Announcement

Collapse
No announcement yet.

sycrowave 300 wont weld in ac but works in dc

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • sycrowave 300 wont weld in ac but works in dc

    I have a 1983 sycrowave 300 that works in dc while tig welding with the foot pedal . It also arc welds in dc fine . When i switch to ac all I get is the hi frequency arc and maybe 20 amps on the gauge . I also tried arc welding in ac and got nothing . I even tried with out the foot pedal and nothing . I get different info that the pulse modules also called fc1 fc2 or gate drivers part number 000105 must be fine and the scr or in manual they call thyristor part number 000251 must be fine if they work in dc. . Does any one no how to check voltage coming out of the printed circuit board ( pc1 ) then going to the pulse modules then to the thyristor . One person said if all 4 scr must work in dc and ac . One person said the 2 scr on the right are for dc and the ones on the left are for ac . I have cleaned all connections on the ac dc switch , polarity switch , out of transformer and pulse module . Thanks for any input

  • #2
    All 4 SCR's are for DC. You bypass that bridge to weld in AC. Your problem has to be in the polarity switch. It's just straight AC going to the output studs.
    I feel you are not getting a solid connection through the switch. Make sure the HF is off and check the OCV in AC. If the OCV is good than it's a connection

    Comment


    • #3
      I checked the voltage from work terminal and electrode terminal while machine is in ac ..The voltage in ac without pedal pressed is zero .When I press the pedal I get 75 volts ac The strange thing is on the machine the voltage gauge reads 35 volts . Then when I switch to dc without the pedal pressed I get o volts . When I press the pedal I get 35 volts dc and the gauge on the machine reads 35 volts . I am not sure why in dc the voltage gauge works correctly while in dc, But then in ac the voltage gauge reads about half what I get on my hand held meter .I cleaned the polarity switch before and will clean and check it again.. In the manual it states while in ac it it bypasses the polarity switch so it doesnt matter where the switch is placed . So i thought that at first could not be the problem .

      Comment


      • #4
        Need your welder's serial number. I picked a random Sync 300 manual, and there is an AC/DC switch on the panel. Your problem almost has to be in that switch or associated wiring, unless your machine doesn't have that switch.

        Comment


        • #5
          Thanks for the help . The serial number is jd683309 the welder is a 300 sycrowave from 1983 . It has the switch and I unbolted and cleaned every connection and even replaced almost every bolt. Between the bolted surfaces it looked good . I have 2 sycrowave 300 welders and they both do the same thing no ac . I only have 1 pc1 printed circuit card so when I use the one card in either machines they weld in dc but no ac . I am wondering is there something on the pc1 board that allows the welder to work in dc but not in ac . I have 2 boards and one doesnt weld in dc or ac . One board welds only in dc . I have a friend who will look at the board but wants a schematic. but the owners manual doesnt have that .

          Comment


          • #6
            The manual for your machine is here:
            https://www.millerwelds.com/files/ow.../O350L_MIL.pdf\
            and it has a schematic for PC1 right up front before the table of contents, so that may enable your friend to dig into it.

            My initial thought was the same as 1997CST--don't need the rectifiers (actually, SCRs in this machine) for AC, only DC. However, a look at the schematic says the SCRs are also used for AC-their gate drive signals are modulated to control/adjust the weld current. Therefore, they have to have gate drive signals for either AC or DC to work, and those drive signals come from PC1. Making those signals wider increases output current; narrower decreases. So, if your friend has an oscilloscope, it should not be too hard to find out what's going on. Since this machine is old enough that the guts are transformer isolated from the power line, there is no issue with putting a scope ground on PC1 pin 35, and one vertical channel each on pins 33 and 34. The SCRs are always turned on in pairs; each of those two pins drives one pair, so looking at those two signals should tell the story. I'm suspecting there is something wrong on the board and you won't see any gate drive on AC. At least that's a starting point.

            Comment


            • #7
              Its likely on a board. I doubt if my guy made notes, I bought mine broke with a manual and someone had worked on it or replaced it at some point. Its been so long ago I dont recall exactly what went wrong but seems it was no output on AC like you describe and my tech said,,,, 50 cent transistor or resistor maybe, some little widget on the board anyway. Worked fine ever since.

              Comment


              • #8
                Thank you every one for the advice , Thursday I am putting a scope on the wires that come out of the pc board and go to the gate drivers and thyristors . I hope we can find out if its the pc board giving us troubles . If the pc board is giving a signal then in might be the scr or thyristor . I have been told it could be a bad connection but have cleaned all the connections .I have not checked between the wire and crimped on bolt eye lug .

                Comment


                • #9
                  If it's welding OK on DC, seems the SCRs/Thyristors must be good. Same parts in that area work for both AC and DC, but the AC gate drives must derive their inputs from a different source. The drivers themselves have to be OK for DC to work. Anxious to hear what you find. Check the gate drives on both DC and Ac so you can compare.

                  Comment


                  • #10
                    My guy repaired the board. It was 20 yrs ago and I remember something about 50 cent part. Was something we had in stock or used.

                    Comment


                    • #11
                      Thanks everyone for the input . We put a scope on the wires and the readings my friend thought was strange . All the readings is with the pedal pressed . We checked the wired out of the pc board to the gate drivers (fc1 and fc2 ) . The first test was on fc1 .The wire out of pc 33 becomes 122 and checked in between there and 35 out of pc that becomes 42 on gate drivers. On dc we got a dc pulse and seem a square wave. On ac we got nothing . Then out of the wires coming out of gate drivers going to #4 scrs labeled g and k we got 15 volts in dc nothing in ac . On the others wires g and k that I think go to #3 scr there is no output in ac or dc . On the other gate driver the wire out of pc 34 that becomes # 124 on gate driver to wire out of pc # 35 that becomes 42 on the gate driver . We got what my friend called open noise . In both ac and dc it seemed to read 50 volts. Then the wires to Ithink scr #2 labeled g and k in ac we got nothing and in dc 15 volts . Then the wires labeled g and k going to scr labeled #1 we got in dc 15 volts and in ac nothing . My friend thinks part of the strange readings was some dirty connections . I am going to clean the connection and try again in a couple days . We just ran out of time trying to first figure the schematic and are not even sure what path the power takes . If any one can figure something out that would be great .............thanks alot

                      Comment


                      • #12
                        I am still wanting to try the oscilloscope again now that I cleaned more connections . I was trying to figure on the schematic how the power flows to the gate drivers then to the scr thyristors and then out of the machine . When I look it seems there are more then one paths so that makes no sense . I ran the welder in dc on hi for a while . I then tested what parts were getting hot . It seems scr number 3 and 4 raised 10 degrees and the main diode raised almost 40 degrees . I wonder if this means scr 1 and 2 are not ment to be working in dc . Or that they are suppose to be working but are broke . When in dc it does weld with full power so its seems to be working correctly . it would be nice to know exactly when the scr are working when in dc and in ac . Thanks any input

                        Comment


                        • #13

                          To clarify your post above a bit, the welding power does not flow to the gate drivers-only "samples" of the voltage go to the gate drivers from the cathodes of the SCRs. The gate drive signals originate at the big PC board and get "processed" by the gate drivers and sent to the gates of the SCRs. . Welding power only flows through the transformer, SCRs (two at a time, depending on which half cycle of the power line, positive or negative), through the arc itself, and through the Hall device current sensor.

                          Here's how electrons flow (negative to positive from/to the secondary winding of the transformer) in AC, all the way through the circuits and through the arc itself. . Hope this helps you see what's going on. If you need the DC paths, I can do them for you later-not enough time now. Separate diagrams for positive and negative half cycles of the power line.

                          I haven't traced the paths yet, but I assume all four SCRs have to work for normal operation in DC also. The fact that 1 and 2 are not getting warm is suspicious, and I'm wondering if you are in fact welding at full power in DC. The SCRs conduct in pairs--1 and 3, and 2 and 4 in AC, and I suspect it's supposed to be the same in DC. Definitely worth more investigation.

                          Comment


                          • #14
                            Thanks Aeronca that helps alot . I had no idea there was 2 schematics for ac because the the different flow of electrons . Now it makes a lot more sense . On the green copy it cut off the z2 reactor and couldnt tell if power went threw there . It would be great to see how the power flows in dc . On my comment last I schould have said it better of the flow of welding power . The wires to the scr are very small . Now I see why you say all 4 scr work in ac.

                            Comment


                            • #15
                              Yes, I don't know what happened -- I must have pasted a piece of "white space" over the reactor. Here's the green one with all the parts.

                              I'm doing the DC ones now--there will be four diagrams, because you have to trace both DCEP and DCEN, for both the positive and negative half cycles of the power line. Will post shortly.

                              Comment

                              Working...
                              X