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I have a Mackie 32x8 8 bus mixing console in my shop for repair.

On 3 channels the lower part (HI and LO EQ) of the 7 EQ pots aren't working at all. And on another channel any manipulation of both the EQ level pots results in a high volume fixed tone.

Anyone had the same issue before? And knows how to fix it?

Also, the output section is quite noisy at startup and the LED display of the L/R main out doesn't seem to receive a signal although when powering the console up it is working but just for a brief moment.


MrEase Tue, 11/23/2010 - 04:11

Does it smell of beer? It sounds like there are so many problems here that something like this has happened. I would first try a thorough cleaning of the PCB's and checking out the power supplies with such mulitple problems. Other than that, just apply the usual fault finding techniques as I'm not aware that what you describe is a "typical" problem for this mixer.

Boswell Tue, 11/23/2010 - 08:13

I saw you had been asking about this on the SOS forum and that you had got the usual helpful sort of advice and opinion from them. In their wisdom, they did suggest to look for problems with the internal cabling and connectors, which I think is a good place to start.

Are the three channels with the similar EQ problems adjacent or scattered? This could be connections, or it could be a problem with the switching of the Hi/Lo EQ to the Mix-B channels. Check the "Split EQ" switches.

The output section being noisy until it has settled is likely to be a separate problem with coupling capacitors going leaky. The L-R mix display problem may be another connector issue.

TheJackAttack Tue, 11/23/2010 - 08:49

While you are in there you should beef up the power supply if this is an older board. That was a failing of the older non Onyx 32 channel boards. Also, those older boards were known to have ribbon cables go bad or pins oxidize. After following the very knowlegable advice above you might swab each of the ribbon cable connectors with some Deoxit. In the FWIW category, Mackie will still service these or provide parts for purchase.

dvdhawk Tue, 11/23/2010 - 09:16

Boswell's note (as always) is a good one, the Mackie's B-Mix buttons have the capability to split the EQ rendering the Hi/Lo to the B-Mix - so make sure you monitor the B-Mix output too. So if this isn't an 'oops, pushed the wrong buttons thing' - it still gives you a place to start testing the mechanical switches that split the EQ.

I own a Mackie 32x8 since they first came out, and thankfully have never had to take it apart. I don't believe they're modular at all, just one big flat PCB nutted to the chassis I think. So it's gotta be an hour's work just getting it apart enough to replace a fader or switch. Maybe you'll be able to tell me different. [I'd also be curioius to know if they're surface mount op-amps, socketed full-size IC's, or full-size IC's soldered directly to the board.]

Anyway, your problem doesn't sound like some random component(s). It sounds like something catastrophic happened to the board to me. Which is the usual suspects; if not liquid causing a serious short, possibly lightning damage (or other surge), possibly it's been dropped and there's a crack in the PCB traces in the affected area. It sounds like something significant happened as the other gentlemen have suggested.

As for the tone generator problem:
I recently worked on a 32-channel Soundcraft LX7ii from an installation that was damaged by lightning. The lightning didn't damage the AC power supply, not so much as a blown fuse. It hit a portion of the building 90 ft. from the soundbooth, but apparently fed a static surge back through their low-voltage wiring (mic jacks, etc) somehow. Any channel on the mixer that was connected to a floor-pocket or wall plate XLR from the corner of the building got killed.

In testing the board I found that when the phantom power [switchable in groups of 4] was on, one of the channels became a tone generator. The other channels were damaged in some oddly regional ways - not unlike what you're describing. Some channels passed no signal at all. Some would produce a very distorted signal. One was a low level white noise generator. In addition to a number of diodes, resistors, etc. the surge blew up a variety of surface mount op-amps, literally, as in tiny shrapnel. In the Soundcraft the input boards come in 8-ch modules which are separate from the circuit board with the EQ and fader circuitry. All the damage was isolated to the input board, and six of the seven damaged channels were on one input module.

If you're still stumped call Mackie tech. Some of those guys can be very helpful.

Good luck.

PhantomBox Tue, 11/23/2010 - 12:04

To MrEase:
It doesn't smell like beer anymore, but in fact someone spilt something on the console (just above the faders) and one of the PAN pots got stuck. I managed to disassemble the pot and got it going again.

To Boswell:
Excellent point. I'll check the SPLIT-EQ switches. By the way: the L/R-mix display did in fact work until I took out the master-board for cleaning...

To TheJackAttack:
I used very high grade alcohol for cleaning. Deoxide is not available where I live. And Mackie is far far away...

To DVDHawk:
Checked: B-MIX buttons.
Mackie's 24x8 and 32x8 8-bus consoles are assembled on boards of 8 channels each. ALso, they use 8 pin 4560L (or 9 pin 4560S) single-in-line dual OP-amps. And they are non-socketed (@#$*!). In some cases (i.e. the EQ "daughter boards"), they use microscopic surface mount OPs.

RemyRAD Tue, 11/23/2010 - 12:24

To the best of my knowledge Mackie boards have 8 channels per circuit board. Everything is surface mount and nearly impossible to repair without specialized equipment and lots of experience doing it.

Edge connectors along with their associated ribbon cables are always a source of problems due to airborne particulate dust pollution/smoke, etc. Frequently, you can fix these problems by simply unplugging all of your connections internally and then re-plugging them back in.

Your huge boost in level, and those couple of channels, without any equalization would indicate to me that the feedback loop within the Op-Amp gyrator equalization network has lost its feedback loop reference. So level goes through the roof when an op amp operates without any negative feedback and of course with that, no adjustable equalization will occur.

When you start having these kinds of problems with these low-cost, all surface mount consoles it's a good thing you have 32 inputs. That way, you should always have it least 24 good working inputs which is all you really need. And these particular types of boards, when it comes to repairs are really, throw it out and replace it types of repairs. Meaning that, you're having trouble on channels, say, 3 & 4, you'll have to replace 1 & 2 along with 5 through 8 to get a working 3 & 4. To most folks, this doesn't make much sense and so these are frequently referred to as "temporary disposable consoles". That's how you keep the cost of manufacturing low enough to make it affordable for everybody. Rebuilding a 1970s Neve console is easier than repairing a Mackie. You pay for modularity. Nothing like swapping channels 6 with 18 to make sure that the problem you are having in 6 is in the module. That makes for some pretty quick diagnosis's's's's. Effects send 2 not working on module 17? Swap it with channel 5, etc. Can't do that on a Mackie or most others. Sounder Craft was one of the few exceptions as they were semi-modular. You could remove entire channel strips. Having these kinds of consoles makes you a much better technician in the end. Simply because troubleshooting is much easier and more convenient. That's not to say you should get rid of your Mackie but you may have to compromise and work around some of the problems eliminating channels that don't function well. That's what masking tape is for. You just cover all of the knobs on the nonworking channels and no sweat. Try to fix it? And you may do more damage than good especially in a surface mount world.

Eyes of 55
Mx. Remy Ann David

Link555 Thu, 11/25/2010 - 05:40

SMT is not impossible to repair, I find it easier. Heat gun with nozzle works well me. And just for the record, just because a designer uses SMT does not mean the design is cheap or inferior. A good design is a good design. SMT allows closer positioning of components for the shorter lead lengths. I am not saying mackie's 8 Bus was an inspired design, but it wasn't the fact that the op-amps were SMT, that made it the way it was.

RemyRAD Thu, 11/25/2010 - 12:01

And one that you just throw out once things start to go south. Which is actually fine in our current disposable culture. But for those that want to fix their mixer/consoles, fixing SMT is an art. Heck, most folks can hardly solder a 1/4 inch or XLR. And you want them to fix SMT on their Mackie or Behringer with your hairdryer?

Yes, Greg Mackie made a low-cost goof proof box that the average Joe could never repair. Of course you cannot fix API 2520's either because it's like Col. Sanders 11 secret herbs and spices. But you can fix my Neve BA 438/440's, etc. easily. It's just another method to raise overall quality, while lower manufacturing costs and in today's economy, that makes sense for businesses. Unfortunately, the low/no budget entry-level guy has saved all of their paper route money to buy this low cost mixer probably, won't have the skill nor the financial where for all to have it fixed by a skilled professional. And that's the sorry state of SMT. I've been soldering things for over 40 years so I've gotten kind of good at it. I've got no desire to play with SMT. Too much opportunity to destroy what you're trying to repair.

If it's broke, don't fix it.
Mx. Remy Ann David

RemyRAD Fri, 11/26/2010 - 10:50

I'm afraid of it because I've had to work with it from time to time. Tinier & smaller parts as you get older becomes rather counterproductive. Again, it's probably because I'm old school? I'd rather have to repair a circuit board trace (done many times) than trying to solder fleas to circuit boards. Maybe it's because one of our kitties caused us a flea infestation and every time I look at surface mount components I think I'm seeing fleas? Eek! Very difficult to kill fleas with 25 W soldering irons. And of course you can't use those things on SMT boards. I just don't have the right technique yet. And I'm really not sure about cultivating it?

Fleas pop when you solder them
Mx. Remy Ann David

jammster Fri, 11/26/2010 - 14:35

Too bad everyone ripped their (Mackie 8bus) design and then the company sold out and became publicly traded.

Still, everyone does what they need to do to survive in the Business I guess.

Mackie still makes great stuff, most of the higher end (Onyx) is quite competitive in todays market. Still, I just hate the idea that most of todays budget gear is made in China, but thats just me.

You can still find awesome deals on old vintage soundcrafts if your persistent. This summer I found a Soundcraft 600 series modified by Jim Williams of audio upgrades in California for $500.

I ended up driving 1600 miles round trip, from here to Cincinnati to pick it up! Its modular heaven! :)

RemyRAD Fri, 11/26/2010 - 16:44

Yeah, about that Chinese thing... When was the last time somebody saw an advertisement for Studer consoles? Do you see there website address? http://www..Studer.CH that ain't Switzerland? I guess Dr. Sidney Harman is building Studer consoles in China?? We don't need no stinkin' Swiss precision no more. No more. Or anymore. Nevermore? Anybody quote any ravens lately?

Braaaaach (my best raven impersonation)
Mx. Remy Ann David

PhantomBox Sat, 11/27/2010 - 06:56

Just for the record: I usually work on this high end stuff also: Harrison, Amek, Sony, MCI, Midas, Quad Eight, Telefunken, EAB. All NOT MADE IN CHINA. I take them apart and rebuild them in sets of pairs, making the chassis from scratch, the PSU and all connections (inputs, effect loops and outputs).

And by the way: the Mackie console was made in 1993. Still a teenager.

Boswell Mon, 11/29/2010 - 08:00

PhantomBox, post: 357753 wrote: The EAB are the oldest ones of all. They feature 2 tubes E283CC each. I guess they can be replaces by 12AX7 tubes with modifications to the tube socket's pinout. Still figuring out how to make the PSU.

Well, since I cannot get the 22000uF capacitors I guess 2x 10000uF will do it. Any suggestions?

You would have to re-wire the pins on an E283CC socket to take a 12AX7/ECC83, but the result of fitting the non-specialist part may be that it does not sound as good. However, it's worth checking that the original valves (tubes) really were E283CCs and not just marked as such. On a true E283CC, the shield fitted between the two triode sections is clearly visible, and this is wired to pin 7. In case you are interested, suppliers like MachMat (Holland) boast that they have genuine E283CCs in stock.

What working voltage are the 22mF (22000uF) electrolytics that you are looking for?

PhantomBox Wed, 12/01/2010 - 09:07

The noise at startup was definitely the PSU. I replaced the 22.000uF/35V caps with 2x 10.000uF/50V and one 2200uF/50V each. And another 2200uF/100V for the phantom power. Noise is gone.
Now I don't know what happened but the L/R meter LEDs do work again but the main fader doesn't. Volume won't turn down at all. And I didn't touch the master PCB.

Tom Fodor Sun, 02/19/2012 - 05:18

I think that Mackie had the right idea. You can pay some tech a $150.00 surcharge plus $80.00 per hour to hunt down a single dead component on a board, source a part and then solder it in and test it for you, or you can just pop the sucker open, drop in a whole new board and off you go again! No messing around and roughly the same cost involved. The up side is, you got a whole new PCB in there, not one that's had components frying and stressing other components around it. It's still a semi modular design and I think the replacement to repair cost argument went out the window when the 8 bus was introduced. Great little console for what you paid for them, and ten times more reliable than the new "fully modular" Toft ATB consoles. They might have a slight sonic edge over the 8 bus, but we are talking about a 20 year old console here that cost half as much new. The 8 bus deserves to be recognised as a serious milestone in music production history, the day average Joe got to make a hit record in his garage.