Ghostbusting in a Mackie 8 bus

[jmann]

I was just gifted a Mackie 24*8. Yay! A free console!

However, upon first inspection, there's a weird, intermittent crackling that seems to happen on the master bus. (Any audio I've sent through it, on any channel, cuts out intermittently.) It also seems to happen occasionally with light bumps/touches on the frame of the mixer. And the meters intermittently blink at -40 (across all 8 busses) even with no audio coming through.

A quick Google implies that the ribbon cables are a potential culprit, so I'm psyching myself up to dive into this thing. (I've never opened a mixer before.)

But... anyone out there got advice for me? I don't want to put a ton of time and money into something that isn't really worth it. But it would be cool to at least try using a real console in front of the DAW (which I have never really done before.)

FWIW, I'm not imagining relying on the Mackie preamps or EQ, just thinking it could be nice for routing audio, providing cue mixes w/out latency, etc.

[KuruPrionz]

It could be the connectors for the ribbon wiring but before you got deep, try the easy stuff first.
FWIW, I am no electronics tech, just a busy musician with a history of guitar repair and an inclination to get things working if possible.

First, work in a well ventilated area. Some of us use the vent fan on the stove/oven or in the bathroom, outdoors would be better if it's warm enough. There will be fumes that you do not want to breathe. Nothing wrong with getting a painter's respirator either.

If your mixer has been sitting for a while or even if it was used but not a great deal - unplug the mixer and do the following:
Turn each and every knob and fader all the way up and all the way down briskly (but not violently) at least a dozen times or more - more is usually better.
Then switch each and every switch in and out a dozen or more times as well.

Now plug the mixer back in and see how it behaves. Test audio and listen for scratchy pots or switches. If there are none and the mixer still misbehaves, you can go deeper. Buy Caig De-Oxit and get their pot cleaner as well. Open up the mixer and clean every pot and every fader to the extent possible using the correct De-Oxit for the job, pots will use a different type than switches. If the ribbon connectors are easily removed or just need a bit of gentle persuasion, do that and spray both the pins and the female side of the connectors with the correct De-Oxit. Plug/unplug a few times while the chemical is working.

After every possible pot/fader/connection point has been carefully cleaned with De-Oxit, put the mixer back together and try it again.
Most of the time, it will be happy again. If not, it may be time to send it on it's way or ask a techie friend if you have one. Personally I don't have the technical skills, the inclination, the facility or the tools to tackle anything beyond that but most electronic gear just needs a good cleaning every so often and that may be the entire problem. If nothing else, you will learn things that will be useful as you go. Cheers, Kuru

[winky dinglehoffer]

I agree with Kuru that exercising faders, switches & pots can help with a lot of weird problems.

As to the ribbon cable: what is the common problem? Is it that they get loose & connections get intermittent? Or is it a problem with the cabling itself? Or some other issue with the cabling & associated connectors?

[jmann]

Thanks, I'll try that thorough cleaning, for sure. I think this thing has been sitting still for years. Maybe even decades.

As for the ribbon cables, a bunch of different Gearspace threads indicate that Mackie did a lot of replacing of the ribbon cables when these things were new, including many under warranty. They got up to a Rev. G of the cables, I believe. So maybe the cables themselves were faulty? I have no idea if anything on this board has been repaired or replaced, though.

[Magnetic Services]

Simply disconnecting, cleaning and reseating the ribbon cables might be an easy fix!

[jmann]

Yeah, trying that now! Thanks, folks!

[KuruPrionz]

I neglected to mention the jacks but clean all of them, including the plugin for the power supply if there is one.
Long overdue anyway, no harm done if it doesn't fix anything but it may just sound better with clean jacks.

[The Scum]

My recollection of that issue is that the ribbon cable connectors have different alloy plating on the contacts.

It might be that the originals had an alloy that tarnished, or that the male and female portions used different alloys, and a bimetallic reaction caused corrosion.

If you've got a bench vise, it's pretty easy to make your own ribbon cables, should the need arise. Gold plated contacts would be recommended, as they're less susceptible to those problems.

[Scodiddly]

If reseating the ribbon cables helps, then adding some DeOxit D5 will be your next step. That was a pretty common thing to do when people were still bringing those things in for repair. You should also try plugging and unplugging a few times in every insert jack - the normalling connection needs exercise too.

Sometimes though just the vibration of being thrown into the back of a station wagon and driven to the shop would clear up a lot of little problems, though. A lot of those A&H mixers just sat in churches and theatres, accumulating oxidation gunk on all the contacts. Gear that gets moved around a lot has different problems, but rarely the same ribbon cable issues.

[digitaldrummer]

It might be that the originals had an alloy that tarnished, or that the male and female portions used different alloys, and a bimetallic reaction caused corrosion.

That's a very common problem in the world of ribbon cables and other cable connectors. reseating them usually "fixes" them for some period of time but they may oxidize again down the road. Cleaning with DeOxit and then applying some of the Deoxit gold (or even the D5 red stuff) can protect from (or at least delay) further oxidization.

[jmann]

Good to know. I opened it up and applied Deoxit to all the ribbon cables that were accessible without fully disassembling the thing. (There must be some I can't see on top of the PCBs.)

I also exercised every single knob and fader, and applied Deoxit to every singe jack, then worked a TRS cable in and out of each 8 times. (The History of Rock Music in 500 Songs podcast is a perfect accompaniment to this kind of thing.)

Now waiting for it all to dry out a bit before I fire it up. If this doesn't work, I will fully disassemble it and clean everything. But cross your fingers!

[jmann]

OK - minor progress. I am using a -20dbfs tone from my field mixer to test things. Also Spotify from my computer on 1/4" TS inputs.

I can now solo up the inputs and set a level! So that's good. And the periodic meter blinking seems to have stopped. I can hear the audio clearly when it's solo'd, but not through the buses (master or any of the submixes.)

I can send audio out through the Aux sends, so those are working. Seems like I've got more cleaning to do (or ribbon cables to re-seat) in the master section somewhere. Unfortunately that will take a lot more dismantling than my first try. Still, seems like we're moving in the right direction.

[A.David.MacKinnon]

OK - minor progress. I am using a -20dbfs tone from my field mixer to test things. Also Spotify from my computer on 1/4" TS inputs.

I can now solo up the inputs and set a level! So that's good. And the periodic meter blinking seems to have stopped. I can hear the audio clearly when it's solo'd, but not through the buses (master or any of the submixes.)

I can send audio out through the Aux sends, so those are working. Seems like I've got more cleaning to do (or ribbon cables to re-seat) in the master section somewhere. Unfortunately that will take a lot more dismantling than my first try. Still, seems like we're moving in the right direction.

If there are inserts on the master bus try cleaning and exercizing them first.

[KuruPrionz]

Cleaning and working the send/returns is good. Try putting a short patch cable in the inserts, from send to return. Sometimes the switch in the return jack gets corroded and won't provide clean signal.

[jmann]

Success! I think opening up and re-seating the ribbon cables did the trick.

I still see a little of the phantom meter activity (on louder passages/bass there are occasional blinks of the -40 meter lights across all the submixes), but the audio is routing properly and sounds good.

Seems like I'll need to totally dismantle and clean it some day soon, but in the meantime it actually functions. Now, to see if I actually enjoy working with a console....