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Millermatic Vintage 200wire feed problem

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  • Millermatic Vintage 200wire feed problem

    This welder is serial KK017534, stock no. 903355. We've been using this welder for years with no issues. The other day, the ground for this welder was still clamped to the welding table from work the previous day. The machine was off. I needed to do some stick welding and we use a Dialarc 250 for that. I clamped the Dialarc ground to the table, switched on the Dialarc power, and within seconds, smoke started pouring from the Millermatic Vintage. I yanked the plug out of the socket immediately, turned off the Dialarc, and opened up the case on the wire feed. I found several leaking capacitors. I asked around a bit, got a suggestion that maybe a diode was bad, so I ordered new diodes and new capacitors. I installed these parts, turned on the welder, Everything seemed good at first. Then when I started feeding the wire back through to the gun, within seconds it smoked more capacitors. I'm looking for an idea what is wrong with this machine. I'd love to fix it, because it has really worked well up until now. Anyone got any experience with this sort of issue?

  • #2
    I've never heard of this being an issue. Large weldments often have work leads from several machines (on and off) clamped on at the same time.

    What is the condition of the DialArc? Could it be what started it?
    Last edited by MAC702; 04-16-2020, 03:33 PM.

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    • #3
      The Dialarc works great. I used it several hours today. I'm sure I've stick welded on the table when another guy was using the MIG multiple times before. I don't know what to think myself. I talked to a guy who used to do welder repair and he said it could just be a coincidence since the wire feed wasn't on.. But I don't think it was. I'm just not sure what to think. Or what could be wrong with the wire feed now.

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      • #4
        What is the power input to both the Dialarc and the Mig? Are they fed from a common panel? Have you ever connected their work leads together before? About the only thing that can blow capacitors that quickly is a huge ac voltage across them, or DC voltage far above their rating. I'm betting on some wiring mixup somewhere, although off the top of my head I can't come up with a scenario. Start by checking the continuity of the earth ground pins on the power plugs to the chassis of both welders. Then check the ground pins of the outlets you have them plugged into, back to the breaker box and be sure the earth ground wire from the breaker box has not come loose from the ground rod/water pipe/whatever your electrical system uses for a ground. I would like to think a breaker should have tripped somewhere, but obviously that didn't happen. Specifically, what capacitors in the machine got toasted?

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        • #5
          Could it be a ground loop because somewhere the common was used for a ground?

          ---Meltedmetal
          ---Meltedmetal

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          • #6
            Originally posted by Meltedmetal View Post
            Could it be a ground loop because somewhere the common was used for a ground?

            ---Meltedmetal
            Agree--my thought, too, although I haven't sat down and tried to figure out the exact way it would cause the problem. I'm thinking if all the equipment grounding conductors were properly connected, and the primary wiring were correct, it couldn't happen. It would seem there is no other path except back through the power feeds somehow.

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            • #7
              It may be worth checking continuity from your ground clamp to all three blades on your plug for both machines. None of them should have continuity.

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              • #8
                I will check grounds but both these machines have been in use in the shop for over 10 years now. They get power from the same panel. Hard to believe this issue just showed up from miswiring after being wired the same way for over 10 years.

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                • #9
                  He didn't say it was miswired. A fault can develop from a broken component inside.

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                  • #10
                    Check both machines thoroughly, not only with your ohmmeter but also by looking at everything inside in detail with a good strong light. Things do occasionally come loose and move around inside equipment, or insulation rubs off where a cable has been vibrating against a sharp edge, etc. Sometimes it's not real obvious. Resulting problems are certainly not unheard of--I've found some pretty frightening and/or hard to isolate problems inside equipment and electrical systems that I certainly never expected. I think anyone who has spent some time in the electrical/electronic trades or businesses has stories. And there are updates to the National Electrical Code every three years, often driven by things (sometimes resulting in deaths) that no one thought would happen. Gotta be careful with stuff that can kill you--or toast your expensive equipment.

                    EDIT: Mac had the same thoughts while I was typing.

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                    • #11
                      The pics shows the capacitors that are getting smoked. They get smoked now when I depress the trigger on the gun to start wire feed/output power. Until output power is engaged, capacitors are safe. I'm still checking wiring/connections but so far nothing amiss there.

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                      • #12
                        Wow--at the price of those capacitors, this can get pretty expensive pretty quickly. There are only three things that are going to toast those capacitors quickly--putting AC voltage on them, hooking them up in the circuit with the polarity reversed, or putting DC voltage on them higher than their rated voltage. Has to be one of those three. Too-high DC voltage seems like a stretch unless you have a short in the transformer between primary and secondary. Possible, but certainly unlikely. If the voltage got that high, it would expect it to blow the (new) diodes, which could result in them passing AC to the caps if they fail shorted.

                        You can check the transformer with an ohmmeter. Put one of the leads on one of the wires on the power line side of the transformer, and one on either of the secondary leads going to the diodes. There should be no continuity. Seems if there's a short there, the breaker would have tripped, but stranger things have happened.

                        If that is OK, put a DC voltmeter on the capacitors and be sure the + side has positive volts and the - side has negative. You could check the diodes again and see if they are blown. My first thought is there could be a short circuit somewhere that is allowing AC to bypass the diodes and hit the capacitors.

                        Do you know anyone that has an oscilloscope? I would love to know what the voltage on those capacitors looks like. Where are you located?

                        CAUTION: Stay on the other side of the machine from the caps, and wear safety glasses as well as a full face shield while you're doing the voltage checks, and don't leave the machine on very long. If those caps have AC on them, the explosion that occurs when they finally give up completely can be spectacular, especially with caps that large. Wet paper and aluminum shrapnel flying everywhere. That's not supposed to happen--the vent holes are supposed to release the pressure before they blow--but I have seen it and it isn't pretty. And it will scare the pants off of you!

                        As a general rule, some sort of eye protection is always appropriate, even on low-power circuits. I have seen the tops blow off of integrated circuits with chunks of plastic flying hard enough to cut a guy's face. Faces heal; eyes not so much.
                        Last edited by Aeronca41; 04-20-2020, 08:38 AM.

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                        • #13
                          Aeronca41, after reading your response, I went back through things in the machine again with more checks. I decided that the best way to protect blowing capacitors while powered up was to disconnect one of the leads from the bank and take them out of the equation. I removed the cable and turned on the power. No smoke or sparks anywhere so good. I depressed the trigger on the gun and fed some wire. Still good, I checked for output power. Output power seemed good. So I checked voltage between the capacitor input cable and the bank. Then I reversed the leads and checked voltage. Different voltage reading. At this point I decided to call Miller tech support since my local Miller repair guy said he had no idea what to tell me to check. I got a very knowledgeable guy at Miller today. I told him how the problem started, what I had replaced so far, and the problem I was still having. He said the original problem probably came from a bad diode. And he told me that it sounded like the current problem might be due to installing one of the new caps with the polarity reversed. I said, ok, I can check that pretty easily. I pulled out the capacitor bank, put it on the table where I could see, and started pulling them one by one. Sure enough, I had one reversed. I put in one of the older ones that tested ok and re-intstalled the bank. I plugged the machine in and turned on the power. Good. I pressed the trigger and fed some wire. Good. I clamped the ground to a piece of steel, turned on the gas, and pressed the trigger. The old girl welded like she always has. I'm very happy that I get to use the old workhorse a while longer! Thanks for the help guys. And thanks Miller for having good techs on staff!!!

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                          • #14
                            Fantastic! And it didn't cost another dime!

                            I always say the only people that don't make mistakes are those that don't do anything, and hooking a cap up backwards is not an uncommon error. I have to say I've done it. Fixing a power supply in a church organ many years ago. Just a moment of lack of attention and BANG! when I turned on the power. Fortunately, it was a small one, and was pointed away from me, but still loud enough to scare me.

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                            • #15
                              I'm very happy that it was a simple error that was keeping my machine from working. I've been using it for years, I'm used to it, I've got consumables on hand, and I bought it from a really nice guy who is now in welder's heaven (he passed on several years ago). I learned to weld years ago and spent quite a bit of time welding with an old Miller Dialarc in my uncle's shop 25 years ago. I know the new inverter-based machines are more energy efficient and have more features (and I have those machines too) but I love my old transformer-based machines like they were children. We use an old 330 A/BP for TIG welding virtually every day. I've been into the workings of that several times over the years. The old Dialarc 250 has never given a minute's trouble, and now the Millermatic Vintage is back to top condition. I've rebrushed and refurbed our Bobcat 225 several times over the years and it still works great. I looked inside the Dynasty one time as well as our Maxstar and I know when they act up, it's going to be a challenge!

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