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  • Mackie Mic-Pre Issue

    I have a Mackie 1202 VLZ-PRO Mixer. One of the mic-pres doesn't output sound unless the trim is totally maxed. Anyone ever have this issue and know of a fix? Or a suggestion on what could be happening? Thanks.

  • #2
    I'm guessing the mic works fine on the other channels?

    The only thing I can suggest is getting some lubricating contact cleaner and give the pot a quick shot and work it.
    It may be worn and dirty. Give the input jack a cleaning too but don't get liberal and go spraying everything in there. Cleaning pots reduces the lifespan.

    You may want to check the solder contacts to the pot while you're in there too. Other then that there's little in there an amateur can do. Even a qualified tech may not be able to get parts for it. They don't make gear repairable to component level any more. Its either board swapping at the factory or the trash bin.
    Last edited by WRGKMC; 10-04-2015, 04:42 AM.

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    • #3
      Originally posted by WRGKMC View Post
      I'm guessing the mic works fine on the other channels?

      The only thing I can suggest is getting some lubricating contact cleaner and give the pot a quick shot and work it.
      It may be worn and dirty. Give the input jack a cleaning too but don't get liberal and go spraying everything in there. Cleaning pots reduces the lifespan.

      You may want to check the solder contacts to the pot while you're in there too. Other then that there's little in there an amateur can do. Even a qualified tech may not be able to get parts for it. They don't make gear repairable to component level any more. Its either board swapping at the factory or the trash bin.
      Huh, I was unaware of the lube decreasing a pot's lifespan. That's pretty much what I was going to do, but wanted to get some suggestions first. Oh ya, all the other mic-pres work fine. Thanks.
      Last edited by Adam O'Blivion; 10-05-2015, 10:49 AM.

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      • #4
        Originally posted by WRGKMC View Post
        I'm guessing the mic works fine on the other channels?

        The only thing I can suggest is getting some lubricating contact cleaner and give the pot a quick shot and work it.
        It may be worn and dirty. Give the input jack a cleaning too but don't get liberal and go spraying everything in there. Cleaning pots reduces the lifespan.

        You may want to check the solder contacts to the pot while you're in there too. Other then that there's little in there an amateur can do. Even a qualified tech may not be able to get parts for it. They don't make gear repairable to component level any more. Its either board swapping at the factory or the trash bin.
        I just unscrewed the back panel and there's a secondary PCB board blocking the pots. It doesn't seem that obvious on how to remove this PCB board. Before I tried opening the unit, I tested all four preamps and this time hey all worked fine; the trim pots are just filthy. Here's a pic of the inside if I'm not explaining it correctly:

        Does anyone know how to get remove this top piece of PCB board and get it out of the way?

        Thanks,
        -Adam

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        • #5
          Cant see it that well, but you may have to get in there from the top side, and yes that would likely require pulling every knob off the control panel and likely unscrewing all the hex nuts holding the pots to the top panel.

          The boards may also have some screws to hold them to the top panel too.

          There may be one short cut you can try. It doesn't always work and it can work in 50% of the cases in limited degrees.

          Pull the knob off the trim pot, pull up slightly on the pot shaft and try and force some cleaner down the shaft of the pot from the top.
          You have to work the pot and do this over and over to get enough down the shaft onto the rotary connectors that make contact with the carbon pad.

          Like I said, this is messy so use a paper towel or cloth to surround the pot and catch any extra fluid.

          Lubricating contact has mineral oil in it to lubricate the pots. It will creep too so getting some down that shaft may take a little time to work. you do have to work the pot turning it filly left and right maybe a couple of dozen times. You can usually feel them loosen up as the mineral oil gets in there. Its just hard to know if its getting on the contacts too.

          Again you never ever want to use non residue cleaner. It can strip away all lubricants and give you a dry pot which then becomes scratchy, wears many times faster and can outright fail.

          If you do have to go all the way in, then you may as well give them all a quick shot. Murphy's law is, when one gets dirty the next is quick to follow. Dint spray the sliders, only the pots. Sliders will tend to go bad even faster and their movement becomes glitchy. Only lubricate slider as a last resort before replacing them. since sliders have that open slot dust gets in there and it sticks to the slider contacts. Its better to use an air can and blow those out and leave then dry.

          Cover your mixer too when not in use. A cloth or towel to cover it will extend its life. Dust is the number one enemy to most mixers pre mature failures pot failure followed by physical abuse. Its just too bad they don't make them more easily replaceable. I do allot of restoration work and allot of this new stuff is so low cost it doesn't pay to repair them. A good tech cost more per hour then what you paid for the thing new in many cases.

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          • #6
            Originally posted by WRGKMC View Post
            Cant see it that well, but you may have to get in there from the top side, and yes that would likely require pulling every knob off the control panel and likely unscrewing all the hex nuts holding the pots to the top panel.
            Those are the mini hex screws to the right of the knobs? Anyone know their size?


            Originally posted by WRGKMC View Post
            The boards may also have some screws to hold them to the top panel too.

            There may be one short cut you can try. It doesn't always work and it can work in 50% of the cases in limited degrees.

            Pull the knob off the trim pot, pull up slightly on the pot shaft and try and force some cleaner down the shaft of the pot from the top.
            You have to work the pot and do this over and over to get enough down the shaft onto the rotary connectors that make contact with the carbon pad.

            Like I said, this is messy so use a paper towel or cloth to surround the pot and catch any extra fluid.

            Lubricating contact has mineral oil in it to lubricate the pots. It will creep too so getting some down that shaft may take a little time to work. you do have to work the pot turning it filly left and right maybe a couple of dozen times. You can usually feel them loosen up as the mineral oil gets in there. Its just hard to know if its getting on the contacts too.
            That sounds like a major hassle. I was planning on giving the entire unit a nice all-over clean/lube.

            Originally posted by WRGKMC View Post
            Again you never ever want to use non residue cleaner. It can strip away all lubricants and give you a dry pot which then becomes scratchy, wears many times faster and can outright fail.
            I use DetoxIt F5 for the pots and D5 for the inputs.

            Originally posted by WRGKMC View Post
            Dint spray the sliders, only the pots. Sliders will tend to go bad even faster and their movement becomes glitchy. Only lubricate slider as a last resort before replacing them. since sliders have that open slot dust gets in there and it sticks to the slider contacts. Its better to use an air can and blow those out and leave then dry.
            There aren't any fader on this unit, just knobs,

            Thanks for all the help,
            -Adam

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            • #7
              I wouldn't have a clue to the screw size. I've refurbished hundreds of mixers but never paid much attention to the actual screw sizes. I have several sets of hex drivers and just grab the one that fits. You can buy a set at an auto parts store that folds up like a pocket knife. you just have to know if its metric or inch. Most newer electronics use metric because they are made overseas.

              DO NOT spray the input jacks if they are the plastic PC mount type. I made the mistake of doing that on a patch bay and every one of the jacks began to crack and fall apart shortly afterwards. The cleaner breaks down the plastic and pops the plastic rivets that hold the metal contacts in place. If you have a bad contact its better to surgically bend the contact out a little with a spring hook to make a better contact. If you have to clean the dirt, put drop of cleaner on your fingers, wipe it on a plug then work it in and out of the plug. Don't just stick the can nozzle in there and squirt. You'll likely regret that decision fro the reasons I mentioned within 6 months or so as the cleaners dry out the plastic and cause it to fail.

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              • #8
                Does DetoxIt make the F100 so it doesn't degrade the parts? Since it's 100% lube, no cleaner?

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                • #9
                  Most contact cleaners use mineral oil, silicones and/or Alcohol.

                  Mineral oil is distilled from Petroleum. Most Plastics is made from petroleum. The two can react with one another.

                  I always view the MSDS sheets on chemicals so I know what's in the product. It saves me from making the kinds of mistakes I've made in the past that had lethal consequences.

                  The F100 lists their chemicals as :"Trade secrets" The manufacturers can get away with this if the chemicals are non toxic and they want to protect their product from being pirated by other companies. F100 is for pots and sliders only. Not connection jacks.

                  As I said, the cleaners seem to break down the plastic in the jacks. It takes awhile. In my case it took a good 6 months before all the plastic around the Nuts cracked and fell apart in pieces. The contacts actually got worse shortly after.

                  This is common in new gear with the plastic PC mount connectors. On old vintage boards with CTS pots and metal Switchcraft connectors, they were made to be serviced and repaired. You could even use Emory cloth on the connectors and clean the contacts to remove oxidation and dirt. If anything did go bad they were easily replaced.

                  That started changing in the later 70's. Tapco started packing their pots with some kind of lubricant we'd call ear wax. Non of the chemicals would remove the stuff very well and if you did get the paste out of the pots they'd be so loose they felt awful. If you used Alcohol based cleaners the stuff would turn into chewing gum and seize the pots up.

                  You commonly find EBay listings for them describing the pots as hard to turn. I've refurbished many of them. you actually have to open the pots and flush them with brake cleaner then repack them with conductive grease. Talk about a nasty job. Half the knobs bust the plastic shafts off the knobs removing them too. They just weren't built to be serviced. they were budge gear you'd get maybe 10 years out of them then throw them on the scrap heap.

                  These new mixers are even worse. I bought a used 12 channel Behringer awhile back. decent board with 4 outs and recorded well enough. I used it for a year and then it sat uncovered for several months. I powered it up and the first volume slider was cutting out. Pushed it over to one side and it would work. I figured it was either dirty or it got bumped and made the casing come loose. The casing is what puts pressure on the contacts and that's what it appeared to be.

                  I did try cleaning it with no results. I actually removed the slider and took it apart. The contact pads had gotten dust on them and it was blocking the contacts. I did get it back together and it works fine now but I put a plastic cover over it now when not in use so I don't have to go through that nightmare again.


                  Here's some other Deoxit info.

                  Deoxit D is for metal contacts only. - Use as a general treatment for connectors, contacts and other metal surfaces, and on non-critical metal surfaces with severe oxidation and corrosion. If the metal surface is discolored, it is severe.

                  DeoxIT® D-Series DN5 - is supposed to be safe on Plastic panels. It mentions nothing about Plastic connectors. It uses Pentafluoropropane that has a 7.5 year residue lifespan, and ISOBUTANE another Petroleum product as a propellant

                  DeoxIT®, #D100S-2 uses something called 1,1-Difluoroethane which is essentially air conditioner refrigerant. It is most likely used to freeze a circuit board fro troubleshooting purposes. I don't know if it actually cleans well but it doesn't leave a residue. No idea how plastic will react with it. Its listed as a metal cleaner only. Dissolves oxidation and corrosion on metal surfaces. Fills in microscopic gaps and reseals surface for better contact to enhance ow of electricity. Chemically improves metal-to-metal connections and contacts.

                  There are other manufacturers who sell non residue cleaners that contain denatured or ethyl type alcohols. These were common cleaners used in electronics, especially switch contacts on older switches that had metal or Bakelite casings. They sometimes work on plastic switches but I'm more likely to open the switch and manually clean the contacts. If they're pitted no cleaner will work and replacement is what's needed.

                  I have found alcohol can dry out some plastics and make them crack, especially any kind of plastics that contain PVC commonly used in connectors. Beyond that, it can also oxidize Lead badly and cause shorts on solder contacts. Again this can take some time, but after spraying electrical contacts, the lead and surrounding areas turn white and conductive.

                  You can wind up causing much more harm then good too.
                  Many boards are sprayed with either a plastic or lacquer sealant to keep moisture and its associated oxidation away from the contacts. I Believe the denatured alcohol in the spray strips the sealant away and accelerates the oxidation. If you've ever seen a board with what looks like dried milk all over the board its because someone sprayed alcohol based cleaners on the board. We used to use Fedron, a nasty petroleum based cleaner on boards. It would clean the contacts and any of the sealant that was last simply liquefies and dries again.

                  Here's a list of the effects of alcohol on plastics.

                  Alcohol will damage some plastics, but not all. I will list my answers by the resin code, or "recycling symbol", found on most plastic items:
                  1. Poly(ethylene terephthalate), PET or PETE - PET is not very soluble in ethanol or isopropanol, but prolonged exposure may cause crazing or stiffening due to dissolution of plasticizers.
                  2. High Density polyethylene, HDPE - HDPE is resistant to most things.
                  3. Poly(vinyl chloride), PVC - PVC is not very soluble in ethanol or isopropanol, but prolonged exposure may cause crazing or stiffening.
                  4. Low Density polyethylene, LDPE - LDPE is resistant to most things.
                  5. Polypropylene, PP - PP is resistant to most things.
                  6. Polystyrene PS - PS is not very soluble in ethanol or isopropanol, but prolonged exposure may cause crazing or stiffening.
                  7. This stands for "other", but the most common is polycarbonate, which is not very soluble in ethanol or isopropanol, but prolonged exposure may cause crazing or stiffening.

                  The connectors may be made of Nylon which is resistant to most chemicals. Most connectors in these mass produced stuff has a percentage of PVC in them which is why I say don't just spray the cleaner into them. If you know exactly what plastics they are then you may be fine.

                  I've been there and done it and my advice is, if its working correctly and you have no issues, leave it the hell alone. Those kinds of connectors as are many pots are one shot deals. If the pots have plastic cases (shafts are ok because they are normally nylon shafts) They wont stay functional after spraying them for more then a few days and the issues will come back twice as bad as they were. The only fix for them is replacement, and replacements are very hard to find and expensive when you start adding up the numbers you may need if you go in there and just randomly spray everything. you may thing its preventative, but can wind up being the end of that piece of gear.

                  The rotary pots are usually OK to spray like I said. I'd only spray the ones that see allot of use and leave the rest alone.
                  Last edited by WRGKMC; 10-07-2015, 03:26 PM.

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                  • #10
                    Oh and the stuff I use for cleaning pots is this.
                    http://www.amazon.com/MG-Chemicals-C.../dp/B008UH3NYU

                    I can buy it locally and it seems to do well on all kinds of Pots. It creeps allot less then mineral oil and attracts less dust so I can go longer without having to redo the pots. I do have one solid state Fender amp from the 80's I cleaned the pots on about 6 years ago. I noticed the pots were a bit scratchy after not using it for a good 6 months or more. I worked the pots good and it went away for the session but I'm likely going to have to clean them again. The pots are real cheap so I's expect this but 5 years between doses was pretty good.

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                    • #11
                      Adam, have you tried to locate an electronics service shop in your area? It's worth a call to ask whether they can look at and service this issue for you. Don't assume every newer device isn't repairable. Some aren't, some are. A good tech can handle even surface-mount devices.
                      Last edited by Craig Vecchione; 10-09-2015, 12:11 PM.
                      "If you don't know where you are going, you might wind up someplace else" - Yogi Berra, 1925-2015

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                      • #12
                        Originally posted by Adam O'Blivion View Post
                        Does anyone know how to get remove this top piece of PCB board and get it out of the way?
                        Get the service manual - it will answer your questions and make your life a lot easier - you will also be able to put the mixer back together when you are done.

                        Mackie 1202 VLZ-PRO Mixer service manual
                        "Isn't it a pity, isn't it a shame,
                        how we break each other's hearts
                        and cause each other pain"

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