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Synchrowave 350LX Problem-Help!

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  • Synchrowave 350LX Problem-Help!

    My SW350LX (S/N:LF046890) was working fine. When I turned the power switch off, I heard a noise behind the control panel. I turned it back on and the foot pedal won’t start an arc or start the gas flow nor does the fan come on. In “Lift Arc”, I get a small, unsustainable, arc. In the “On” mode, the fan comes on and gas flows continuously. When I turn it on in DCEN, the volt and amp display sequence is: (V: “209”, A: “882”), (V: “-4”, A: “ “), & finally (V: “- - -“, A: “164”).

    Aid from the Miller TIG Service Group determined the foot pedal was not the problem.

    I have the mother board out and don’t see any visible/obvious signs of component failure on the board or elsewhere.

    I had a similar problem 8 years ago; the foot pedal stop working without notice between beads. It turned out to be either diode D41 or D42 on the motherboard. I don’t recall which one it was but I replaced both. I don’t believe they’re the problem this time.

    Does anyone have any suggestions/recommendations that I can pursue to solve this problem? Does anyone have a schematic for the entire machine (more than what’s presented in the owners manual)? I’m trying to avoid sending the machine in for repair because that would easily exceed the value of the machine which would force me to scrap it. That’s especially difficult to accept when I know it’s some component that I could replace myself; I just don’t know which one it is.

  • #2
    My machine has the PFC (Power Factor Correction) option. I’ve discovered one of the capacitors is completely dead. The capacitor is:

    ASC Capacitors
    X386S(M020), 200MFD +/- 10%, 250VAC.

    I called ASC Capacitors and learned the “(M020)” is their in-house designation for this custom designed capacitor for Miller. I also learned this is a “Run Capacitor.” They don’t have any in stock and haven’t for years. Further, my request for 3 ea. (I already replaced one of the four in 2014) doesn’t meet their minimum custom build lot quantity. Even if it did, their lead time for it would be one year!

    I called the Miller TIG Service Group and they also don’t have any in stock and haven’t for years. They told me their part number for this capacitor is: 203517 and it’s 150 MFD. They show nothing for 200 MFD. They felt a previous owner changed it to the higher capacitance. I know the previous owner and don’t believe this happened.

    Googling I find 200MFD, 250VAC capacitors but they’re “Start Capacitors” and as such have a high side tolerance range associated with them. To the best of my knowledge, they are not as robust as Run Capacitors.

    Does anyone know where I can get new-old stock, correct ASC capacitors or some other brand that’s: 200MFD +/-10%, 250VAC, Run Capacitor?

    Does anyone have the Miller 203517, 150 MFD in their machine? Does anyone know if the 150 MFD will damage my machine that has the 200 MFD? Does anyone have any suggestions; where to from here?


    • #3
      Is this a different problem than the first post? What's your current breaker for the welder circuit? You will definitely need run caps instead of start caps if you want to keep the PFC option. Just remember, the PFC caps are an option. They are in parallel with the primary of the transformer to balance out the inductance of the transformer, so you get less reactive current at higher current outputs, so you can run the higher current on a smaller breaker and wiring. But they are not necessary. Having less capacitance in your PFC caps won't damage your machine, but it may limit your max output current and/or balance on the current circuit/breaker. You could get away with only 3 PFC caps in your welder, though you may not get the peak 450 amps or whatever that machine pushes without a 100+ circuit.


      • #4
        This dead capacitor I’m hoping is the cause of the problem in my first post.

        With the 200MFD setup, I’m running my machine on a 220 VAC, 90 amp breaker. I like it that way because my entire shop has a 220 VAC, 100 amp breaker. To troubleshoot, I thought of disconnecting all four capacitors and trying a low amp output just to see if it will work but fear of damaging the machine. I don’t know if it’s somehow programmed for the PFC option. From what you’re saying though, it sounds like the capacitor isn’t the problem. I checked all the capacitors and resistors I could reach and only found the PFC capacitor dead. I was encouraged because the muffled pop I heard when I flipped the On/Off switch to Off seemed like it came from the approximate location of the PFC capacitor bank. In addition, the ends of the bad capacitor are bulging. Is it possible an imbalance in the inductance on one leg of the transformer primary causes problems for the motherboard?


        • #5
          Hi Puddles, hopefully you received my PM. I wouldn't have any issue testing with the PFC capacitors (or just the one) pulled from the machine, but would advise discussing with the Miller Tech Support if you're concerned.

          A failed cap would likely show a short to the primary and pop your circuit breaker. A bulged cap needs replacing or removal at the least - when you say it's dead, how did you measure to confirm? All legs and pfc capacitors banks look like they're connected in parallel, so I don't think you would see an imbalance.

          I need to dig a little deeper at the tech manual (only looked at PT375s with the lift Arc). Are you able to measure or see any voltage on the panel when you're set to Continuous? ​​​​​​


          • #6
            Puddles, I'd add that 800uF seems like a lot of capacitance to have for PFC in that welder. That makes for ~75A reactive current at idle. The 600uF (4x150uF) would be closer to the ~50A reactive current at idle I have seen in other 300-350 class machines. I have run 300 class machines on a 30A breaker by removing 2/3 the capacitance. Matter of fact, I think the PFC on an Aircrafter 330ST I repaired a long time ago had 3x200 amp PFC caps.


            • #7
              Thank you for your two follow up messages. My apologies for not responding sooner. I didn’t receive your private email message. Not in my Inbox or Junk. Please try again.

              To test the PFC caps, I disconnected the wires from each one in turn and used my Fluke VOM which has a capacitor test selection. The other 3 caps measured 200 MFD +/-10%. The bad one measures zero.

              As I mentioned before, I was able to replace one of the 200’s in 2014 but today no one has stock in them. So what I’m investigating is getting an ASC X386S (M020) 150 MFD, +/-10%,250 VAC, RUN cap plus a compatible 50 MFD cap in parallel for troubleshooting purposes. If this fixes the problem, I might run with that until one of the two remaining 200’s fail then convert to 4ea. X 150 MFD all together.

              At present, my machine is inoperative. I don’t recall what the V & A screens said on Continuous. I had to put the covers back on to protect it from dust from other work in the shop. If an important diagnostic can be learned, I’ll be happy to take the covers off, put the bad cap back in, and test it. In doing so, what will that tell us?


              • #8
                He probably sent you a message through the forum's message system... there should be a button at the very top right of the page to see them.


                • #9
                  Output board is likely the culprit here, not fixable, requires replacement.


                  • #10
                    Thank you for your response. Unfortunately, I don’t know what the “Output board” is. I assume you’re not referring to PC1, which have referred to as the “motherboard,” because I’ve found a few places that will repair them. Would you please describe the Output Board further so I can identify it. I don’t see anything labeled as such on the schematics in the Technical Manual (TM-363E) that I have.
                    Thank you


                    • #11
                      Control board PC1


                      • #12
                        Weld dr,
                        I was afraid it might be PC1. A new board exceeds the value of the machine. The Tech Manual tells what measurements one should read on each pin in each receptacle on PC1. That’s great information but it doesn’t present any procedural instructions to make those measurements. Can anyone direct me to those instructions or can tell me how to do it?


                        • #13
                          I want to thank everyone for all of their suggestions and assistance with this problem.

                          I would like to summarize all of the forgoing to tie the symptoms, troubleshooting, and repair into a single concise posting.

                          In 2014 my Synchrowave 350LX (S/N: LF046890) simply quit working between beads. I stepped on the pedal and nothing happened; no arc or gas flow. I found diode D42 on PC1 had failed and one of the PFC capacitors was leaking. I replaced both D41, D42, and the capacitor.

                          This year, 2022, I had a similar problem. While shutting my machine off, my finger slipped on the switch. It wasn’t a single clean toggle of the switch handle. I heard a muffled “pop” down low on the right side of the machine (where the PFC capacitors are located). Concerned, I turned it back on and found no arc or gas flow. I noted the similarity of the symptoms to 2014 but felt D41 & D42 were new enough they shouldn’t be the problem.

                          After considerable study of schematics and troubleshooting, I discovered diode D42 failed again and a PFC capacitor (connected in parallel to the first one) had also failed. D42 had become a direct short to frame ground for the +15 VDC voltage measured on pin A in the 14 pin foot pedal receptacle located on the front of the machine. It’s suspicious, it failed in 2014 and one of the PFC capacitors was bad then as well. It’s the same scenario now but I don’t know if the capacitor and diode failures are related or just coincidence. I removed PC1 and replaced D42 and replaced the faulty capacitor as well. I’m back up and running.

                          Per Miller in 2014, D42=D41= “Vishay Semiconductor P/N: P6KE30A-E3/54” on PC1. On my machine, PC1 is Miller P/N: 209877C but has been superseded by Miller P/N: 237587. I don’t know anything about D41 or D42 on 237587.

                          Thanks again to everyone. I hope this helps another Synchrowave user.


                          • #14
                            Thanks for the post! Too many people just vanish and don't post solutions for other people to benefit from.