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Help with an old Millermatic 35S

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  • Help with an old Millermatic 35S

    ***EDIT*** Please see post #33 for my update and questions about a speed problem. Thanks.

    Just a little background first. I picked this MM35S up a few weeks ago from a friend. Had no idea of the functional condition as he bought it from Craigslist and never tried it himself.

    I took the panels off, cleaned the years of dirt out of it, replaced a few cables, cleaned and regreased the wire drive gears, cleaned the switches and pots, threw a tank and some
    .035 wire and gave it a whirl.

    Now I am by NO MEANS a welding or welder expert. I learned to weld close to 30 years ago, got decent, then didn’t touch a welder for over 25 years. As a mechanic though and now working at a shop that has a fair amount of rust repair work, I am being called to do some welding. I picked this machine up so I wouldn’t have to deal with the shop welder that gets abused and not maintained.

    So yeah I fired this up and it does weld. But it doesn’t seem to have the penetration it should. Also, it doesn’t sound right. Every other MIG I’ve used has the same snappy, egg frying, bumble bee sound. This one doesn’t. It is a much more subdued hissing type sound. I don’t have any idea if this is normal or not. As for the performance of it, I had it on the highest heat range and it wasn’t going nearly as deep as I would expect. I did check all the diodes (the 4 big ones on the fan unit and rectifier bridge). They all test fine.

    Only other thing I can think of is the 6 big caps. Any way to really test them or am I barking up the wrong tree?

    Last edited by Danimal1969; 08-07-2019, 10:33 AM.

  • #2
    Well Dan, I was recently told I'm a condescending prick so I'm reluctant to offer advice and further degrade my reputation. That said...I'm thinking wrong tree.


    • #3


      • #4
        Hang on, Dan, we can probably help you. Just let the old man complain a little here, then we'll try and work out your issue.


        • #5
          Ok Dan, you have two settings, wire feed speed and voltage. They both impact how your machine welds, but not entirely how you think. You can crank up with voltage, but have the WFS too low and get diddly squat for a weld that makes you sad. So what you need is correct settings for each.

          Let's start with you telling us what you're welding on. How thick and how big. What size wire and what gas you're running. Solid wire or flux core wire. After those are met, we can help dial you in.

          First things to check before we go too far:

          Correct polarity set on your machine.
          Good connections all the way around, including the shielding gas.
          Wire feed welding requires a good ground connection to the work piece.
          Good condition of the contact tip, correct size tip, liner and drive rolls for the wire.

          There, basics covered.

          When you get to practicing, I would swing those dials both to the middle and adjust from there. Only change one thing at a time.

          Keep a short electrical stick out, about a straight in gun angle to start and prep the metal correctly. Grind it down to bright shiny metal.

          See that Noel? Concise info in a readable manner that is not condescending. You should try it.


          • #6
            Thanks for the reply.

            I do realize it’s hard to have any idea if a newbie here has any clue or not. Like I said, I’m no pro but I have had some experience.

            This machine doesn’t have a switch for the amperage/heat range. It has the 6 plugs along the bottom.

            Running .035 solid wire with Ar/Co gas. I had a big chunk of steel, close to an inch thick. I had it on tap #6 and varied the wire speed. Even what I thought was the best looking weld I was able to break the weld bead off with a large cold chisel and 5 pound hammer. Lol. I also used some thick exhaust pipe from a diesel truck and it burnt through that while going a bit too hot. So it’s not like the thing doesn’t work.

            Im off for the weekend and I pulled the liner out tonight before I went home. Gonna order a new one just to be sure that isn’t causing me any issues.

            I appreciate the input.


            • #7
              Ya man, I'm a little familiar with that machine, but not as much as I'd like. Plug that sucker into the middle somewhere to start. Voltage does not necessarily equal penetration, that's controlled more by the WFS. So set it in the middle on each and start from there.

              Does the machine tell you what the voltage setting for each socket is? You should be in the range of 17-18 volts for that thinner stuff.

              Get it set, crank up on the wire feed speed until you feel the wire hitting the base material....that's too fast. Turn it down until the wire starts to kind of surge, it'll burn back a ways then catch up, then burn back a ways and catch up again.....that's too slow. Adjust the WFS until you get a consistent sounding and looking bead that does not crown up or burn through.

              Should be able to adjust a consistent bead on most of those voltage settings.

              Increasing and decreasing amperage is achieved by either using a bigger or smaller wire or by increasing or decreasing the WFS. That's it. Sometimes, and it sounds counter intuitive, but turning up the WFS is what you need to do in order to increase the amps and drive the arc into the weld. Otherwise, it will pile up and look like a big sad caterpillar.

              I salvaged my big old mig machine out from under a redneck's tree where it was sitting for a few years. You can get this thing running right, we can help.


              • #8
                That machine is a sweet little ol lady, not a thug and definitely a girlyman toy with DRO and IPM and crap. It was built by Miller Electric Co, the people who figured out how to weld copper wires to aluminum windings so well those connections have lasted nearly 50 years now.

                She'll weld 3/16 full pen without problems running.035 wire with Co2. Don't need no girlygas on steel, just a man who treats her right.

                Like all elderly ladies she may have a touch of corrosive rumatiz where the copper wires are connected to the plugs. Also gently check the gun plug carefully for being corroded in. If it's stuck a few drops of MMO or PB Blaster and a day or two of soak.


                • #9
                  I'll just add, I'm thinking the 1" thick metal you're welding was absorbing the machines welding heat, the machine is rated for max of 150 amps, you need a big machine to weld 1" metal.

                  I also would use .030 or even .026 solid wire on that machine when welding thinner metals, and you might want to check the where the gas comes out of contact tip adapter, the holes could be plugged somewhat. I run .030 solid wire on my MM 251.

                  Last edited by tackit; 06-22-2019, 06:24 AM.


                  • #10
                    Thanks again for the responses.

                    I forgot to mention, somewhere in this machines life it was retrofitted with a Tweco #2 gun. Good, bad, or indifferent, it’s what I have to work with.

                    Also so I don’t ever plan to be welding metal that thick. I just grabbed that piece from the scrap pile to test the machine. I don’t suspect I’ll be welding much beyond the thickness of an automobile frame. So maybe 1/4”-3/8” at the greatest. It’ll see more duty in the sheetmetal and exhaust area.

                    I was planning to run .030 wire but the parts dept had a roll of .035 so I grabbed that to test it out. I can certainly get some .030 once it’s up and running.

                    Can I just ask what symptoms I might expect to see if my 6 large capacitors are going faulty? This machine is from 1971 and they are original. I know big electrolytic caps are not made to last that long. I’m not anxious to spend money I don’t have to, but I want to make sure it’s running it’s best.


                    • #11
                      You're in the right place. Hopefully Wayne will see this soon and chime in, he's a electronics powerhouse, especially on the good stuff that machine is made from.

                      On my old machine, I hooked my DMM to the power lugs on the lead and work clamp, then worked it to verify the voltage change.

                      So you need to locate the manual for your machine so the smart guys on here can see the right guts if they need to. And post up the machine serial number while you're at it.

                      Our fire shop has that same machine and it's probably about as old as yours. So that machine will have no problem with the demand you're going to put on it.

                      .030 will probably be your best all-round wire for your needs. I use it very little, but I have a dedicated sheet metal machine too. It wears its cover most days, I just don't do a lot of it.


                      • #12
                        The only machine Miller Electric made that was better was the MM-200. The 200 is only better because it has a rotary switch rather than the overly complex system of plugs which many people were too inept to understand.

                        The 35 was designed & built to run .035 wire, and by my recall smaller diameters didn't commonly exist when that machine was made. I assure you the machine has the ability to weld either a tin can up to 3/16 using .035 wire in the hands of a competent weldor using Co2, NOT Girlygas. Remember, when that machine was built, MIG was barely 5 years old in the shop world, and men wore long pants to work.

                        MIG in shops was the beginning of the long road James Lincoln wrote of when he penned the industry needed to develop machines that would eliminate or minimally downsize the need for weldors and replace them with welding machine operators. He probably would have said HotGlue Gun drivers, but hot glue wasn't really in the retail world yet.

                        Changeout of the Miller Electric gun; well the original baseball bat did have a few drawbacks, but it was better than most of the competition and had a 13 foot cable as opposed to 7 foot. The original had a life expectancy of only 36 years although I was able to stretch the life on my MM-200 to 39, and saved the old bustard for an Emergency use gun.

                        Like any machine, it has a personality, and the man using it must learn to work with the machine because the machine ain't going to adjust its electronics to accommodate the operator's shortcomings.

                        If and when the caps go bad you'll have a very nasty arc that will be near impossible to control. Replace all 6 of them at once following Capacitor safety rules, and save yourself some heavy coin by buying them from a capacitor supplier, not a welding supplier.

                        The MM-35 was desupported by the company that bought Miller Electric around 1985! My personal MM-200 was officially desupported around 1990.


                        • #13
                          I officially desupported you and your dadgum Clark bar two days ago.


                          • #14
                            How do ya like them apples?


                            • #15
                              Does your MM35S have the "spot panel"? Probably doesn't matter in relation to your problem, but just a thought/question.

                              As others have said, you have a gem there, and there isn't a lot that can go wrong with it that you can't figure out a fix for.

                              I was very interested in Franz's comment about the bad caps--I have never personally experienced welding with bad caps in a MIG machine; my trusty old MM200 just keeps chuggin' along. (choochin' along, if you're Ryan). I worry about its caps a bit, but I don't fix stuff that ain't broke.

                              Franz's statement makes a lot of sense; a pound of experience beats a ton of "I think"..... I don't know the statistics off hand, but I would guess one of the most common of the six possible failure modes for electrolytic capacitors would be an "open", which simply means it changes from a capacitor to a "nothing" electrically--just an open circuit, no longer providing any filtering. I would expect that to make the arc go wild because the voltage across the arc would become very unstable, which is a bad thing for a constant voltage process. But, I've never experienced it, and it's good to hear someone who has to confirm my suspicions. I would expect the problem to get worse at higher wire speeds.

                              It is possible that your caps have decreased their capacitance due to age and drying out, and are not longer holding the voltage as steady as they should, but I would think in that case, you would be experiencing some degree of wild arc as Franz said. However, another failure mode that is possible is what is called an increase in equivalent series resistance (ESR) of the caps. This is pretty common with old electrolytics; when I am troubleshooting electronic test equipment, first thing I check is ESR of the electrolytics, and often find bad ones. Unfortunately, you need a specialized ESR meter to check for it. If you just check the capacitance value with a standard multimeter that has a capacitance range, it may say it's fine; capacitance can remain at spec with incredibly bad ESR. What I don't know is how increased ESR would affect an arc, but I think it would have some effect. A cap with high ESR still works, but allows a lot of "ripple" to remain on the line it's supposed to be stabilizing. Conjecture says that could cause a change in the sound and quality of the arc, but I have no experience to back that up. I can also see how that might reduce penetration, since the caps aren't providing the "kick" they need to in order to keep the current up. I have some dusty, hazy memory from long ago of reading a post somewhere--maybe Welding Web--about a guy who put new caps in a very old MM200 and it made a world of difference in the arc quality. If you have a multimeter with a capacitance range, it wouldn't hurt to check them with it. May find one that has way low capacitance. If they all show good, it's no guarantee, though. BTW, higher capacitance than the rating is OK--even if it's a lot higher. Just can't go lower.

                              HOWEVER, a set of caps for your machine is going to set you back some bucks, even if you buy them from an electronics supplier instead of a welding parts place, so I would want to know if they're bad before springing for new parts. You need 6--I took a quick look at Mouser distributors; they run from $15-$40 each, depending on quality, and would need to do more research--especially the $15 end feels a bit low priced to me. And for a welder, you need good quality and higher-temp-rated caps than the standard cheapies.

                              Where are you located? Any chance you're close to upstate NY?

                              If you know anyone who does electronics repairs, ask them if they have an ESR meter. Since there are 6 caps in parallel, you will have to take them out and test them one at a time. But get someone who understands the dangers--caps can bite you big time. Check with a known functional DC voltmeter to see if there is a charge on the cap. I used to, and used to recommend, just shorting them with a screwdriver to be sure they're safe, but it seems modern caps can be damaged by the high surge currents that causes; it is now recommended that you put a 5,000 to 10,000 ohm 5 watt resistor to ground from the positive term of the cap, or just jumpered across the cap. Keep it there for about 10 seconds.