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Syncrowave 300 OCV weld problem

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  • Syncrowave 300 OCV weld problem

    So i bought an older syncrowave 300 believe it's a 1989 model about 7 years ago. Ran great for a long time then AC quit. I changed hi freq board and it ran great for the last 4 years no issues. Last week I noticed my shop lights started to flicker which they never did even when running with the hi freq on. They yesterday I lost AC..I have steady flow of high freq at the torch and underneath the machine where the pins are but no ac welding can be done. Even if I set it up just to try and run ac stick.

    Now here is the issue I'm seeing. My voltmeter up on top is only reading 40v OCV with machine at idle(usually runs 80).When I check it with a multimeter it's really at 79 volts and I have 79 volts at the terminals and at the torch, that's with the contactor set to standard and the current set to panel. But it just won't weld on ac. DC it welds but seems like it's only running half the amperage as it should even with the dial turned all the way up. Once and a while for whatever reason the volt meter goes back to 80v where it should be. When I check that with a volt meter it's really at 150v and the machine welds fine even when tig welding alum untill I try to use the high freq. Then it goes back to 40v on the meter and I cant weld ac. Once i mess with it and the ocv meter hits 80 i can weld ac tig If I keep scratch starting I can continue to run the ac. Its weird... I really dont think its the board again because occasionally this thing works its self out...If anyone can help me please throw some knowledge my way. This is killing me. My brain hurts from messing with this today. Thanks in advance
    Last edited by 383welds; 07-30-2020, 11:24 PM.

  • #2
    Update today went back out to the shop fired it up and it has 80v on the ocv meter and it actually is reading 80v with a multimeter where last night once and a while it was reading 80v on the meter but actually 150v. Machine runs fine until I switch on high freq. Then it drops back to 40v and does not weld. But it still has 78v if I check the voltmeter across the two posts in the back

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    • #3
      try stick welding with it if it welds stick you most likely have an open power cable in your tig torch.

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      • #4
        Thanks but like I mentioned in the original post I already tried that. It doesnt weld in ac but DC I get some voltage but not much

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        • #5
          I would check for loose/spotty connections to or from your SCRs. It almost sounds like either one of your SCR diagonals (SCR1 and SCR3 or SCR2 and SCR4) is not firing consistently. The main board fires each diagonal individually through two separate gate drive transformers (FC1,2). I would check the connectors from the board, to those two units, then from those two units to the four SCRs. Then make sure all connections on that SCR output rectifier (4 SCRs and one diode) are tight. I still don't quite yet understand how your OCV was so high, will think about that one some more.

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          • #6
            Thanks for your Input. I have the service manual a d it explains how to test fc1,2 and the scrs so I guess that is next on my list....

            Today I went out and again. I turned it on and volt meter goes right to 80 like it should and I can stick and tig weld aluminum the only catch is I cant use high frequency (even though it works)as soon as I hit the switch from off to start or continuous the machine instantly drops down to 40ocv and won't weld on ac but will weld on dc. But it only gets about 125 amps max on dc. So for now the machine is working but I cant use the high freq.so I have to scratch start everything and trying to scratch start aluminum as we all know sucks.

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            • #7
              Just to feed back to you, AC and DC get correct OCV and amperage consistently unless the HF is firing, whether continuously or in start with contactor on. Sounds like you have narrowed it to interference from the HF circuit. Have you checked continuity on the HF bypass circuits, R11-C13 and C15, C16. There are a couple bypass capacitors on the auxiliary 115V secondary and 24V secondary remote circuit. Also worth checking spark gap.

              It sounds like you're losing one of the diagonals, which would make it very hard to keep the aluminum arc initiated (20ms dead time) and cut your OCV/output in half for DC. Is it having the same impact to your 115V auxiliary winding (CB1 to chassis ground), the 24V AC contactor circuit (pins 24 and 26 on main PC), the 36V AC circuit (pins 2 and 3 on main PC), or the 10V AC timing signal (pin 8 main PC to chassis ground)? If they are also affected, then it is probably something in the HF or bypass circuits. I fixed a guy's Invertec 300 and homemade arc starter circuit (was actually showing similar issues as yours, voltage and amperage dropped way low when HF fired) by bringing the work lead to his homemade arc starter and adding bypass circuits across the electrode and work terminals there. His arc starter kept tripping the wall GFCI until I adjusted the wiring. If those auxiliary circuits are ok, then it may need some board troubleshooting.

              There is a10V AC timing signal off your main transformer (connects to pin 8 on the main board) that is used to time the SCR gate drives. That signal is brought in to pin 8 on the main PC, and connects to two circuits. The first circuit (with IC10), triggers either Q12 or Q13 on, depending on it's polarity. The second circuit starting with IC-8, first integrates that timing signal (shifts the phase 90 degrees) so when the polarity crosses 0, it is at max value (positive or negative depending on which half of the AC cycle) to work as a timing signal. It is then added to some DC voltage (based on pin 6, which is between -15V and 15V based on your balance setting and R78 and R79 ratio). IC9 inverts it, so IC11 and IC12 have positive signals 180 degrees apart, and they differ by two times the bias voltage from pin 6 . IC11 and IC12 compare that timing reference to the negative feedback circuit, which compares the actual current from your hall device amplifier to the reference current signals from the panel/remote input, Pulser unit, and other circuits (IC5). IC11 and IC12, along with Q12 and Q13, tell which gate drive transistor to fire when. Long explanation, but hopefully that may help someone troubleshoot later. With a multimeter, you can troubleshoot by checking continuity/resistance when the circuit is not powered and checking voltages when it is powered. It's worth have the right clips for your multimeter to ensure you're not zapped (secondary circuits are tied to ground) and the board components aren't short circuited. If you use an oscilloscope, just be cautious about the secondary circuits tied to ground, as you could end up with a ground loop that zaps your instruments.

              Hope this helps.
              Jon
              Last edited by jjohn76; 08-02-2020, 02:44 PM.

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              • #8
                Thanks for the reply john sounds like you know a lot about these machines! One thing I did notice which you mentioned was that the machine you fixed would trip the GFCI outlet on the wall,mine also does that sometimes or it will make my shop lights flicker on and off. I've been. Busy with work so I havent been back out there I will let you know when I get a chance to check some of the areas you mentioned. Thanks I really appreciate your help

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                • #9
                  No problem. It certainly sounds like one of your bypass capacitors isn't doing it's job, either broken connection or something.

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                  • #10
                    Originally posted by 383welds View Post
                    One thing I did notice which you mentioned was that the machine you fixed would trip the GFCI outlet on the wall,mine also does that sometimes or it will make my shop lights flicker on and off. I've been. Busy with work so I havent been back out there I will let you know when I get a chance to check some of the areas you mentioned. Thanks I really appreciate your help
                    I don't know whether this is your problem, but I'll throw it out there just in case: I had a similar issue with my ~ 2010 Sync 250. When I started the arc (AC or DC), one or two of the fluorescent fixtures in the shop would either go out, or go from dim to full lighting. This behavior went on for months, but did not seem to affect the welder itself. As time went on, then the GFCI circuit (into which the fluorescent fixtures were plugged) would trip when I started the arc. Eventually I got sick of this, and after someone suggested that maybe the HF from the welder was getting into the coils in the fluorescent light fixtures, and sending a current back to the GFCI causing it to trip, I then replaced several of the older fluorescent fixtures with LEDs. This instantly stopped the problem of the lights either going out, or going from "dim" to "bright" when I lit the arc, and it also stopped the problem of the GFCI tripping.

                    Just something to think about...might be worth a try to see if it solves your welder's misbehavior...good luck.

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                    • #11
                      Originally posted by jjohn76 View Post
                      No problem. It certainly sounds like one of your bypass capacitors isn't doing it's job, either broken connection or something.
                      Thanks for your help. Today after a long break I was digging back into this welder. I found that the high freq intensity knob(device). Has arc marks and is slightly melted. Could this be what is causing this?

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                      • #12
                        So I removed the intensity knob assembly all together and on restart I still only have 36 ocv at the terminals and still have the HF jumping across the points. I broke my continuity tested so I didnt have a chance to check sc1-4 yet either but I will soon. I'm really not good with this type of electrical troubleshooting so please bare with me.

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                        • #13
                          Hi, when you say you removed the intensity knob altogether, did you just connect the two terminals together, or leave them disconnected? It seems like your intensity knob was still conducting because you still had HF/HV at the torch. If there was ever a break in that intensity rheostat winding, it probably arc across until it welded itself back together. It's worth replacing the intensity knob, but you likely have a problem elsewhere. I need to find my 300 manual, can't seem to track it down today...

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                          • #14
                            Originally posted by jjohn76 View Post
                            Hi, when you say you removed the intensity knob altogether, did you just connect the two terminals together, or leave them disconnected? It seems like your intensity knob was still conducting because you still had HF/HV at the torch. If there was ever a break in that intensity rheostat winding, it probably arc across until it welded itself back together. It's worth replacing the intensity knob, but you likely have a problem elsewhere. I need to find my 300 manual, can't seem to track it down today...
                            I just taped the two wires separately and left them dangling while I fired it up. The next chance I get to look into this I'd like to check the scr's and the main diode. Do you know where I can purchase new ones if they happen to be bad??

                            Note*(this is why its driving me crazy).. I did a small ac tig job with the machine this morning. It fired right up and had 80v ocv with HF switched off and I was able to scratch start on the aluminum. Welding at a out 225amps. I was able to finish the job(about 25 minutes weld time) once I got done i decided for the **** of it to see how (if) it would work if I tried switching on the HF. It immediately dropped to 36v ocv and I could weld anything for the rest of the day.

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                            • #15
                              We'll, I will have to think about that one some more. You basically had the HF coupling coil disconnected from the spark gap, so the noise is getting into the timing circuit from somewhere else. How do the other connections with the capacitors and large resistor look like on that HF board?

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