http://www.joethewelder.com/?p=205
I have an old wire feed welder I bought when I was in my 20's, (long time ago) and it stopped working. Last spring I found mice had made a nest in it and hence caused a connection to the low voltage transformer to fail. I was able to dig the end of the coil loose, and make new connection and everything was fine. I went to use it for the first time since I repaired and tested it last week, and again no workee. This time the issue is the wire won't feed either by trigger or momentary feed switch. Attached you will find a link that has the schematic, component description, board layout, and some diagnostic procedures. The first thing it says is if there is a wire feed issue, to replace the off board transistor. That has been done, and no change. It is listed in layout off the J5 plug. Pin 3 has 30 volts dc, does not change when momentary is engaged. Pin 2 is 2.7 mv no change during switch engagement. Pin 1 is 2.7 mv drops when switch engaged to near zero.
I do have good board ground, regulated 23.7 volts on high side. The issue is that under no circumstances can I get and voltage to what is listed as j3, which supplies the power for the feed motor. On a hunch today, I replaced the Q2 transistor because it is the last item to switch the power to that terminal. again no change. This leads me to believe that Q2 is not being triggered properly. I don't know enough about the functions of the parts combined to know where to look next. I do know what diodes do, and resistors etc, but not how they impact each other in a combined fashion. I can include a photo of the actual board if that is needed, but there are no obvious signs of "letting the smoke out", the capacitors are not swollen on the ends, and they seem to charge ok when shorted the connected to dvom, the voltage rises and holds.
This puts me at a loss as where to go next, I have exhausted my current knowledge. I would be extremely appreciative of any insight you can give me whether it just be "replace part x" or a more detailed assessment of how the system works, and why it is not. ( I love to learn new things, but don't want to waste your valuable time)
Last thing you need to know for sure is the 2 momentary switches shown in the first pic, are reversed in labeling. The one for the wire feed (inch) is actually the connections on right side of board, and gas purge is actually on left side of board. (both are shown to be the opposite in the diagram.
Look forward to hearing from you.
Thanks much!
MORE INFO
Upon further looking, (with my limited knowledge), it seems to me that with the off board transistor, pin 3 should be voltage in which is reading the 30vdc, and when momentary request is pushed it seems to be grounding pin 1. Should that not then produce a voltage output change on pin 2? It is in a socket rather than hard soldered, if pin 2 should get voltage change when pin 1 is grounded, maybe it is defective socket.
I have an old wire feed welder I bought when I was in my 20's, (long time ago) and it stopped working. Last spring I found mice had made a nest in it and hence caused a connection to the low voltage transformer to fail. I was able to dig the end of the coil loose, and make new connection and everything was fine. I went to use it for the first time since I repaired and tested it last week, and again no workee. This time the issue is the wire won't feed either by trigger or momentary feed switch. Attached you will find a link that has the schematic, component description, board layout, and some diagnostic procedures. The first thing it says is if there is a wire feed issue, to replace the off board transistor. That has been done, and no change. It is listed in layout off the J5 plug. Pin 3 has 30 volts dc, does not change when momentary is engaged. Pin 2 is 2.7 mv no change during switch engagement. Pin 1 is 2.7 mv drops when switch engaged to near zero.
I do have good board ground, regulated 23.7 volts on high side. The issue is that under no circumstances can I get and voltage to what is listed as j3, which supplies the power for the feed motor. On a hunch today, I replaced the Q2 transistor because it is the last item to switch the power to that terminal. again no change. This leads me to believe that Q2 is not being triggered properly. I don't know enough about the functions of the parts combined to know where to look next. I do know what diodes do, and resistors etc, but not how they impact each other in a combined fashion. I can include a photo of the actual board if that is needed, but there are no obvious signs of "letting the smoke out", the capacitors are not swollen on the ends, and they seem to charge ok when shorted the connected to dvom, the voltage rises and holds.
This puts me at a loss as where to go next, I have exhausted my current knowledge. I would be extremely appreciative of any insight you can give me whether it just be "replace part x" or a more detailed assessment of how the system works, and why it is not. ( I love to learn new things, but don't want to waste your valuable time)
Last thing you need to know for sure is the 2 momentary switches shown in the first pic, are reversed in labeling. The one for the wire feed (inch) is actually the connections on right side of board, and gas purge is actually on left side of board. (both are shown to be the opposite in the diagram.
Look forward to hearing from you.
Thanks much!
MORE INFO
Upon further looking, (with my limited knowledge), it seems to me that with the off board transistor, pin 3 should be voltage in which is reading the 30vdc, and when momentary request is pushed it seems to be grounding pin 1. Should that not then produce a voltage output change on pin 2? It is in a socket rather than hard soldered, if pin 2 should get voltage change when pin 1 is grounded, maybe it is defective socket.
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. I will get a round tuit eventually. At the present I am mending an Alba valve radio (only 280V!) and also a picture frame, I need to be awake to use a biscuit jointer.
