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Author Topic: Most interesting troubleshooting?  (Read 1791 times)

Jonathan Johnson

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Most interesting troubleshooting?
« on: March 17, 2017, 01:51:01 pm »

What are some of the most interesting problems that you've solved in the audio world? I'm especially interested in problems that may have plagued systems for years, unique situations that required unique solutions (safe solutions, of course), or problems that were particularly difficult to resolve.

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As for myself, one of the churches in my denomination had a feed from the sanctuary system to the fellowship hall. They complained for years that the feed was distorted, and supposedly had several "experts" (possibly just music store salesmen) look at it without resolution. Since it's across the country from where I live, it wasn't something that I could just pop over and take a look at.

Back in 2000, that congregation hosted the national convention of our denomination and I attended. When I first walked into the fellowship hall during a service, my first impression was that it sounded like clipping -- most likely from an overdriven input. After the service, I took a look at how things were set up, and found that the feed was connected to a microphone input on the fellowship hall system, from a 1/4" speaker level output off the amplifier in the sanctuary.

It was a simple matter to move the feed from the speaker output to an available 1/4" line level output, and the problem was solved.

The moral of the story? Not all 1/4" outputs are the same. Apparently some "experts" haven't realized this.
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Lee Buckalew

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Re: Most interesting troubleshooting?
« Reply #1 on: March 17, 2017, 02:06:58 pm »

What are some of the most interesting problems that you've solved in the audio world? I'm especially interested in problems that may have plagued systems for years, unique situations that required unique solutions (safe solutions, of course), or problems that were particularly difficult to resolve.

----------

As for myself, one of the churches in my denomination had a feed from the sanctuary system to the fellowship hall. They complained for years that the feed was distorted, and supposedly had several "experts" (possibly just music store salesmen) look at it without resolution. Since it's across the country from where I live, it wasn't something that I could just pop over and take a look at.

Back in 2000, that congregation hosted the national convention of our denomination and I attended. When I first walked into the fellowship hall during a service, my first impression was that it sounded like clipping -- most likely from an overdriven input. After the service, I took a look at how things were set up, and found that the feed was connected to a microphone input on the fellowship hall system, from a 1/4" speaker level output off the amplifier in the sanctuary.

It was a simple matter to move the feed from the speaker output to an available 1/4" line level output, and the problem was solved.

The moral of the story? Not all 1/4" outputs are the same. Apparently some "experts" haven't realized this.

With students when I talk about connector vs. signal types, etc. I use the phrase "just because it fits doesn't mean that you should stick it in there".  :-)


Lee
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lindsay Dean

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Re: Most interesting troubleshooting?
« Reply #2 on: March 17, 2017, 04:00:02 pm »

Back in the analog 90s, I had been asked to run a local bands system for an upcoming show
    went to their practice room to see what they had .     after enduring about 9 seconds of the "monitor system" they had set up I stopped and asked if I could have a look at their rack.
  Fun stuff , eq out to speaker outs to  the next amps daisy chained 1/4 inch one to the other. I asked who hooked this up, the guitar proudly claimed the patching master piece.
 he says he just kept hooking up cords till sound came out ..............uh ,,,,ok   
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Scott Helmke

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Re: Most interesting troubleshooting?
« Reply #3 on: March 17, 2017, 05:09:58 pm »

Wow, most interesting?  I get a lot of repair calls for offices, churches, museums, run into all sorts of crazy problems.  Not sure I could even cut the list to a top ten.

Yesterday I was in a really nice museum in the city, their music room had the usual 9' Steinway piano but the sound system was a mess. 

The rack had a nice enough Qu-16, but all the mic inputs (from floor pockets) were super noisy.  I found some idiot had disconnected as many grounds as possible before giving up, but in the process of resoldering the shields on all the mic lines coming into the mixer I discovered that the XLR's had been wired wrong to begin with - pin 1 and pin 2 swapped, every one of the dozen channels.
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Adam Kane

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Re: Most interesting troubleshooting?
« Reply #4 on: March 17, 2017, 05:25:26 pm »

What are some of the most interesting problems that you've solved in the audio world? I'm especially interested in problems that may have plagued systems for years, unique situations that required unique solutions (safe solutions, of course), or problems that were particularly difficult to resolve.

----------

As for myself, one of the churches in my denomination had a feed from the sanctuary system to the fellowship hall. They complained for years that the feed was distorted, and supposedly had several "experts" (possibly just music store salesmen) look at it without resolution. Since it's across the country from where I live, it wasn't something that I could just pop over and take a look at.

Back in 2000, that congregation hosted the national convention of our denomination and I attended. When I first walked into the fellowship hall during a service, my first impression was that it sounded like clipping -- most likely from an overdriven input. After the service, I took a look at how things were set up, and found that the feed was connected to a microphone input on the fellowship hall system, from a 1/4" speaker level output off the amplifier in the sanctuary.

It was a simple matter to move the feed from the speaker output to an available 1/4" line level output, and the problem was solved.

The moral of the story? Not all 1/4" outputs are the same. Apparently some "experts" haven't realized this.

Weirdest one to date:

There was a church in town that had installed their own PA (surprisingly well) and had been using it without problems for a few years. Out of nowhere, the PA would suddenly produce 3 REALLY LOUD bursts of buzz/hum out of pretty much every speaker. It would do this every 37 seconds without fail whenever the system was powered on. They tried to figure it out for a few weeks, then called me. I proceeded to perform all the standard troubleshooting stuff (lifting grounds, unplugging cables between components, etc) with no luck. As luck would have it, I left my meter back at the shop...otherwise I may have figured things out quicker.

I knew it had to be power related so I'm walking around the building (not huge...auditorium was only about 200 seats) trying to spot anything that looks like its been messed with recently. Building was small enough I could hear the hum through the subs no matter where I was.

After a couple of hours, I ended up in the basement (old building, by the way) and kept opening up doors and exploring. I wound up in a little storage closet under the FOH booth (only door I hadn't opened yet) and was about to walk out when I somehow noticed a DeWalt charger sitting on a shelf...and in turn noticed that when the lights flashed three times on top of the charger (indicating charge complete), the system hummed three times...every 37 seconds. Noticed the cobbled mess of romex going from the receptacle up to an old surface-mounted porcelain fixture. I unplugged the charger, no more humming. Plugged a lamp into the outlet: HUMMMMMMMMMMMMMMMMMMMMM!!!!!! until I turned it off.

I told them to get an electrician in there. They ended up calling someone I knew. He told me the recept was wired with the black wire where it should be, the bare wire on the neutral screws, and the white wire cut off. That circuit was somehow tied into/feeding the circuits that fed the FOH booth and he found lots of other stuff (reversed hot/neutral, missing ground, etc). It had always been wrong, but somehow never displayed a problem until someone plugged something into that recept in the storage closet (probably the first time in decades). I almost didn't go into that room...never would have found it.
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Ivan Beaver

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Re: Most interesting troubleshooting?
« Reply #5 on: March 17, 2017, 07:23:29 pm »

My most interesting one was back in the VHF wireless days in the 90's.

The Pastors mic would cut out when he went to stage left.

After a bit of not getting it to cut out, I wondered about the B3 organ on that side.

I took the back off and the oil tubes were still full.  It had never been oiled.

So I turned it on and the mic would cut out.

I oiled it and let it run a little while.

Then the mic didn't cut out anymore.

It was "squeeking" and causing RF  spikes which were interfering with the RF.

It's not often you need a little oil to fix a wireless problem
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Mike Sokol

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Re: Most interesting troubleshooting?
« Reply #6 on: March 20, 2017, 09:32:56 am »

I've posted this on AC Power & Grounding, but it's a good brain teaser for here:

Some 40 years ago I had seemingly random pop/buzz noise bursts on my PA in a bar that seemed to be more frequent after each dance song and when we took a break. That is, during a song we wouldn't hear it, but right after a song there would be a flurry of these pops and buzzes, sometimes every 10 seconds or so. The management had installed new electrical outlets across the back of the stage, so they assured me it couldn't be a power problem. However, I kept watching the bar for anything happening that corresponded with the noise burst. And it happened every time they rung up a sale on the cash register.

After much troubleshooting I found that all the outlet grounds on the stage were tied together along with the electrical outlet for the cash register. However, none of outlet EGC grounds were bonded to the service panel neutral. So they were all floating together without a place for the current to go. Any voltage put on the ground of one of the outlets would appear on the ground of ALL of the outlets since there was no bonding connection to act as a current sink.

When my band was done playing a song, and the patrons were done with a fast dance they all ran to the bar for a drink, and every time the cash register made a sale the old-school solenoid on the drawer put a voltage spike in the EGC outlet ground. That voltage spike went right in my PA system ground and produced a big pop and buzz noise. It appeared to be random, but the noise burst was tied to another non-random event.

My point is that documenting the period of a failure and observing seemingly non-related events can give you a clue as to its source. There are very few truly random events. Most of them are caused by something we haven't observed directly which confuses us. Consider that before Nicolaus Copernicus  stated “We revolve around the Sun like any other planet.” there were a lot of crazy calculations required to explain why the planets seemed to move in strange ways, sometimes appearing to go backwards. Early astronomers didn't understand the concept of the sun being the center of the solar system, with all the planets orbiting about it.

Troubleshooting problems is getting to be a lost art since it takes time and logic we often don't have. But it's time and brainpower well spent.

Robert Lofgren

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Re: Most interesting troubleshooting?
« Reply #7 on: March 20, 2017, 10:38:54 am »

I have one 'audio' related thing happening to many years ago that really baffeled me...

I bought a car alarm for my car and did the install by myself plus some friends 'helping'.

After the installation was finnished I started to test it and noticed after a while that one of the piezo horns were always sounding. If was quite faint, like a speaking level tone coming from it. I was first going to ignore it but it became annoying quite quickly.

Since the piezo cable was pulled behind and hidden under the chassis I cursed as I belived that the insulation on its wire had been scratched somewhere when feeding the cable inside the chassis and was causing a slight shortcut of the power.

I decided to cut the red wire as it was starting to get late and fix it the day after. After cutting the wire the piezo was still sounding and I thought that I must somehow mixed up the black and red wire and decided to cut the black wire as well.

The piezo was still sounding with both its wires cut! No electrical connection whatsoever...

After one or two hours later I decided to give up and hope that no one else became annoyed by the sound during the night. When I was about to take the keys I noticed that for some reason I had inadvertently turned down the panel lights so I turned them back up again and the piezo pitchshifted! I realized that when the panel lights was fully lit the piezo was not sounding but as soon as I started to dim the lights the piezo started to sound.

I then realized that my car was not using a reostat for the panel lights but a pwm operated dimmer. For some reason the rfi leakage from that dimmer was enough to operate the piezo from a distance.

This has been one of my weirdest 'audio' related issue ever.
« Last Edit: March 20, 2017, 10:42:30 am by Robert Lofgren »
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Steve Litscher

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Re: Most interesting troubleshooting?
« Reply #8 on: March 20, 2017, 12:11:26 pm »

Just ran into an interesting situation on Friday, while providing a very basic PA and extremely small light rig for a small corporate party. About 100 people mingling in a training room on the 4th floor of a newish building. Only one circuit for the front of the training room, which is where they wanted the PA gear and lights.

Got everything set-up, tested the wireless mics, and got ourselves situated in an out of the way location. iPad in hand, all set to go, when all of a sudden there's the loudest 60Hz ground loop hum I've heard in quite some time. Runs for about 10 seconds, then stops.

I run up to the front, and check on the connections. While I'm checking, the noise starts again. I have my X32R on a UPS, so I unplugged the UPS from the wall - noise is still there. The powered speakers are also plugged into the same circuit (duh).

So, I put ground lift plugs in place, and there's no noise. Until about 3-4 minutes later when that same 10-second hum appears again. I'm starting to sweat because the event starts in 10 minutes. I'm trying to find a solution when the organizer/host comes up to me with a cup of coffee in hand, asking if we are ready to go.

I explain the phantom noise, and as I'm doing so, the noise appears again. In comes another person with a cup of coffee. It dawns on me... so I ask, "Do you guys have a coffee vending machine here?"

The guy says, "Yep - you need a coffee? It's right outside."

I walk outside, and there's a small coffee/latte/espresso vending machine on a counter. I order up a coffee and press "start" - and there's my buzzing noise.

We unplugged the coffee machine and put a "temporarily out of order" sign on it. The event went perfectly, and when we were done, the machine was reinstated.

Steve M Smith

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Re: Most interesting troubleshooting?
« Reply #9 on: March 20, 2017, 12:20:24 pm »

Not audio related:

Many years ago, my father was a central heating system designer (back in the days when every piece of equipment, pipe, fitting etc. was put on a drawing).

A system was fitted in a house and a few days later, the owner complained about a noise.  A fitter was sent out several times but could find no fault.

After another call, my father sent someone out instructed sit in the kitchen drinking tea until he heard the noise.

After a while, sure enough, there was the offending noise.  The house owner said "that's it - did you hear it?".  To which the reply was "yes madam - that's your fridge!".


Steve.
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