problem with behringer MX3282A.... please help!!

[didjital]

I bought a used behringer MX3282. everything works fine except I get no signal on the master bus or control room outs. Also the meter doesnt light when monitoring the master, but soloing channels and busses makes it work. I have signal at the master inserts--- which confuses me. The guy I bought it from said it worked fine (I know, I know)--- but its making me wonder if some internal cable became unplugged in shipping? Ive been using bus 7 and 8 as my master, so I do have a work around--- but Im losing all the control room features which bugs me...

[didjital]

I forgot about this..... one iof the input channels stopped working one day. The -20 green led looks right, but no signal at fader. Then I messed with the eq...... when the low band is anywhere above 0, the channel cuts out. when its at the center 0 detent and below the channel has sound and the low shelf lowers properly, but there is distortion. Is this something I can fix?

[Jazz P Bass]

Unless someone was inside the mixer, I highly doubt that any connector came loose.
Behr. has redefined the overuse of a glue gun.

[didjital]

Any ideas on where to start looking then?

[Jazz P Bass]

First off, have you looked at the schematic?
It is 55 pages long.
Second, the circuitry utilizes surface mount technology.
Extensively.
So, to repair the mixer you will need to be able to 'read' the schematic.
Then you will need the tools to troubleshoot the problem & the equipment & skill to repair it.
Please understand that I am not dissing you.
I do not know what skill level you are at, nor do I know what tools you may or may not have.
So please look at this post as seeking answers rather than being a critique.

[Enzo]

+1^^^^^

The mixer is laid out on large boards, the ribbons between boards are mostly major busses, grounds, and power supply. Y guess it is possible the cable to the insert jacks is faulty, but seems unlikely to affect only those pins.

You L/R mix buses come from the channel assigns and the sub assigns as SUBMIX_L/R (L and R are separate, I combined them for ease) That buffers through IC62 to become MIX_L/R. Through IC63 to the insert jacks, then the fader, then buffered through IC77 to become MASTER_L/R.

That signal is what appears on the MAIN out L/R jacks, separate op amps then take that and make a balanced out on the XLRs. MASTER is also what feeds the meters as well as the monitor circuit. SO if signal does not reach teh MAIN output, it won't see the meter or control room either.


The main bus comes out the inert jack OK? That should be on the tip, so plugging all the way in should get it. The return is on the ring, so you have to gently plug the signal in half way to get that to come out the MASTER. COnceivable both jacks failed, but less likely. But try that. Or use a real insert cord. One way or the other.

So run a signal, it comes as far as the insert jack. Does it appear at the main faders? If not, find out why, there is not much between the two points. If the fader has signal, then the only thing betwwen that and the output is IC77. A quick check there is for DC on pins 1 and 7. The chip can fail without that, but more often than not, bad ones put a rail on the output.


Worry about channel 20 after you have the master section working.

[didjital]

Any idea where I can get the schematic?

I have signal at both insert jacks for the mains- I was using an insert cable to run to a compressor so I could see signal on the comp meters. It all worked fine, just not getting to mixer meters or output. When you say to check for signal at master faders, you mean internally with a meter?

[Jazz P Bass]

Behringer MX3282A Schematic: Behringer MX3282 - Electrónica - Esquemas - TV - Áudio - Digital
Schematic link courtesy of fellow member Vintagekiki.

[Enzo]

I understand it comes OUT the insert jacks, what we need to do is apply a signal INTO the insert return.

As to checking the signal at the faders, yes, I mean inside. Very hard to work on them from the outside.

That is why in post #6 I described the signal path and the ICs is flows through. The signal from the insert jacks goes right to the faders. SO you need to find where along that path the signal is lost. Scope, AC voltmeter. signal tracer. Whatever means you have, you have to determine how far the signal gets. When you find the circuit element that signal cannot pass through, there will be the problem.

The meters and control room draw right off the master output, so if the master output does not have signal, neither will the meters and control room monitor.

[didjital]

Thanks for the schematics

Sorry for sounding so stupid- I'm just making sure I'm understanding what you're saying....

I'm gonna pop that baby open in the morning! I do have experience repairing lasers.... First time with a mixer though.... Thanks for the info. I'll get back and let you know what I have found, in case you're curious.

[SHORT EDDY]

If that's the mixer that I think it is, the faders are designed so the wiper goes right down to the bottom corner of the resistor strip when the fader is down all the way. All it takes is a few crumbs from a fried chicken wing falling into the slot, then the next time you move the fader to the bottom, it scrunches up the wiper fingers, destroying the fader. Those boards aren't very desolder friendly either. There is a reason that their stuff is dirt cheap. I've found that scrunched up wiper fingers cause lots of neat problems.
I won't even work on that brand of gear any more. Lost count of how many times I replaced fader pots in a single mixer. Then spend that much time again repairing damaged traces. You practically need a hydraulic press to remove the pots once they're desoldered. Just say no to Behringer. (my opininion)

[SHORT EDDY]

I decided to check and it IS the same mixer. CHRONIC fader failure. First thing that I would check with that mixer. Look for crumbs down in the slots...Have fun!
Oh, if you ever do get it back to 100%, you might want to limit the sliders from going all the way to the bottom. It will happen again.

[km6xz]

The faders and pc boards are not hard to work on at all, but you do have to have the right rework gear or at the least use Chip-Quik low temperature solder on any part that is soldered on both side of the board. Board and part come out in seconds with no damage. It is an indispensable tool at about $14. Removing large ICs without damage, just one of them, will save more than a year's supply.
Overall, after my shop working on literally tens of thousands of Behringer units when we were one of only 2 service centers in the US I got to like how easy they were to repair and how well the pc boards held up. They are not bad pc boards and their soldering system was rather reliable. It was less common to find bad solder joints than bad ICs or pots. Mechanically, most of the products were as light as they could get by with but the pc boards were solid. I would rather work on SMD than point to point or thru-hole because it is really hard to damage a board or trace. It is very rare that a SMD part has a cracked solder joint because of their small size means little mechanical stress when thermal cycled or due to vibration.
During that period we were also the sole factory service for Alesis back before the bankruptcy when they were flying high. That meant we got all the units sent back to the factory ended up on pallets and trucked up to us. There were warranty stations at the time so if one got in over their head on a M20 or XT, we ended up with that one also. So we had a scope of view to compare. The pc boards were no where as damage resistant as the Behringer pc boards. We got a lot of warranty independent-shop damaged boards to rework which was not as quick or easy as repairing a Behringer pc board. Comparing the reliability of the Alesis mixers to the Behringer mixers, was an easy choice. Behringer sold 10's of thousands of any model and got hundreds back during warranty. Alesis sold thousands and got back hundreds under warranty.

[SHORT EDDY]

I thought that I remembered having problems with getting the pins to come out of the holes even after they were clean and "cracked loose". The problem was the pins were a tight fit in the holes and wanted to pull the pads and cores out. It is possible that I've mixed that experience up with another unit. (thanks for the desoldering tips)
The faders that constantly fail is certainly a feature on that model though. It's a great sounding, very functional desk for cheap...while it works. Might be a good budget mixer to keep clean and covered in a studio but it won't (didn't) hold up in a typical club environment as a house mixer. A new mixer, and after three years the club owner couldn't get $125 for it. Resale value says a lot too. I actually mixed on that board and liked it. It just doesn't hold up at all.
You must be aware of the chronic failure problem with that model? (and any other model that uses that fader design)

[km6xz]

The MX9000 used the Panasonic 100mm faders which are considered the best low cost pc mount faders and was one of the reasons Mackie claimed was justification for suing Behringer over the MX9000 being a "copy" of the 24x8 Mackie. The complaints claimed that Mackie had an exclusive right to the Panasonic fader which Mackie was basing some of their PR effort on. The judge in the case thought the claim was strange so not being an engineer, he started looking at parts catalogs to see what was the norm in the industry. Apparently the lawyers did not bother to check their own fact because the judge found the Panasonic fader was available to anyone, including Behringer, who ordered from Digi-key or any of a hundred different supply houses. There was also a claim that Mackie had a specially designed 60mm fader that Behringer was illegally using because of exclusive rights to, which turned out to be a standard line item in the Alps short form catalog. Behringer used Alps on almost all their mixers except the 100mm used in the Mx9000. They are both very reliable and closely trimmed faders but as mentioned, the 100mm Panasonics are very tight in tracking balance and position accuracy. So the 3282 used a cheaper less exacting fader but so was Mackie and most others making small form mixers. Some use the Alpha faders which are not as accurate as either the Alps or Panasonic in my experience so the active component quality for transistors, ICs and moving elements like linear faders were pretty much like everyone else's of the better small mixers except the MX9000 which used better than normal faders. I have found the Alps to be fine and only suffer when abused, like all linear faders and other than due to spills or physical damage, seldom needed replacement.
One of the reasons the Behringer pc boards get high marks for construction is their resistance to intermittent solder connections. Surface mount is mostly the aid there but the few components that do use thru-hole placement have little room to spare around the lead which is also an aid to keeping solder joints solid. That tighter fit is not stuck, just little room for slop, so if desoldered well, with appropriate heat localized to the joint is applied the part comes out easily without damage. That applied to highly heat sinking connections such as ground planes where solder flows on both sides of the board.
You can pre-heat the board, they will handle in excess of 250c with a pc hot air stand or wand or using very low temperature solder for low temperature removal. I prefer the latter method if there is any chance the part might be used again. The whole desoldering job of, say, a dual gang pot with support solder tabs, that is mounted with heavy ground planes top and bottom is capable of damaging any pc board is done with a big iron or solder gun. The Chip-Quik method only requires bringing the joint up to about 50C so when done, the part and board hardly feel hot to the touch, and the part just falls off without prying.
De-soldering stations and re-work stations used to cost over $1000 but there are Chinese systems that are well within the reach of any part time repair shop. It is a basic tool of the shop, no less important than a DVM or scope. A local parts house here was having a sale on a unit from Ya Xun brand that had a vacuum pump de-soldering gun head, a hot air head, soldering iron and an integrated heat stand for $400. Few need all that, however, a vaccum desoldering station can be had for $140 and hot air head and control box can be had for $80. It is not a repair shop unless it has the basic tools of the craft, even for tube-only shop that can't or won't work on contemporary electronics needs to be properly equipped or the customer is being slighted and risks having the value of their unit lowered by less than professional treatment of his gear.