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Syncrowave 250 full amperage output KB057067

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  • Syncrowave 250 full amperage output KB057067

    I am trying to fix a 1991 Syncrowave 250. It has no amperage control. The welder was working and suddenly, went full output. I am quite competent in electronics and repairs and need a few hints as to the operation of the control board (135254). I am aware of the fact that the PCB common is NOT at chassis ground potential and the associated dangers with this.
    As it is an older welder, it uses the shunt to detect current flow. It has the problem whether it is pedal or panel control of amperage. The output control works as releasing the pedal will stop the output. The usual things check out such as +15 V, - 15, +10V. Panel controls seem to have proper voltages, non symmetrical -15VDC and +6VDC on the AC balance potentiometer. I disconnected the shunt and applied a small voltage to the feedback pins to simulate between 100 - 200 amps (1.3VDC per 100 amps feedback). This would trick the board into thinking it was supplying 100 amps of welding current. By changing the panel control, it should have changed the firing angle of the SCR's thereby reducing the average output voltage. This had no effect. Knowing what systems are working on the control PCB, I need to figure out specifically where the panel setting and feedback control firing of the SCRs. I could probably change out OP amps and the dreaded Tantalum capacitors which are notorious for shorting out but I would rather troubleshoot this and specifically replace the damaged components. Any help would be appreciated.

    PS anyone have a better digital copy of the schematic than what is in the online manual? Quite difficult to make out pin numbers, etc.

  • #2
    I am far from an expert but since no one else has chimed in. I think it may be the "Hall device". If you do a search for (hall device) on this forum you will find many threads on full output syncrowaves. Hoping someone with more tech knowledge will come along soon.
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    • #3
      No Hall device on this year. Shunt resistor instead. Nevertheless, thanks for responding. I was starting to feel very alone on this group.

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      • #4
        Originally posted by mewanchyna View Post
        No Hall device on this year. Shunt resistor instead. Nevertheless, thanks for responding. I was starting to feel very alone on this group.
        I wish I could help. But you aren't alone. I miss Cruizer
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        Just a hilljack in the woods with fancy welding equipment
        and a pet Raccoon.

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        • #5
          Assume you are looking at the gate drive signals with a scope? I’m on the road and unfortunately can’t try to help much for several days. Have you tried looking for changes in the input voltage to the op amps as you vary the front panel amps control?

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          • #6
            Good to hear from you again Aeronca.

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            • #7
              I haven't put my scope on the gate drive signals yet. I checked all voltages from front panel controls and switches. They all check out fine, including the current adjustment potentiometer.

              From the schematic, the feedback voltage from the shunt goes into one op amp and is sent to the control circuitry. It is also sent off to another op amp to drive the accessory current meter. As I do not have a way to load the output, I detached the shunt feedback and replaced the feedback voltage with a variable power supply (floating) to simulate current flow through the shunt. I was hoping that this would trick the circuitry into changing the firing angle of the SCRs. I looked at RMS voltage at the output hoping to see a corresponding change when I changed the feedback voltage. It sat there at 75VAC. However, this was under a no load situation. I reassembled the shunt circuitry and put a stick electrode and tried SMAW at the lowest current setting. It was evident that it was running full output. I am assuming that there is no change is firing of the SCR but maybe I should verify with the scope.

              I imagine that the welder needs current to be flowing before and SCR firing angles are changed, right? It must start full output and regulate the current within the first several microseconds once the shunt voltage spikes up as current starts.
              Next, I am sorting out where the feedback and current setpoint from the panel meet to make the decision on firing the SCRs. I know they get timing signals from the tap from the transformer. There is an op amp that integrates this signal.

              I am at the point of sorting through the schematic to identify the operation of each section. This is long and tedious. Together, I am sure I will get it up and running.

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              • #8
                You can invent a load bank for testing. Metal plates in salt water is the old-fashioned solution - just get two pieces of scrap plate that fit nicely a few inches apart in a 5-gallon bucket, clamp the stinger and ground to them, fill with water, add a pound of salt, let dissolve. Will produce nasty, flammable fumes - do outside!



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                • #9
                  Originally posted by Bushytails View Post
                  You can invent a load bank for testing. Metal plates in salt water is the old-fashioned solution - just get two pieces of scrap plate that fit nicely a few inches apart in a 5-gallon bucket, clamp the stinger and ground to them, fill with water, add a pound of salt, let dissolve. Will produce nasty, flammable fumes - do outside!
                  If I'm not mistaken, that will create bubbles of HCl gas (if dissolved in water, HCl = hydrochloric acid) and leave a solution of NaOH (sodium hydroxide, or lye) in the bucket...

                  NaCl + H20 + energy --> HCl (gas) + NaOH
                  Last edited by Helios; 08-16-2021, 06:00 AM.

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                  • #10
                    Originally posted by Helios View Post

                    If I'm not mistaken, that will create bubbles of HCl gas (if dissolved in water, HCl = hydrochloric acid) and leave a solution of NaOH (sodium hydroxide, or lye) in the bucket...

                    NaCl + H20 + energy --> HCl (gas) + NaOH
                    Actually, I think it is Chlorine gas and NaOH. Nice combination. In any case, something to do outside.

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                    • #11
                      Originally posted by mewanchyna View Post

                      Actually, I think it is Chlorine gas and NaOH. Nice combination. In any case, something to do outside.
                      Actually, in a bucket, you're going to get hydrogen and chlorine, which I'm pretty sure will immediately combine into HCl. (There aren't many more reactive elements than H and Cl ... especially in each other's presence. If not...well, hydrogen is pretty darn flammable and chlorine is choking!)

                      And lye (aqueous).

                      Click image for larger version  Name:	yx1rjeiosbio9z4vfcpk.png Views:	0 Size:	89.9 KB ID:	616633
                      Last edited by Helios; 08-16-2021, 10:08 AM.

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                      • #12
                        Originally posted by Helios View Post

                        Actually, in a bucket, you're going to get hydrogen and chlorine, which I'm pretty sure will immediately combine into HCl. (There aren't many more reactive elements than H and Cl ... especially in each other's presence. If not...well, hydrogen is pretty darn flammable and chlorine is choking!)

                        And lye (aqueous).

                        Click image for larger version Name:	yx1rjeiosbio9z4vfcpk.png Views:	0 Size:	89.9 KB ID:	616633
                        So don't breath or light a match. Did I mention that I hated Chemistry in school.
                        Last edited by mewanchyna; 08-16-2021, 10:39 AM.

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                        • #13
                          Old theaters used to use salt water dimmers, before rheostats and variacs were used. Just a tube of salt water, two plates, and a lever to raise and lower one of them. I think that, with AC in a bucket, most of the HCl and NaOH recombine pretty quickly. It's probably a lot messier with DC. You should still do it outside, either way.
                          Last edited by Bushytails; 08-16-2021, 02:42 PM.

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                          • #14
                            Originally posted by Bushytails View Post
                            I think that, with AC in a bucket, most of the HCl and NaOH recombine pretty quickly.
                            Interesting. So I guess the cathode would turn into the anode 60X/second and the anode would turn into the cathode 60X/second. I'd be interested to see exactly what would happen in that scenario. I suspect it would just create a lot of heat, which is probably the best outcome if you want a resistor/load bank. I bet the saltwater would get hot fast!

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                            • #15
                              Hi All, After doing some strategic part replacement, I have tested most portions of the circuit and portions of the circuit seem to work as expected. Unfortunately, the manual gives little information as to calibration, which I think may be another problem. I think the potentiometer, which I think is for amperage adjustment as is biases the voltage reference going to the op-amp/ comparator which takes care of firing angle.
                              Looking at the schematic, this is what I figured out for adjustable resistors.
                              R3 current feedback voltage adjustment
                              R4 - current calibration for main output
                              R5 - fixed 10VDC adjustment
                              R9 -optional currant meter adjustment
                              R33 open circuit DC voltage adjustment

                              I think I got most or all of them. I know which ones do not affect the overall functioning of the welder. Does anybody have a calibration method? I assume the ones that are important are R3 and R4. I think R33, open circuit voltage adjust may be needed to detect a welding/arc condition. I have to figure out what specifically this affects.(Maybe high frequency trigger?)

                              Once again, any help would be appreciated.

                              Mark


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