Yamaha EMX 5000 -12 Powered Mixer - Cuts out and back in during performance

[zafatenapeach]

My Yamaha EMX 5000 -12 Powered Mixer was just worked on but did not fix the problem . A friend who also has the same board suggested to the tech to resolder the power cord to the circuit board , and did so with three small wires to supply flexibilty . Does anyone have any knowledge or ideas about how to overcome this problem ? It's such a great amp . Thanks .

[Jazz P Bass]

The first item on the list is to narrow down whether it is a power amp or a preamp problem.
Any competent tech will know of what I say.

[52 Bill]

Welcome to the place. What you haven't made clear, is how the amp is cutting out. Resoldering the ac input section indicates that the power goes out, meaning the entire board dies. Is this correct or is it just the sound that cuts out?

[zafatenapeach]

The first item on the list is to narrow down whether it is a power amp or a preamp problem.
Any competent tech will know of what I say.

Thanks Jazz P . I'll keep that in my notes . ave some other tests that I can do .

[zafatenapeach]

Hi Bill . Thanks for responding . The sound cuts out , but the lights stay on . I still ave to test further to determine if the levels change with the signal input . Most of my experience with thias problem has been on the job , with my back to the nit , facing the crowd .

[Brad1]

A friend who also has the same board suggested to the tech to resolder the power cord to the circuit board , and did so with three small wires to supply flexibilty .

I'd question the judgement of someone using smaller wires than what is used by the manufacturer for a power supply...or any circuit wire...if you are saying he did that.

The sound cuts out , but the lights stay on .

If that's the case, the power cord is not the problem. If the lights are on...it has power. The power is not getting to a circuit, or you have something connected/set improperly.

First thing is, take it apart and make sure all cables are properly and securely plugged in, where they belong. (WARNING! Make sure it's unplugged from the power outlet, and ALL capacitors have been discharged before touching anything on any board!! Large filter capacitors can store dangerous amounts of electricity, even after unit has been unplugged and sat for a period!!)

Next thing is...smell it. Does it smell of something burnt? If not, that may be a good sign. (And, you'd think the guy who "fixed it" would have noticed.) Look closely at all visible parts of anything you can see for signs of a burnt/cracked/exploded component, and look for a telltale "browning" discoloration of any area of any board that would indicate an component running extremely hot.

If that all looks good, carefully reassemble it.

With any cables unplugged (mic/insert/etc) except the power cord and speaker cables, and the proper impedance speakers connected, and the outputs set to "stereo"...with all the channel faders down, while raising the main volume fader(s) up, can you hear anything? Hiss...anything?

If no, pulling the main fader(s) back down, insert a pair of headphones. raise the mains, and if you don't hear much of anything, lower it to "optimal" setting and raise a channel fader. Do you hear anything? Play around with the levels. All you are looking for is some hiss.

If you hear anything, lower everything, plug something into a channel, and start raising levels on the channel and mains. Do you hear what you are playing?

If yes, it means it's getting through the preamp section, to the headphones, but not to the amps. That may narrow it down.

If no, turn down all the faders, and plug a 1/4" guitar cable into the first channel "Insert" jack, but only to the first "click". That SHOULD turn that into a "Direct Out", but I'm not sure. I'd have to see a manual or schematic to know if the "ring" is send, or return. If the ring is send and the tip return, then this should work to test. Plug the other end into a guitar amp, or something similar...AFTER turning down all the volumes on the guitar amp. Turn on the guitar amp, and raise the volume slightly. Raise the channel fader slightly, and see if anything you are playing through it comes out the guitar amp. May have to see-saw back and forth to get reasonable level.

If nothing, then it's possible something in/before the preamp section is bad.

If yes, then the preamp section may be good, and it isn't getting to the power section.

Try to narrow down the section, first. Could help to try to find a schematic or service manual for it, and take voltage readings at indicated places. Anyway, try all that and report back with any findings.

Good luck,

Brad1

[mozwell]

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[zafatenapeach]

Welcome to the place. What you haven't made clear, is how the amp is cutting out. Resoldering the ac input section indicates that the power goes out, meaning the entire board dies. Is this correct or is it just the sound that cuts out?

Bill , the sound cuts out but the lights remain on , and the level meter works . Thanks , Mark

[zafatenapeach]

It worked fine the other night , mysterious .

[QUOTE=Brad1;276643]I'd question the judgement of someone using smaller wires than what is used by the manufacturer for a power supply...or any circuit wire...if you are saying he did that.

* The three small wires were added to relieve streass internally to the circuit board . *

*The crazy thing is that I used the board saturday and it worked fine , with no problem . Could it be speaker cables ? * Thanks , Mark

[g1]

Yes it could be speaker cables. It could also be a switching jack problem, see this post: http://music-electronics-forum.com/t28549/
In your case the power amp in jacks are switching jacks. When nothing is plugged in to them, they route the signal from the mixer to the power amp. If they get dirty/oxidized, you may get intermittent cutting in and out.