouse, and to demo his problem.

But let's assume it really is in th amp, but you can't make it happen. Or maybe it did it for you once for three seconds and never again. SO we check the usual stuff.

Whack the top with your fist, any reaction?

You can check voltages, but really, off voltages don't generally cause sound dropouts. You can check the solder under every jack and control. If has tubes, check or redo the solder on the sockets as well. Loose socket pin? Wiggle each tube and see. Rap on the ends and open edges of the chassis with a rubber mallet or the handle end of a large screwdriver - anything to send a jolt through it. ANy reaction? Use something insulated and push down on the circuit board every inch or so looking for any reaction to the flexing. While signal is playing, move each and every wire.

This common repair request just screams "loop jacks" to me. You can "check" the jacks, but the thing to do is measure the resistanc across the cutout contacts. If there is a low resistance like 2 ohms or something, the amp will still work, but the fact it is 2 ohms instead of zero ohms or under 2/10 ohm tells me the contacts are dirty and vibration or thermal expansion can easily cause them to lose good contact now and then. Any contact that measures under half an ohm is probably OK, anything over that needs service, even if it is working right now. But check EVERY jack. Remember, headphones jacks can cut out speakers. Even a footswitch jack can cause trouble. Someone might always use the lead channel, and a weak jack lets the amp switch to the clean channel by itself and if the controls are down - lost sound.

Try flexing aany plug, like speakers, side to side in its jack. I had a run of Fender amps with speaker jacks that caused low sound. There was enough room in the speaker jack that if the plug leaned to one side, it aallowed the shorting contact to touch the tip blade.

[MarkusBass]

In similar cases I tend to believe the customer. I had at least two cases when the problem occurred once per month, or even less frequently.
In the first case it was really something simple - old power cord broken inside just a little bit (in a 40 years old Fender).
In the second case it was something much more difficult to find. In fact there were at least three problems in the amp. I found out a loose Speakon connector, loose wires on the input of the power amp (symmetrical signal - one hot wire with poor contact) and loose wires between preamp and power amp (also symmetrical signal). I was very difficult to reproduce the problem by when I pressed the wires in a special way, volume of the amp has dropped twice.

Mark

[drewl]

I checked everything, whacked everywhere, wiggled everything you can think of.

And normally I don't believe players when they say they changed their guitar/cable/speaker but this guy I know.

I explained it to him, and he understands.
Your average weekend warrior I wouldn't be too concerned with, I care and want to make sure things are right but I don't want something crapping out when these guys are in the middle of the Warped Tour or playing in front of industry people.

Got a Wampler Plexi Drive with same thing.
Think the switch is sticking on that though.

[Justin Thomas]

I got this same complaint just once. Ran the amp (SR RI) hard for two hours, poked, prodded, everything that wouldn't require soldering. Gave it back and asked "where werenyou when it happened?" "A tiny dive that was kinda sketchy..." I figured the voltage and wiring was so crappy that it couldn't habdle what they were trying to run through it. He said the amp never did it except that one time in that one place, and that "tube amps just do funny things sometimes, huh?" I said if it does it again when you play there, that'll narrow it down. Blame the venue, that's MY philosophy!

Justin

[drewl]

I've had people know it was bad power from certain places that have caused problems.

I get like one repair a month due to bad power from a certain venue!

[Mick Bailey]

Often times when this happens, I find that the problem is a piece of the puzzle I don't have in the shop.

Like this runaround I had. Trace Elliott head blowing fuses. Every dual pot had a crack in the outer track, but that won't blow fuses. I fixed everything and put it on my test rig. Two hours as high as I dared run it with a sine wave. Numerous on/off cycles while monitoring current draw. Nothing. Back to the owner who took it to a wedding gig that same day. Blew right away. I asked if the cables were OK - he said they'd been used previously without any problem. His bandmate confirmed this. So I got the cables and to be 100% removed the output board to compare with the connector wiring.

It's impossible for this to have ever worked - its wired as a dead short. But the customer is ALWAYS right.

http://music-electronics-forum.com/i...attach/jpg.gif

[g1]

The cables had been used previously without any problem... in another amp!

[Randall]

Whenever my time is wasted on something like this, and the customer ends up being some stoner kid who knows nothing, it tends to put me in a generally bad mood indeed. My policy is I don't charge what I don't fix. But I also will send that guy to GC next time.

[drewl]

No, no, next time he gets a surcharge.

Well I did find some other issues that needed to be dealt with, like replacing the voltage filter caps and a noisy opamp, so he's getting the amp back sounding alot better than before.

[Enzo]

I usually believe the customer's complaint, but I usually do not believe his diagnosis.

[The Dude]

I usually believe the customer's complaint, but I usually do not believe his diagnosis.

Agreed, which also is often a problem- customers not recognizing the difference between a symptom and a diagnosis. In the "SYMPTOMS" box of my work orders, I'll often see things like "bad tube", or "short", etc. This is not helpful in the least. I want to know why you brought the thing in. WHY do you think a tube is bad? WHAT is causing you to think there is a short? Is the amp distorted, dead, other? We need to know what SYMPTOMS we are supposed to correct.