Dire problem with analog mixing console

T

TrueDatNOLA

New member
Hi all, new member here, thanks in advance for your desperately needed help.

I have an analog mixer that I believe is from the 90s. It's an Aries 24.8.16 console. I've had it for a few years and have been pretty happy with it overall. However, I recently moved to New Orleans earlier this year, and I've had the mixer in storage since mid-February. I just pulled it out of storage this week, and after getting everything set up, I powered it on and am now experiencing a strange problem.

When the mixer initially powers up, all the peak indicators light up and the VU meters on each channel pin to the far right at +5 db. After a minute or so, this seems to go away; all the peak indicator lights turn off and the meters settle back to the left at -20 db, all except channels 5 and 13. If I leave the mixer on for a while, eventually channels 5 and 13 return to normal, but if I plug a pair of headphones in, channels 5 and 13 start peaking again and a loud buzz comes through the headphones. I also have a pair of Yamaha NS10s driven by a Crown DC300a amp, and when I plug them in the buzz comes through the monitors as well. This buzz is happening with nothing plugged into any of the channels, and all the faders and gain knobs set at 0.

Any idea what could be causing this issue? With this loud buzz the mixer is completely unusable and I don't know what to do about it. Any suggestions are greatly appreciated, thanks!
 
Just a guess, but it worked before? Then got put in storage? Leaky caps?
Maybe some rough handling and a ground ir board damaged.
dunno, just pulling straws and bumping your thread.

The other thing that comes to mind is corrosion. New Orleans is a pretty humid climate from what i understand. Maybe in storage some contacts got corroded.
Good luck.
 
If all the channels are affected, I'd suspect something in the power supply, like a dried out filter capacitor. But if 2 of the channels continue to give off the problem then it make it less centralized of an issue. I'd still want to test the power supply first to see if its outputting the required voltages and look at their waveforms on an oscilloscope to see how pure or un-pure their DC voltages look. You might want to have a look inside the mizer and see if anything looks corroded on any connectors that deliver power to the channel cards and clean those up with some deox-it contact cleaner or just re-seating those harness connections to clean them via the action of plugging and unplugging them a few times which will also clean the contacts.

If you don't have these tools or the experience to properly trouble shoot this kind of stuff, you might be better off to just seek out a qualified service center and get an estimate rather then do a bunch of stuff that you're unsure of and/or accidentally make thing worse.



Cheers! :)
 
Caps shouldn't really fail in 20years, 40 more like. Then again the mixer could have been abused, run poorly ventilated for a long time?

Does sound like duff capacitors though, the reason only certain channels are affected could be because some mixer designs fed low voltage AC to each strip and rectified and filtered it locally. Why? It beats grounding problems.

The fact that you are asking here friend tells me that you are not qualified to fix it (WTGR!). Hunt up a tech' but be prepared to shell out some serious shells. Maybe time to look for a new one?

Dave.
 
^^^^^^^ Yes this is true. Asking a question usually does not make one a technician.

But that never stopped me. I'm a fix it kind of guy. With enough basic knowledge a person can dive into something they know nothing about and just by studying it and asking the right questions, and doing research, get a result.

I've fixed many an item that I knew nothing about in the beginning

With today's information age, there is almost nothing that cannot be learned.

It's all on the student.

The OP took the first step
 
The very first think I would do is test the output of the power rail that powers the meter drivers. You have schematics? You want to ascertain with power supply that is and then put your audio-bandwidth rated meter set to DC voltes on the regulated output of that supply and see that it is close to what its supposed to be, then set it to AC and test the same thing. At the most you should mV AC in the single digits, or ideally 0mV AC.

That's a precursory check. What I suspect is the culprit is poor grounding to the meter driver circuit. If you don't have schematics, get access to the component side of the meter driver boards and identify which pin of the opamps drive the meters and the peak lamps, and find out their ground source. Once you've got that start tracing back from the opamp ground leg to different points further and further away from the opamp and see what the resistance is. I suspect you'll find a point of high resistance.

I've run into this issue twice: once when trying to reverse engineer the power rails for the meter bridge on my prototype Tascam console (meters and peak LEDS would peg on power up and stay there), turned out my reverse engineering of the ground scheme was wrong...fixed that with some help and they work like a charm. The second time was with a Soundtracs MX-32 console. Wit guidance I had *completely* redesigned the entire ground scheme. The digital meters, when the console was powered, would slowly start crawling up without any signal present. It was creepy and bizarre. Turned out I'd neglected to include a necessary ground path in the new scheme...didn't realize that the elimination of a ground path with unnecessary facets also eliminated the necessary ground path for the meter drivers. So I created the proper path while still eliminating the superfluous paths that brought risk of ground loops.

So, check that/those power rail(s) for proper DC amplitude and for absence of AC components. If they're okay, then start checking ground path to the meter driver opamps. If you have schematics and can email or post that may be helpful.
 
I'm not a tech either, but I might open it up, do a visual inspection and reseat any ribbon connectors. I might also meter some obvious power supply stuff and double check any obvious ground points.
 
Oh! By all means have a go if you want to! You can probably do little harm by opening the mixer up and checking ribbon cables and other connectors. Note that many connectors are "keyed" to their mate. Clean with De-Oxit.

If the mixer has jack inserts pay particular attention to the switch contacts (and if mounted directly onto PCB look for bad joints). Plug in a jack and trap a tiny strip of 800grd wet&dry folded over in each contact, pull out. Repeat this several times and finally wash out with D-O.
DO NOT try to force anything into the contact to clean it, you will bugger the switch.

My reservation is based on the fact that unsoldering parts from PCBs is a skill and if the board is well buggered it is going to cost even more to fix and in fact most techs won't take on such work.

Dave.
 
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