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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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