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Hobart beta mig 170 repairs

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  • Hobart beta mig 170 repairs

    https://youtu.be/w6KJOr8tqAM
    Hello all,
    Was hoping to get some help repairing the control board off of my Hobart beta mig welder, here is the schematic of the board. I have replaced the Q8 and Q9. Q8 being the wire feed darlington power amp, TO 220 case, and is a PNP D45E3. The schematic shows this to be an NPN D44E2, the BOM from the manufacture show this to be a PNP, I also checked with the factory tech he stated there was a misprint on the schematic and gave me the correct component number for the Q8 location. Repaired/replaced the copper braiding end crimp connectors on the wire feed cable assembly as this copper braided wire serves to feed high amperage from one end of the wirefeed cable assembly to the other end (tip end). Was having issues with the wire locking up in the cable core because of the core flowing amperage instead of the copper braiding, this would cause the core to heat expand and lock up the wire, so the cable feed is good now. I was not able to weld 1” before I repaired the cable feed, now I can weld about 6”, then the wire feed motor starts to shutter, slow and stop. I can the release the gun trigger, pull the trigger again and start again, same thing happens. The wire feed motor pulls 4 amps @ 18.3 volts DC under load @ max speed, with no load the motor runs fine, the motor is rated for 24 volts DC, the D45E3 is rated for 10 amps, this should be good enough. I’m thinking something is going wrong with U1, TL494CN. When pulling the trigger on the gun, that feeds + voltage to J4-1 and - voltage J4- 2. I have voltage present when pulling the trigger on the gun. If I cannot repair this board can someone recommend a speed control board that I could use in conjunction with this board, just to control the wire feed alone? I checked incoming voltages to the board, most pins on J1, 1 through 12 and have 27 volts AC, one has 55 volts AC. This does not make since to me, I only see two diodes on the board to rectify the voltage to DC or am I missing something? The 6 pins on J2 are the potentiometers, 1 through 3 for voltage control and 4 through 6 for the wire feed. J5 and J6 are the wirefeed motor voltage. I have searched the internet and cannot find a wire feed control board to marry to the board I have. Hope you guys can help. Thanks, Jeff. Click image for larger version

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    Last edited by jeff-; 10-09-2017, 11:09 AM.
    sigpicJeff's CNC Plasma Cutting

  • #2
    Originally posted by jeff- View Post
    ...I checked incoming voltages to the board, most pins on J1, 1 through 12 and have 27 volts AC, one has 55 volts AC. This does not make sense to me...
    Diagnostics on this machine are most certainly not my area, but I do note that 27.4 * 2 = 54.8.

    Could it be that your "27 VAC" and your "55 VAC" are just line-to-ground and line-to-line, respectively, and normal for transformed control voltages?
    Last edited by MAC702; 10-09-2017, 01:05 PM.

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    • #3
      Yes that is my thinking as well. I’m going to replace U1 and a couple of other components and try it again.
      Last edited by jeff-; 10-22-2017, 10:36 AM.
      sigpicJeff's CNC Plasma Cutting

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      • #4
        Made some progress repairing the control board. Replaced the IC’s TL494CN location U1, LM324N location U2, LM317T location U3, TIP122 location Q6, 2N6668 location U8, 2N6292 location U9. Also made some modifications to the board. In case any of these IC’s go bad again I will not have to unsolder and resolder components as I soldered in plugs for U1, U2 and U8. U8 also soldered in a leaded plug and installed another heat sink as I suspected It could have been overheating a bit. I might even install a little 24volt fan to blow on the board to keep it cool. Well hope this will help others with the same problems.

        Click image for larger version

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        Last edited by jeff-; 10-22-2017, 10:45 AM.
        sigpicJeff's CNC Plasma Cutting

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        • #5
          Well got my mig welder up and running. Wire feed works great now. After all the electronic components I had replaced, about 16 in all, I still had a problem with the wire feed stopping after about 12” of weld from a cold start. Took the feed motor off, tore it down, found nothing wrong, greased it and put it all back together. It really acted like something was overheating and breaking down, opening the 24 volt circuit. After welding about 12”, I could release and pull the trigger on the gun, the wire feed would start for a second then stop, spit and sputter. So I started checking other items besides the board, what the 24 volt transformer power was going through before it went to the board. Started lightly wiggling wires, all of a sudden one side of the thermal disk broke off, disk is between the two SCR’s mounted to the aluminum plate, this was breaking down and opening the circuit-24 volts to the board. Well I happened to have some disks from past work I have done, drilled out the rivets on the old disk, installed the new one with screws, plugged the wires into it, fired up the welder again, I welded 3 different paths of 12” long welds with no problems, so all the time and effort finally paid off. I now have a good welder that was given to me as they said it was junk. I want to thank Keith for the schematics and other people who had problems and the Hobart techs who helped them and posted on this forum about this welder, because without reading these posts, learning from the help and advise they got, I really doubt that I could have repaired this welder. Thank you all, really appreciate it.Click image for larger version

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          sigpicJeff's CNC Plasma Cutting

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          • #6
            Maybe you should start a board repair/recovery business on the side....

            Dale
            Lives his life vicariously through his own self.

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            • #7
              Dale thanks for the vote of confidence, but I don’t think I would make any money as long as it took for me to get this welding machine repaired, there was quite allot wrong with it. The transformer aluminum leads were melted off at their connections so I had to pull the transformer out, cut the melted parts off, there was still enough aluminum lead wire to reconnect them. Took a steel bar and hammer, flattened out the leads, drilled holes in them, reinstalled the transformer and reconnected the repaired leads. It did work and worked well to my surprise. So it took allot of enginuity to get this one going again. Thanks for the support.
              sigpicJeff's CNC Plasma Cutting

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              • #8
                What an inspiring thread! Nah, I'd still just stare at it...

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                • #9
                  Well I did allot of stairing and head scratching before I got it working good.
                  sigpicJeff's CNC Plasma Cutting

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                  • #10
                    Just got an answer from Keith about temp cut out and in on the thermal disk, here is a direct quote= The thermostat on the SCR heat sink is a normally closed thermostat that opens @195F and closes @175F.

                    Thanks so much Keith.
                    sigpicJeff's CNC Plasma Cutting

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