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This project has been on my radar for a while, and the time has finally come... The Mackie 1604 VLZ3 is a really great audio mixer, but this particular one sat unused, collecting dust for several years. That layer was thick and, in retrospect, my approach to cleaning it up probably resulted in making some of the knobs (potentiometers / pots) sound scratchy upon turning. Oddly, the scratch is limited to only some of the white EQ knobs (the 100-8k range, highlighted below).
I cleaned up the dust layer by going over the board with a standard vacuum cleaner bristle brush, then used compressed air to clean the areas between the knobs, where the brush wouldn’t reach. DON’T DO THAT!!! My hunch is that the mixer worked perfectly, until all that dust got blown around. Instead, I really should have used a barely-damp paper towel and q-tip for surface cleaning.
Now, let’s explore fixing those scratchy EQs.
Tools needed:
cleaning spray (see details in the paragraph immediately below)
Phillips head screwdriver
small Allen wrench / hex key (size details explained below)
protective gloves, like latex or nitrile rubber
possibly end-cutters/pincers, pliers, or similar hand tool to remove knobs
optional but helpful: a muffin pan to keep the screws and knobs organized
About the cleaning spray, I’ve researched this topic thoroughly, and opinions about it vary. Some people recommend CRC Contact Cleaner. Others recommend DeoxIT D5 for all the internal components. Others say to use D5 on the pots and DeoxIT F5 or white lithium grease on the faders. Another cleaner is called Nu-trol. That tells me there’s no single, perfect solution, so I went with the cleaner cited the most in these conversations: the D5 spray (~$15).
In a pinch, some people have reported removing the knob caps from an otherwise-intact board and working cleaner into the pots from the top. That approach could make problems even worse, since it can work surface dust down into the electronics. Even though the disassembly and cleaning process is tedious, the thorough approach is really the best one.
So, to begin this teardown, make sure the board is completely unplugged - the power cable, instrument/mic cables, everything! From there, very gently put the mixer face down on a soft, clean surface. Remove the four screws securing the ribbon cable cover.
Next, pick a side and remove the three standard screws shown below, and the two with washers. Then, move to the opposite side and remove the same set of screws. When that's done, the patchbay will be free from the mixer housing.
Now it’s time to remove all the knobs. It’s tedious, with 171 of those, plus 21 fader caps on the board. If the knobs haven’t ever been removed, they’ll be snug. You can use pliers to pull them off, but clamping down on the plastic will probably cause some superficial damage:
Instead, I tried a pair of old end-cutters/pincers, which allowed me to grip the caps from almost their base, leaving less noticeable indentations.
Once those are off, carefully flip the board on its side. Out of necessity, I used a 1.5 mm Allen wrench to remove the tiny screws circled below, which hold the circuit board and housing together. The metric wrench wasn't a completely snug fit, but it's what I had available.... I've read 1/16 is the proper size. If you only have the 1.5 mm version, be very careful to not strip out the screws. Having the board on its side isn’t crucial, but I found it provides a little more leverage for this task.
When all the tiny screws are out, carefully put the board face down again. I have bad memories from my teenage years of accidentally destroying ribbon cables while trying to unseat them from old computers, so I Ieft these intact. Grab ahold of the circuit board from both sides, and gently pull it straight up, to separate it from the housing.
From there, turning the circuit board over and gently resting it against the patchbay offered a nice work area.
The next, best step is to clean each potentiometer shaft/arm/stem/post/whatever-your-preferred-term-is. These feel tacky, and I’m guessing that’s a design feature, to keep at least some gunk from getting worked down into the pots. Not wanting to use a cleaner that might remove the sticky stuff, I used my fingers and fingernails to remove as must dust as possible.
Now it's time to address those scratchy pots. Since we’re dealing with a chemical solution, it’s smart to wear gloves and spray in a well-ventilated area. This nozzle has three settings: low, medium, and high. Low is ideal.
To minimize overspray even more, I cut down a drinking straw to a few inches length...
This straw fit perfectly over each pot and kept the DeoxIT from getting all over. Even with the shortest burst possible and set to “low”, it was sometimes enough spray to overfill the pot and run down onto the board. A little bit shouldn't hurt anything in the long run, but the excess fluid definitely isn't useful, so I sopped it up.
After each spray, cycle through the range of these rotary knobs several times at a medium to fast speed, to thoroughly work the solution down into the pot and loosen up any dust inside.
When you're done working on the problem areas, let the solution rest for a couple minutes, before hooking the power back up and testing the mixer. Once you do that, be careful to not touch any of the internal circuity!
My initial pass of spraying the problem EQ channels got most of the scratch out, and a follow-up pass completely fixed it.
Keep in mind these cleaning sprays will thin out the mechanical grease in the pots, which provides some resistance when turning each knob. I wish the white EQ knobs on this board still had that smoother motion, but even better is having a board that sounds good again!
The reassembly process is just the reverse of disassembly. The circuit board fits precisely and snugly in the metal housing, and it took me a minute to get the faders and knob shafts lined up right.
After that, the tiny screws go back on, securing the board to the metal housing. At the risk of stripping the the screws, they should be snug but not cranked down.
So there you have it... If you have any questions about this process, don't hesitate to drop a line in the comment section.
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"Tech How-to: Mackie 1604 VLZ Sound Mixer Cleaning (Scratchy Knobs/Pots)"
by Justin Kilmer
All images and media on this site are © by Justin Kilmer, unless otherwise noted.
This tech how-to was written entirely by a human.
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