Behringer MX 3282A mixer, no output

[mfreqmaster]

This giant mixer has no output from anything as far as I can tell. When I power up, the lights blink like a Christmas tree. My guess would be the power supply but I don't know what voltages the pins should be. Any help would be greatly appreciated.

[Jazz P Bass]

Opamp voltage

Check the + - voltages of an 8 pin opamp, 4580 comes to mind. ( I do not have the schematic) Pin 4 is -15 volts. Pin 8 is +15 volts.

[Enzo]

If you find most any mixer with ALL the peak lights on steady and no output, it is a pretty safe bet you have lost one of your power rails. This board runs on +/-17v from the power supply. Chances are real good that the negative regulator is bad, though other things are possible of course.

You can run the power supply without the mixer loading it, but often the faulty regulator will work without the load and collapse under load.

Inside the power supply, the chassis is not common, so don;t bother connecting your meter to it.

SO inside the power supply, there is a Molex connector that the cable to the mixer plugs onto. I use it. Test points are marked on the circuit board too. it is connector X5
and has 7 pins. Pin functions and test points numbered on board:

1 - +17v TP X2
2 - -17v TP X1
3 - +48v TP X4
4 - common
6 - +5v TP X3

5 - +12v
7 - common for +12v

Those two commons are separate. You can;t measure the +12 with your meter grounded to pin 4 for example.

The +/-17 is for the audio circuits, the +5 is for logic, the +48 is phantom power of course, and I forget what the separate 12v was for, light sticks maybe?

My money is on a bad LM337 negative regulator.

[haydenjames]

I have the same problem...

I have a Behringer 3282a and when I plug it up to the power supply all -20 and peak lights come on and stay on. I've replaced the LM337 negative voltage regulator and I've replaced the LM317. When the board is not connected to the power supply all IC's run cool, when I plug the board in, all run cool except the LM317 (+17) ic. It gets so hot you can't touch it! Where do I start looking now??? The board itself, or should I just continue to replace parts in the power supply?

- HJ

[Enzo]

When all the lights come on, it means you are missing a 17v rail. Usually caused by a regulator failure. But a short within the mixer could also load it down.

I'd start by disconnecting sub sections and monitoring the supply ail.

COuld be anything loading it down, bad IC, bad tiny bypass cap at a chip.

[haydenjames]

Thank You For The Quick Reply Enzo!

I got it up and running! I really appreciate your help and posts Enzo! YOU ROCK! I pulled the board apart, cleaned it up, didn't do anything else, put it back together and it works like a dream! I kind of felt uncomfortable with it just starting to work after putting it back together but I took it to rehearsal tonight and we used it for 4+ hours and it was just fine! I'm excited because I bought it off craigslist for $150 with the power supply. Got it from a church and it looks and now WORKS like brand new! I only put in the 2 regulators which cost me 9 bucks all together! A $159 Behringer MX3282A = AWESOME!

- HJ

[jhelm_waterw]

Wow... the pin outs for the power supply !!!!
I just picked up an MX series for cheap with no power supply.
I know how to build them but didn't feel like ripping apart the desk to reverse engineer it.
Thanks ENZO !!!! You rule!

[jhelm_waterw]

Actually... let me ask one further favor/question....
What is the pinout on the 7 pin xlr style connector?
I'll probably end up having to change that connector anyway to something I can find (if I build the PS from parts)
THanks
JH

[jhelm_waterw]

Actually... let me ask one further favor/question....
What is the pinout on the 7 pin xlr style connector?
I'll probably end up having to change that connector anyway to something I can find (if I build the PS from parts)
THanks
JH

Wow... I thought the 7 pin xlr's were a completely rare custom beast. Not.
I found & bought some on ebay no problem. Ok. Sweet.
Now to determine the exact pinout.

[Enzo]

XLR-7, should be a commodity item. Glad you found them, I might have tried Mouser too.

I don't know the XLR pinout. Just use continuity checks from the connector to the mixer innards. The XLR is not on the schematics, only the boards are schematic'd.

[beatlejoos]

New to the forum. Just a great big thanks off the bat. I have the same mixer and it had same problem and you cured it Enzo. Now I have a working mixer back instead of an oversized paper weight that blinks at me. The best if the net is right here. Many,many thanks.


"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side."

[Pigyboy]

Hi,
I have to resurrect an old thread. I am having the same problem as mentioned above. I tried Enzos check of the voltages above in the power supply. Without the load the LM337 reads about -17 volts but it drops to zero under load while the other regulators still read close to their prescribed voltages. I replaced the 337 and am still getting the peak lights on all across the board. I did notice that the voltage reads properly under load for about 15 seconds then the lights come on and the voltage drops to zero. I only had one new 337 on hand or I would try another in there. What should I check next?

Thanks in advance for any help.

Cheers,
Chris

[Enzo]

Then perhaps the regulator is shutting down from excess current demand.

You can disconnect the wires and insert an ammeter to check current demand from each rail.

You might try isolating the various boards in the thing from the power rails. Seems to me ther are I/O jack boards, and maybe the controls are on two rows of three or four large boards. By pulling them from the power distribution individually, you might find one board has a problem.

COuld be a bad IC, but could also be a shot bypass cap. Almost every IC in the thing has a couple caps from the powr pins to ground. If one shorts, it drains that power rail. Can be a bitch to find among the hundreds. Visually I look for tiny black spots on them. You can also raise the voltage a little and watch for which one burns.

[fredo281]

Hello,
I'm new in this forum and my MX3282A is suffering the same problem than just described at the end by Pigyboy.
My intent to detect the bad board is to isolate :
1- I/O board channel 1 -> 12
2- control board channel 1->12
3- I/O board channel 13->24
4 - Control board channel 13->24
What do you think about this way of analysis by powering on for each step the mixer to finally detect the board wich is implicated in my issue ?
Is there any risk to create a worst damage by doing like that ?

In any case, thanks for anybody who could help me to understand progressively what is needed to do.
Fred ( From France )

[sidiri3561]

sorry to bring up an old post my question is for anyone out there Im a rooking so I really dont know how to operate any board at all, but I got a Eurodesk 3282a and it seemed to be working fine, it really did sound great, but from one day to another, I plugged everything in normally, started playing, and all of a sudden the sound cut out, the board didnt loose power, everything remained working, but it just hummed, I powered it down and then restarted it and it worked fine, a few minutes later it did the same thing? could anyone help me or give me any advise besides purchasing a new one