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Synchrowave 350 from 1992 - OFF button won't power it off.

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  • Synchrowave 350 from 1992 - OFF button won't power it off.

    I own a Synchrowave 350 from 1992 that is full dress, including the programmer. Recently the OFF button has stopped working. The only way to shut it down is to cycle the circuit breaker off and on. I ordered the machine with the Power Factor Correction option, causing it to idle at about 40 amps of 240 current draw. Back in '92, Miller advised me how do disconnect the Power Factor Correction option's capacitor bank - the only time I ever went inside the covers. Has anyone ever had the won't power off problem, and if so, how did you correct it?

  • #2
    Post your serial number and I'll take a look at the schematic and see if we can figure it out.


    • #3
      Originally posted by Aeronca41 View Post
      Post your serial number and I'll take a look at the schematic and see if we can figure it out.
      The Synchrowave 350 S/N is KA782001. Click image for larger version  Name:	Synchrowave 350 ON-OFF Figure 10-8.jpg Views:	88 Size:	24.5 KB ID:	601501

      The Power ON/OFF switch feels heavy, mechanical and spring-loaded, not your average momentary contact ON/OFF switch. The parts explosion in the manual shows a mechanical cable, like on a bicycle brake (not a conductor), going into the back section of the machine. I can't tell from the parts diagram figure 10-8 which is ON and OFF.
      Last edited by jpcallan; 09-08-2019, 04:12 AM.


      • #4
        Reminds me of why the door panel is off my 99 GMC. Bloody cable broken on the window motor. Sounds like one way or another the cover is coming off? Question is , is it the cable or something else? Item #26 page 40.


        • #5
          92 might be a bit difficult since it's a Genuine Miller Electric machine made the year before Nels heirs sold the company.


          • #6
            Not being able to look at the machine, I'm guessing at how the ON switch works, and my guess from looking at the diagrams is consistent with your description of a heavy, spring-loaded mechanical feel. This is a lot of conjecture on my part, but I think it's reasonably close to how it must work. I have pasted together the portion of the schematic diagram that shows the on/off functions, along with the mechanical picture of the front panel switches from the manual. There is a contactor (relay) labeled "W" that when energized turns on the welder. We will talk about how it gets turned on in a minute, but your problem is getting it turned off. The red arrow below points to a switch labeled "POWER OFF" on the schematic. This is a small microswitch, shown as item 5 at the other end of the red line on the mechanical diagram. Relay coil "W", an electromagnet, is located just above this switch on the schematic, above the diode--it is the circle with the W in it. As soon as power comes from the wall box, through the transformer, the relay gets energized (as I said, -more on that in a minute) by current flowing from the transformer secondary winding, through the POWER OFF switch (whose contacts are closed, completing the circuit), through the diode, through W, and back to the transformer. To turn off the welder, you push the OFF button, Item 1 on the mechanical diagram, which is supposed to mechanically hit the moveable arm on the OFF switch, Item 5, which breaks the circuit and causes the relay to demagnetize and drop out, turning off the welder. Either that little switch has gone bad and is not opening, or there is a problem causing the OFF button to mechanically not connect with the switch. This should be a pretty easy fix, especially if it's just a mechanical issue. It it's the switch itself, that's also easy if you can find the exact switch to replace it. If not, there are plenty of options we can work through--this does not appear to be a hard problem.

            So, be sure the power is off at the wall box, open up the machine, look for this little switch behind the control panel, and see if it is actuating when you push the stop button. Do you have and know how to use an ohmmeter to check the switch action? If not, post and ask....will lead you through it. The circuit design uses the NC (Normally closed) contacts of the switch; that is, unless you push it, it is "on". There has to be a mechanical issue either with the button or the switch actuating arm, or the switch itself is stuck "on" internally.

            Now, about how the welder gets turned on, and why the ON button feels kinda klunky--I can't say for sure without looking at the machine itself, but it appears to me that when you push the "ON" button (Item 3 on the mechanical diagram), that long rod must physically push the contactor arm of the relay W to the energized/magnetized/ON (whatever you want to call it) position. This is a bit of an unorthodox approach, since relays are generally actuated electrically, but there is absolutely no reason this won't work effectively, using less parts than the normal way. Kind of ingenious, actually. The area where I have drawn the red ellipse on the schematic shows the electrical contacts from the W relay/contactor, and the schematic has the ON label drawn near the contacts. So, when you push the ON button, the relay contacts in the red ellipse are closed because you have mechanically moved the relay to the "ON" position, power from the wall hits the transformer, the transformer secondary winding over by the W relay's coil goes hot, and as long as the OFF button isn't pushed, the relay will stay energized until power from the wall is lost, or the OFF button is pushed to break the circuit.

            Have a look, and let us all know what you find in there.

            Click image for larger version  Name:	SYNC_350_ON_OFF.jpg Views:	0 Size:	46.7 KB ID:	601516
            Attached Files
            Last edited by Aeronca41; 09-01-2019, 10:27 PM. Reason: Clarify first paragraph.


            • #7
              Thank you for the thorough research.

              I have a 4-torch selector box and the SP-34 Programmer on top of the Synchrowave 350. The wife has agreed to help me move all that and other miscellaneous stuff (that shouldn't be on top of the unit in the first place) on Labor Day before it gets too hot in the garage.

              My bet is the tiny bolt that holds the #5 microswitch to the bracket have vibrated loose over the years from trembling caused by the huge cooling fan. We will see on Monday morning...,


              • #8
                Sounds like a good plan, and if you're right about the loose switch, you should have it fixed in no time once you get to it. Add a little blue Loctite to the mounting bolt if that's it.


                • #9
                  I’m going with a 62.74% chance that’s the problem. Now if it was my would be a zero % chance it would be that easy, and that would be an optimistic forecast....good thing it’s not my machine, we’d be elbows deep in this thing for days, maybe even weeks.


                  • #10
                    Originally posted by ryanjones2150 View Post
                    I’m going with a 62.74% chance that’s the problem. Now if it was my would be a zero % chance it would be that easy, and that would be an optimistic forecast....good thing it’s not my machine, we’d be elbows deep in this thing for days, maybe even weeks.
                    ...Gotta be an easy one once in a while! Hope it's this one.


                    • #11
                      I forgot I had an outpatient test at the hospital, so work on the Synchrowave has to be put off for a day or two. I promise to post the cause and, with a little luck, include a photo.


                      • #12
                        Good luck! Anxious to see what you find.


                        • #13
                          Problem cause found, but not what I suspected. The OFF microswitch, Miller P/N 027878, was the cause, but strangely not because it was loose or unscrewed. The switch has a red rubber diaphragm around its plastic on/off button; the rubber had gotten so hard with age as to completely restrict the movement of the button, causing the metal arm to bend instead. See photos.

                          First is switch removed. Note rubber diaphragm residue around yellow button.
                          Second photo is OFF switch in place with one lead removed to allow continuity and switch operation testing with an ohmmeter.

                          Click image for larger version  Name:	Syncrowave 350 P-N 027878 OFF Microswitch 3.jpg Views:	0 Size:	31.3 KB ID:	601651Click image for larger version  Name:	Syncrowave 350 P-N 027878 OFF Microswitch 2.jpg Views:	0 Size:	62.3 KB ID:	601652

                          I assume this rubber diaphragm is intended to keep airborne dust and grit out of the switch internals. The Miller replacement 027878 part is $45. Got to love those ITW prices! My fix is to remove the hardened rubber with a pick and tweezers. The left photo shows the switch after removing the unwanted rubber. The modified switch works great again, and I'm back in business.

                          Thank you to all that chimed in with the helpful insights and research work. I'm in your debt.


                          • #14
                            I’ll be expecting payment within 30 days or the prices doubles.


                            • #15
                              Great (and really cheap) find and fix! Miller4less discounts that switch--It's only 31 bucks on their site!

                              Another case of a very low-tech issue causing a failure; seen several of them over the years. I'll bet the reliability engineer who did the MTBF prediction on that switch when it was designed never thought of this issue. If someone had brought that up in a discussion back when I was doing reliability engineering, the rest of the group would probably have spontaneously thrown erasers and paperclips at him!

                              I will digress with a small hijack on that topic. Ever heard of Admiral Grace Hopper? She was an absolutely amazing lady. The inventor of COBOL, (COmmon Business-Oriented Language). I believe she was the first to make it possible for people who did not understand native computer machine language to program a computer in a higher-level language, and was generally a pioneer in much of what we take for granted in the computer field today. There is a lot of argument and disagreement on whether she actually "invented" the term "bug" to describe a computer problem (I don't think she did, and her log entry sort of seems to assume the word was already in use), but you can go to the Smithsonian today and see her log entry with a moth that had gotten stuck in a relay in the computer she was working on taped to the page . Her entry reads, "First actual case of bug being found." This link is an interesting read, even if the guy who did the file structure spelled her name Hooper rather than Hopper.


                              Glad you found your problem, and it was so easy to solve! BTW, your machine looks really nice and clean inside for it's age.

                              Just in case that switch fails again, or someone else looks at this thread later, here is a link to the manufacturer catalog--that vendor part number BZ-2RC55512 is apparently obsolete, but I'm sure one of the BZ-2RW-- series would work. Just have to look at the mechanical diagrams and find one with the same dimensions that meets the electrical requirements. It was designed to be waterproof; I'm sure Miller was more worried about grinding dust than water when they chose a sealed switch for that application.


                              ...and be sure to send Ryan his fee!
                              Last edited by Aeronca41; 09-05-2019, 09:07 AM. Reason: Added Ryan's fee statement.