Syncrowave 351 AC issues
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  1. #1

    Syncrowave 351 AC issues

    I picked up this Miller Syncrowave 351 for free and figured I would try and get it up and running. I found it on Craigslist as: "free welder and tank". I went to pick it up thinking I'd score an extra cylinder and a junk welder. No real discription or picture. Turns out the tank was an large old oil tank and that the welder was the intresting find. I needed a unit that could do AC GTAW for aluminum and figured with a bit of love this unit might do it for me. The only background I have on it was it was sold at a government auction and the person that bought it never even hooked it up.

    I got it home, cleared out all the dust, checked the internals didn't look damaged or burnt smelling. There is some rust on mainly on the bottom of the unit. I also cleaned and set the HF spark gaps. I wired it up to my 50 amp 230v circuit figuring it was enough to test it and I'll wire it up to a 100 amp once she's running well.

    I put some leads on it and tested DCEP SMAW and she welded just fine. A bit of a hum sound, but I figured that was normal for this beast.

    Here is where I need some guidance. I tried powering off the unit and rigged up a tig torch, flipped it to AC and powered it back up. All looked good so far.. till I flip the switch for GTAW and the unit trips the breaker. I tried powering it up with the unit on GTAW and it powers up, but the Amp reading is 0. No pedal, unit is set on panel control and HF turned off.

    I need someone to point me towards a good reasource on what parts to test and how to do it. I have a lead on another 351, with a bad gas relay, I could get for parts if something major is blown.

    Syncrowave 351
    Serial number: JK150062
    No optional, pulser, spot time etc

    Thanks in advance,
    Jeff

  2. #2
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,267

    Re: Syncrowave 351 AC issues

    Find the main diode SCR assembly in the middle of the welder. Test all the diodes for a short.
    If i remember correctly, the is a large diode across the SCR assembly that is only in the circuit in AC
    If it is shorted, it acts like what you describe. You can get the owners and parts manual from miller web site.
    You can call Miller tech support and they might point you in the right direction.
    Make sure welder is unplugged when testing, remove leads from weld terminals. If a short is found you will need to open connections and isolate diode. make sure to mark wires so you know where they go later.
    The one i am thinking of is hard to get to and partly covered in nomex tubing.

  3. #3
    Join Date
    Jun 2012
    Location
    CT
    Posts
    2,715

    Re: Syncrowave 351 AC issues

    yeah, but I don't think the SCRs could be bad if it welds OK on DC. Might be a main board, but hard to tell when it isn't hooked up to a properly sized circuit. I just pulled down the schematic and I couldn't see anything in the circuit that was only on the AC side. What does it do if you TIG weld in DC?
    Hobart Handler 190
    Syncrowave 250
    Purox Metalmaster

  4. #4
    Join Date
    Apr 2017
    Posts
    320

    Re: Syncrowave 351 AC issues

    So I understand you correctly ,your primary power braker trips when the machine is set on AC-GTAW high freq start, but will work fine in DC SMAW.
    You stated that you set the arc gaps, did you set for .0008 gap? If they touch with a lower then required braker they can trip. ( shorts the transformer)
    Did the tig torch you were using could have grounded out in any way?
    If it only trips in GTAW-AC with High Freq on the circuit is simple , the high freq transformer is powered off PC-3 relay board and that is controlled through PC-2 filter board and on to PC-1 main board.
    There is really no reason it should trip just because the high freq was switched on, its a very low input voltage that feeds the step up transformer for high freq.
    Will it GTAW in DC with HF start?

  5. #5
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,267

    Re: Syncrowave 351 AC issues

    SCRs should be OK. I was thinking of a large diode that is switched in and out when going from AC to DC.
    But the 351 doesn't have it. don't have a 351 in the shop right now to look at.
    SO after looking at a couple of diagrams, if it welds ok in DC but trips the wall breaker in AC.
    You need to look at the mode switch blades real close. One may not be moving when you change from DC to AC.
    other wise you will need to look for something that can cause a short in AC and is switched out when the welder is in DC.

  6. #6
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,267

    Re: Syncrowave 351 AC issues

    If the other 351 has a serial number KGxxxxxx or older. the gas valve problem might be C18 on the filter pcb.
    Disk cap that has a insulation break down. Or it is a relay on the relay pcb.
    I work on a lot of machines and they blend together some times.

  7. #7

    Re: Syncrowave 351 AC issues

    First off, Thanks everyone for the replies.

    I did set the HF points to around .0008, however I do have the HF turned off at the panel. The points had a little rust on them and I lightly cleaned them up. I'll replace them a little later down the road of this repair.

    The Tig torch if fairly new and I used it a few weeks ago without issue.

    I'll check to see how GTAW-DC goes and try with and without HF.

    I haven't tested Diodes before, but I'm sure a quick Google search will get me started.

    The blade theory may be on to something as there was some minor damage to the top of the selector area. I'll check that out as well and report on all the results.

  8. #8

    Re: Syncrowave 351 AC issues

    I was at the shop with my daughter working on other project and had a few mins to tinker with this machine.

    I tried GTAW-DC with the panel set to SMAW it works great, when I flip it to GTAW it makes a solid arc, however when I break the arc the machine's amp readings goto zero. I'm scratch starting GTAW as I haven't picked up a pedal yet. I'm assuming I can't try HF till I do? I did try flipping the HF switch to start and continuous in GTAW-DC, but didn't notice any changes. I'm running gas directly to my torch, I need to grab some more gas hose to rig it up through the machine.

    The blades all seem to be turning as they should, none seem stuck.

    I did notice that a one point while flipping the panel switch for HF from off to start, and this may be coensidence, but the loud hum noise went from Loud to more of dull hum (about how I think it should sound at idle). It came back after shutting the unit on and off and I couldn't replicate it. The sound seems to be coming from the black box on the bottom right that the on switch wire goes to. Also if the on button isn't pressed down firmly and quickly the unit will trip the breaker.

    I haven't ever seen the fans kick in. Im assuming they will once the machine gets hot. I haven't done any real welding with the machine just some quick practice beads in the sub 100 amp range.

    I'll pickup a pedal, some gas hoses and some new HF points and keep testing. I'll start checking out the diodes when I have some time to start pulling the machine part. Is that loud hum normal from the black box? If not can it be repaired or do i just replace the whole thing. I Manual calls it a contactor, part number: 187 416.

  9. #9
    Join Date
    Apr 2017
    Posts
    320

    Re: Syncrowave 351 AC issues

    Just for giggles are the jumper links in this machine linked for your primary voltage ?
    The contactor buzzing could be a number of things there a little noisy with age and that's ok most of the time. Other problems could be contacts, coil or incorrect coil voltage.
    It is not all that surprising to me that the machine trips your braker, if your only running a 50 amp and if its tripped a few times the bi-metal inside the braker can break down through heating allowing a trip at a lower amperage.
    To get this guy up and going your going to have to supply something a little closer to its rated primary input power, maybe not the full required but close.
    You can run HF continuously for applications such as aluminum GTAW and HF start only for carbon steel etc, without a foot pedal, give it a try.
    So far what I am reading in your post is that the machine works or am I missing something?
    You may want to hold on the HF arc points for now as there probably isn't anything wrong with them and you stated there at correct adjustment.
    Before I would do much pulling apart I would check the jumpers and see about some decent input amperage.....

  10. #10
    Join Date
    Feb 2014
    Location
    kornfield kounty IA
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    445

    Re: Syncrowave 351 AC issues

    I think the factory manual says .012 gap. .0008 is way small.

  11. #11
    Join Date
    Apr 2017
    Posts
    320

    Re: Syncrowave 351 AC issues

    Quote Originally Posted by gundog77 View Post
    I think the factory manual says .012 gap. .0008 is way small.
    No, all Syncrowave 351's normal arc gap is .0008

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