Phantom Power issues maybe?

[JMackenzie]

Hi Guys and Girls,

I am new to this particular forum, and so so glad I have found it.

At long last I know that someone out there will have the answer to my problem.??

 

I use a Behringer SL3242FX-Pro mixing desk at work, which is a permanent fixture, never been moved, or seen the light of day since its installation in my school theatre about 3 years ago.

Last week it started behaving badly, power switching off and on evey 3-4 secs, after 5 mins from powering it up.

I removed all outputs, and inputs from the desk and observed its behaviour over a period of time. To cut a very long story short, and finding no help whatsoever from Behringer or their one and only service agents in this country, I have resorted to trying to fix this thing myself.

A Few facts which I notice , but cant get my head around , but maybe you guys can .

 

If I switch the mixer on , without the phantom power on, it stays on for hours.

If I then put the phantom power on , after 5 mins the whole thing starts this on / off cycle.

 

I realise that the power supply is faulty, but I am told that THEY ( Service centre for Behringer) cant source one because of Chinese suppliers being unable to provide the item within a sensible timescale.

 

My question to you guys is however a bit more searching .

In normal use , I would be using 5 Sennhieser radio mics(lapel type), a couple of hand held AKG radio mics , some SM58's , and a few CS1000 condensers, and DVD or CD inputs to the desk.

The desk has global phantom power, so has to be on for the condensers.

Could I have damaged the desks power supply by trying to feed all these different inputs with the 48Volts.? :)

I am normally very careful about what gets plugged in to the inputs, but unfortunately I am not the only person to use this desk. I know that one of the teachers in the school ran a DJ rig through it, and I know that he used the XLR mic inputs, for his line level output from his onstage gadgets, even when I had asked him to use the line inputs.

Something has caused this problem. :)

I would really welcome any suggestions about using all these multiple inputs to the desk, whether or not they are compatible with global phantom power.

I was so impressed with the quality of dicussion on this forum, I just had to join.

I have knowledge and abilities in all aspects of theatre and music, and instrument repair.

I hope I can help one of you people one day. :D

[KevinE]

The power supply isnt seperate on this is it? Its a built-in switchmode supply.

 

You can mix and match inputs with/without phantom, it's how they all work, this wont overload the desk. If putting the phantom power switch on trips the supply then it's faulty. If you're not competent to fault-find at component level on this, the only option is to book it into a repair shop.

 

EMS who are the Behringer repair centre are unfortunately at the other end of the country (Southend on Sea) though I'm sure it doesnt take a main dealer to fix it!

[cedd]

If repair isn't an option, now may be the time to invest in a few cheap external phantom PSU's. On the up side it means only the mics you want to receive phantom actually get it.

Then just deactivate the phantom switch and pretend the desk never had it.

[Rob_Beech]

Maybe it's a way of getting you to not use the C1000's :) I'd take it as a blessing.

 

On a more serious note, clearly if nothing is plugged in and phantom is switched on and it fails it needs a repair. I'd try and source a local place first. There is no warranty on this so you are not tied to the main dealer.

 

Now may be time to invest in a new desk, or pre's with phantom as mentioned above.

[StevieR]

While not trying to disrespect behringer equipment, we need to remember that this is a budget brand and does not have the reliability of more expensive desks. Its been in place for three years now and has developed a fault out with its warranty. If it was me I wouldn't waste time trying to repair the thing just go out and buy a replacement.

 

Steve

[Rob_Beech]

To add to Stevie's post. Remember, buy from the right place and you'll get a 3 year warranty. If you can put up with them maybe not being the nicest pre's nicest eq's and being a little noisy at best then they're worth their money for 3 years use, anything on top is a bonus.

[johndenim]

Maybe it's a way of getting you to not use the C1000's :) I'd take it as a blessing.

 

I was wondering how long it would take Rob... :D

Ageed, agreed, agreed.

It does sound like a earth fault loop impedance fault?

Well certainly a fault on the PSU.

 

At beginners level electronics you would be wise to get this looked at properly.

 

In the meantime what's the chance of using some dynamics instead?

After all you can't do much worse than a c1000. :)

[david.elsbury]

John, what do you base this statement on:?

It does sound like a earth fault loop impedance fault?

[dvidos]

I have seen such behaviour in other electronics equipment too. I am no expert, but my best guess is that, somewhere inside or near the PSU, there is an electrolytic capacitor (or more than one) going bad.

 

You will see it expanded or leaking some dark fluid. See if you can change that with a new one.

 

Dimitris.

[MarkPAman]

The OP said CS1000 rather than C1000, but if they are C1000 they can run on batteries. As these appear to be the only thing that needs phantom it's an easy work-around for the moment. (Sorry Rob :) )

 

There's all sorts of things that could be causing this, it's not necessarily the power supply that's faulty. Find a good service engineer, it probably won't cost that much to fix.

[JMackenzie]

Thanks to everyone for your opinions.

You are all reinforcing my own thoughts on the matter.

 

Johndenim----I am curious about your comment on earth loop fault. I DO certainly have earth loop issues in this theatre. I have to run all my audio gear from the same outlet or I get the most awful hum. One thing that does happen however, if I unplug the ac inlet cable to the mixer, there is a very loud hum produced by the system. I have never quite understood this. :)

 

Kevin----- I have contacted EMS and had a good chat with them, just two days ago.

They were going to find out if they could source a power supply and get back to me. They have not contacted me yet. PROLINEAUDIO is meant to be the only authorised service centre for Behringer. They were the ones who told me the power supply was bad, they have come across this before, but they also said the could not help because they cant source the part, and repairs they have made to others have also failed in a short space of time.

 

Cedd---------I can run the condenser mics on batteries, and I do have an external phantom power (Audiobuddy). My concern is more that I may have caused the damage to the pSU by something done in the past. I feel I cant trust this PSU even with the phantom power switched off. The School show happens real soon, and is quite a big event. I am tempted to hire a desk for the event, but for two weeks of rehearsals, 3 nights of show-----it would be a bit expensive.?

Rob------I would love a new desk. I would go for an Allen@Heath PA20 if I could find the money. Would you people think that would be a good choice?

The Behringer has been perfectly Ok for my purposes until now. I do think that it has become more noisy recently--more a hiss than a hum, which I never noticed at all when I first installed it.

 

I was wondering if another manufactures PSU would be compatible with this board.

I do hear tales of "extreme similarity :) " of Behringer gear and other brands.

 

thanks again for your help.

John

[KevinE]

I doubt it John. Behringer design and build all their own stuff in their own factories. The PSU will be a custom board that occupies a corner of the chassis, with multiple rails for the various sections of the mixer connected by a ribbon cable or two.

 

As you've already suggested, this symptom may be the tip of the iceberg and a forewarning of a further (maybe complete) failure of the desk, usually at the most inconvenient moment.

 

I'd definitely take it in, any decent service engineer should be able to track down a fault as simple as you've described if they're worth their oats.

[sleah]

This may sound a long shot, but something has just crossed my mind after the earth hum comments....

 

Using separate outlets, even separate phases shouldn't cause the symptoms as you describe, not as bad anyway.

 

Could there be a major earth fault in the building? :o

If there were a bad or no earth to the Beheringer, there could be all manor of bizzare 'faults', maybe including phantom.

 

Many years ago I had a mixer that gave constant grief in one particular drama hall, but was fine every where else, it subsequently turned out there was an earth problem with the circuit in that room

 

The Beheringer may of course be class2, but even so, it only needs one piece of class1 kit with a poor earth...... :unsure:

 

Long shot I know, but worth considering. Could you try the system in another building? And/or get the mains tested?

[JMackenzie]

Hi again guys.

Yesterday I decided to have a good tidyup of all my power outlets which were scattered around tables beside the mixing desk and the lighting desk. The power outlets are all , as I said, running from the one 13A socket, but at the end of a 30M cable, because ,in someones wisdom, the power outlets I had beside the mixer station were removed when our Rector got given a new office through the adjacent wall. I suspect the earthing is not good. The guy who installed our PA system actually tested it and found a difference in "potential ", as he described it between different outlets in the hall. I dont understand what a difference in Earth "Potential "means. I am going to get a proper electrician in to get the whole thing checked out .

 

However, to our tale, as the saying goes---------.After this big tidyup, I removed the back cover of the desk, to see how easy it will be to change the power supply, if and when I get one. That looks very simple, just one ribbon cable and a few screws.

I put the cover back on and switched it on . No problem. Swithed on the phantom power, again no problem. left it on all day with a CD player pumping it up to nearly max. output. No problem.

Next day, I plugged in all my Radio mics. turned everything up pretty high, with the PA amps down at minimum. No problem running it all day like that. !!!!!!! god I hate this kind of fault. In some ways I wish it had just packed in altogether to force the issue of replacement or repair.

I do think that it is pretty noisy, and when up at max on faders etc, there is a loud 50 cycle hum as well as hiss.

I have removed it again, and at the moment it is sitting on my workbench in a completely different area of the school. It has not displayed any kind of power problem now, for 2 whole days. it seems a little bit quieter on the noise front up in this room, but still noisier than my old Phonic 6 Channel one.

 

I can only hope that this fault comes back before any important event. I have other mixers which will do ,at a push , if I cant get this repaired. (even though it seems to have fixed itself) . Maybe I improved the earthing by shifting things around??

 

I will report back if it gets fixed or breaks down again.

 

Many thanks to all of you for your help.

I will start another topic on a new problem that has come to light. :unsure:

[sleah]

there is a loud 50 cycle hum as well as hiss.

 

Oh oh oh yeah that really does sound like a mains earthing issue, even Beheringer shouldn't exhibit noticable 50hz hum :unsure: , hiss? yes by the bucket load at full gain ;) :o

 

Stripping it down / moving it will have highly likely changed something in the earth department, especially if the fault is in the desk rather than the 13a supply like I suggested.

 

Although your previous sparkie has suggested a possible problem.

 

"Earth potential difference" is basically where there is a voltage difference between two earth points, say two 13a sockets at different locations.