Mixer Amp Burned Out?

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Mixer Amp Burned Out?

Postby Brotuulaan » February 15th, 2016, 2:18 pm

At our church, we got a used Peavey XR 600C for use in our fellowship hall for music and movies and such. Last Wednesday night, the sound apparently was "bad." I wasn't in there to listen to it, but we had a movie night last night, so I got to see what it was like. Here are the symptoms:

-Distortion with loud signals, occasionally with quieter signals
-Random volume changes
-Tone dropping to very mellow in short spurts

It IS used, and we never expected it to be a permanent solution, but we only got it recently, so we're hoping to still get some use out of it for a while. But we obviously can't use it if this is the new norm. Does anyone know what the particular issue may be?

We haven't had any storms recently, as far as power spikes go I've found it turned on after several days on several occasions, but nothing was running through it, so I don't know how much the standby power level/dust/heat buildup may have contributed to the current condition.

Any help you might be able give is greatly appreciated! Thanks!
-Brotuulaan

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Re: Mixer Amp Burned Out?

Postby Farview » February 15th, 2016, 9:03 pm

That really sounds like a switching jack is dirty. Are there any inserts on the channels you are using? The insert jack could be the problem.
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » February 16th, 2016, 11:04 am

Nope, no inserts. I forgot to also mention that it happened both on the tape in and in a channel strip, just the same in both.

Good thought though!
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Re: Mixer Amp Burned Out?

Postby MASSIVE Mastering » February 16th, 2016, 8:34 pm

Sounds like a job for Deoxit... At least at first...
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Re: Mixer Amp Burned Out?

Postby Farview » February 17th, 2016, 1:26 am

Yup. It still sounds like a bad connection, dirty pot, etc... If it is happening on multiple inputs, that means the problem is in the master section.

I just looked at the manual. The graphic input is a switching jack. That will be your problem. Get a 1/4 cable and plug it in and out rapidly a few times and see if it clears the problem up for a while. If it does, you might need to open it up and clean the jack.
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » February 17th, 2016, 2:46 pm

I looked through the manual when originally posting this, but I hadn't thought of that in connection with your original comment. Thanks for the idea! I'll try this out and let you know how it goes!

Massive, I'm guessing you mean the same thing as Farview? Or are you thinking the main outs?
-Brotuulaan

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Re: Mixer Amp Burned Out?

Postby MASSIVE Mastering » February 17th, 2016, 3:25 pm

More or less --
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » March 2nd, 2016, 1:00 pm

Haven't replied like I should have. Sorry this is coming so long afterwards.

I tried working the switching jacks like you had suggested, but no change. We have an old mixer that I pull out for a sound class we're running on Wednesdays, so I'll try using that to bypass the on-board mixer, then I'll try bypassing the on-board power amps and send the signal to a powered speaker. I'll let you know how those steps go. If you have any other suggestions in the meantime, they're more than welcome!
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » March 3rd, 2016, 2:58 pm

I'm back at the troubleshooting today, and I wanted to ask you guys another question.

What does a burned-out amplifier sound like? I've heard plenty of blown speakers before to recognize the farting noise they make, but I've never encountered a failed amplifier.
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » March 3rd, 2016, 3:11 pm

I was just looking online for references to power amps failing, and one of the things I came across said that if a capacitor fails, it often presents itself in the form of "motorboating," or when there is a "continued popping or putting sound."

Do you guys know whether at is actually constant or if it is actually dependent on the signal coming through? If it is constant, then it isn't as likely, but if it is dependent on the signal strength and makeup, then maybe this could be it. At this point in time, the sound coming out kind of pulsates with the level, with quick, distorted peaks and returns to low volume levels. As I turned it up earlier, it spiked very loud and was super-distorted.
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Re: Mixer Amp Burned Out?

Postby Farview » March 3rd, 2016, 8:05 pm

Take a guitar cable and plug the main output into the power amp input on the front panel. If that solves the problem, it is the switching jack.

Motorboating is a constant putt, putt, putt sound. All the things that you found describing the sound of a blown mp are constant sounds. If that is happening, you will not hear any of the signal you are running into it.
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » March 7th, 2016, 2:13 pm

Hadn't thought of that option! Thanks, Farview! I'll give it a try and post the result.

And that's good to know. Now I'll have a better idea for the next time I run into something like this!
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Re: Mixer Amp Burned Out?

Postby Farview » March 7th, 2016, 5:21 pm

You can avoid the switching jack while still using the eq by coming out of the main output, into the eq input, out of the eq output and into the power amp input.
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Re: Mixer Amp Burned Out?

Postby Brotuulaan » March 21st, 2016, 3:34 pm

Tried it straight from main out to power amp in, but I couldn't really troubleshoot just then because I was having an issue with one of the speakers. I stepped on the cable going in, and it damaged the input. I think the leads going to the low and mid speakers are damaged, because the tweeter was the only one going consistently, while the other speaker was performing normally.

I'll have to take it in to the shop and have them check it out before moving forward on it. I'll update here once I get that taken care of.
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