Behringer Eurodesk MX3282

[ENB]

I was prepping my PA system this evening and lost about half the gain on the left main of the board. While I am not certain, I believe it dropped about the moment, I was trying to roll in a little more Aux2 (reverb unit) at the Aux 3 master.

First appeared as the Bottom two speakers on one side sounded weak could practically only hear the horn. We isolated speakers to rule them out, bypassed FX unit, EQ unit and swapped things around to rule out the Main Crown amp, it was ok. It came back to the Left Main output of the board simply lost about half it's gain.

We rechecked the pan pots, assign switches, etc all ok. In ever other aspect this board is working properly. We compensated with about double the fader on the left ch (still below unity) and the channel sounds simply wonderful.

Any advice on further isoloate this? I have read ENZO's other post on isolation but I assuming there is a preamp section that pre amps that left channel as it leaves the board (not sure). This board uses an external power supply, would the op amps etc be in that ext. power supply?

Any ideas or should I just run it as it is?

Thanks,

ENB

[Jazz P Bass]

MX3282

The opamps are inside the mixer.
Every channel, from left to right, is a duplicate.
Over on the right, at the mains faders, is where everything comes together.
If you feel like stripping it down get a bowl for all the screws.
It sounds like it could be:
a bad cap
a dirty slider
a bad opamp
crappy soldering

[Enzo]

If you have done this, then the mixer has the problem:
Set up the board so the same thing should come out L and R. Center the pans, max the subs or don;t use the subs. etc. In fact, better at first if you do not use subs - assign the test signal channel direct to L/R main.

Now run a cord to the input of one side of your amp and connect a speaker to its output. Apply a signal to an input channel on the mixer and run it up.

Plug the cord to the amp into L OUT, then R OUT. Back and forth. They sound the same or they don;t. We are doing that instead of connecting L and R to two channels and two speakers so the two mixer outs are feeding the eexact same thing for test.

If they sound alike, they are not the problem.

Do the VU meters show a difference or not?

Assuming they are different -
You have a sea of patch jacks. The main L/R out are XLR, but are there not some 1/4" main L/R out jacks? Try them. Are there not some main L/R insert jacks? Try those both ways - - use them as an output to some other amp for a listen, same or not - and use them as an input. Both work same or not.

In fact, squirt some cleaner down the insert for the bad output, and probe a plug in and out a few times. ANy help?

Try the main slider at half up and at full up. Does it even out at full?

How about in the headphones? Even or not?

Bottom off the board, flip it over with enough hanging off the table you can still conect to it. Find the pins of the main L/R fader - scope them. No scope? APply a strong signal at an input channel and follow it with an AC voltmeter. You should be able to determine which pins on the fader are input, ground, and wiper. Are the input pins showing the same signal or not? And the wipers?

[chipprogr]

I am new to the forums but look forward to sticking around and helping out.


IF you have not yet compaired the left and right main outputs by switching your cables back and forth to verify that it truely IS the console and not a bad cable, then do it 1st before continuing with anything else.


Your description sounds exactly like you lost either the positive drive (pin 2 or tip) or your negative drive (pin3 or ring of 1/4"). This can cause a 6 db drop in signal and sound exactly as described.

You can trouble shoot this with a set of headphones. Hook up your headphones as normal. We are going to use the console as its own diagnostic tool.

1st- lets use channel ..umm..15 for example. solo it so your only hearing the "INPUT" to channel 15. KEEP THE FADER DOWN ALWAYS -ONLY SOLO THIS CHANNEL. THis will be our listening probe

2nd- grab a cd player, mp3 or some other music device and plug into some other channel, set EQ flat, route to L/R main output. bring music channel up to unity, bring main fader up to unity. Are the meters showing the same??

3rd- Yes there are opamps that setup the drive for output, no they are not in the external power supply. The main outputs of this console are balanced, meaning that it has a positive drive and negative drive at the jacks. Plug a 1/4" cable from chan 15 input to the left 1/4" output. Start by plugging it in only 1/2 way and listen, if all sounds good then plug it in all the way. still sound good? Now repeat for the right channel. This way we can isolate the positive and negative drive opamps. Compaire back and forth. then grab a mic cable and repeat using the mic xlr input(chan15 ) and the xlr main outs. Listen to them both.

Last , if you DO find a drop in either of the outputs, use the 1/4" cable to listen to the Main Insert Jacks. if all sounds good here but not at the main outputs, then your final drive opamp for that output is bad. It will probably be a njm4580 sip type. If it sounds low still at the insert points, but your main meters read the same, your problem is post main fader, but pre insert point. There should be another opamp driving the inserts.

Hope this gets you started to finding your proble. Keep us informed of what you find


Thanks-eric

[ENB]

Thanks for the great advise.

Eric, I have just now had a chance to get the board back out as I had replaced it with an alternate 16Ch board I had. Finally I have had time and oppertunity to set the board up again and tweak with it. I plan to walk through the steps you and Enzo recommend this weekend, only problem is I hooked it up yesterday and the output on both main busses (L&R) were working fine. I have twice had this thing lay down on one side at sound check. I know an intermident problem can be hard to ferret out.

In light of the intermiddent nature of the problem, I am starting to suspect one of the faders on the affected main buss. I hope to reproduce the problem when I have the system set up at home giving me a chance to cleck it out when it's doing the deed. I can always run Mono but I like for things to work as intended.

I will report back if actually find the source of the problem.

Thanks for all the input thus far.

[ENB]

I was never able to locate the source of the intermiddent issues with this board. After I could not replicate the failiure at home, I put it back on the road and have used it for the past year. A while back, it repeated a profound drop in gain on one of the main channels. Not really wanting to switch to Mono, I thought perhaps a cold solder joint so I gave the board a whack with the heel of my hand on the corner of the board near the main faders and the channel re-acerted itself and we played several more gigs without issue. Last night we used and developed a crackling that appeared to be in one of the main speaker horns. All Gains checked clean so I wound up puling that down and panning some channels away from that output. Left. Later in the night I switch my speaker cables and the problem followed the main output speaker cable (which checks good). The only thing I got from the last speaker was only the AUX Reverb wet signal with none of the more powerful left main signal. Whacking the board again did not help at this point. Rather than a component failure, am I correct that this narrows the problem down to either cold solder joint on the main output channel or less likely, a pin in the external power supply that is loosing contact. Also, I power my main AMP with the XLR outputs from this board. My piano player plugs in to the left 1/4" main output to send a signal to his powered personal monitor. Could doing that over tax the op amps for that channel? Everything is pointing to the main left signal path at this point after having gone through the flow chart Enzo gave me good while back. I will not send the board off for repair due to it's cheap price tag when new however, if I dont find a Visual problem, I don't think I would ever trust it to gig with again but I just hate to chunk it.

[ENB]

I now have the board powered up and running, upside down where I can access Channel one and the sub and master fader section. Since the hand bump this morning, all is well. I probed every conceivable solder joint associated with the main signal flow. I have not yet tried introducing hot and cold to the board yet but not sure how much time/dolars I am willing to invest in this board. May be time to chunk it but I would be afraid to buy another Behringer product after this gremlin.

[g1]

Have you checked the main insert jacks? If not, please see the sticky post regarding switching jacks in the maintenance section of the forum.

[twitch559]

i had the same problem on my beheringer eurodesk sx2442fx, i was setting up for a gig and all left mains went deft so there are 2 simple salutions that i use because i run 2 boards,
#1 send the mains threw a subgroup,
#2 run a line from the right output to your right speaker set, then bridge your left speaker to the rights