Lincoln 300/300 tig help
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  1. #1
    Join Date
    Dec 2018
    Location
    Ms
    Posts
    11

    Lincoln 300/300 tig help

    Being new I posted this in electrical. I can still use some help. I'll recap, I bought the welder and fired it up. It worked buy I didn't pay attention to the foot control. I decided to tear it down and paint it. When we took it apart we found all of the wiring decaying and rotting. I retired one at a time except one wire. a guy helping me was holding 2 wires and I asked where they went. He didn't know. Anyway we get it all finished and it welds great except the foot control doesn't vary the amperage. I checked it with an ohm meter and both legs vary the ohms. The machine does vary amperage with the rheostat fine adjustment control. I called Lincoln tech and they sent a schematic but it's not the correct one. Some of mine is destroyed. I attached another schematic I found that is the same as mine. If anyone can help point me in the direction of what varies the current I would appreciate it. I do have one wire each that go from the current adjustment and the bottom post of the remote start switch that go to the same pole on the yellow contactor. I don't know what this is but it does close with the foot pedal. [ATTACH=CONFIG]1696664[ATTACH]Name:  image.jpeg
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    Last edited by Robert61; 01-10-2019 at 11:38 AM.

  2. #2
    Join Date
    Mar 2015
    Posts
    606

    Re: Lincoln 300/300 tig help

    Is the switch on the front panel set to remote?

  3. #3
    Join Date
    Dec 2018
    Location
    Ms
    Posts
    11

    Re: Lincoln 300/300 tig help

    Yes. As I stated the foot control closes the output contactor and it welds great it just won't vary the current. I did get pics of the inside of another welder and now the schematic makes sense. The original wires had a number on them. Unfortunately the wiring in my welder was rotten and crumbling away. There were no numbers on them. I should be able to sort the wiring out. I'm not an electronic guy at all. I don't know what the amptrol varies if it is working. I'm thinking the 2 solenoid controlled switches are the pilot relay but I'm not sure about this.
    Last edited by Robert61; 01-12-2019 at 10:48 PM.

  4. #4
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,357

    Re: Lincoln 300/300 tig help

    Think of the diagram as a road map. Follow the lines like a road.
    Start at the supply lines. Work your way down to the first transformer. This is the main weld transformer with an aux winding that supply all the lower voltages needed. Just to the right of that is the main reactor, it set the welder output ranges. Top side windings go to the range switch. The bottom windings are the command windings. Just to the right of the main reactor is the magnetic amplifier. Works like a light dimmer to control the command voltage to the main reactor. Voltage from the main transformer goes through the windings on the left side and feed the diodes to the left. Turns the ac voltage from the mag amp into DC voltage needed to control the main reactor. The right side of the mag amp has the amp control rheostat, bridge diodes and bias resister. Above the control rheostat is the remote control select switch. If this welder works in panel control and you can turn the amps up and down
    All this is working. If it only acts up with the foot control plugged in and the switch set to remote. The we need to look at the switch and the foot control wiring.
    Put ohmmeter on the foot control plug. measuring the pins. One set will be shorted, one set will have a fixed restance value one set will have the same value but it will change with the peddle. the short should increase in value. you most likely have a problem in the foot control current circuit. The switch circuit is ok. If foot control tests out good then look at plug and wires to the switch and the switch. switch is a two position on/on switch. Rheostat should have approximately 30vdc end to end. same voltage goes to the foot control.

  5. #5
    Join Date
    Dec 2018
    Location
    Ms
    Posts
    11

    Re: Lincoln 300/300 tig help

    Now that I can see what the schematic is showing its going to be a huge help. I posted the pics so someone such as yourself could tell me what different items are. Am I correct in thinking the yellow solenoid is part of the pilot relay? I have ohmed the foot control off of the machine and connected to the current control switch. It varies the ohms to the current switch. From there is where I feel like I crossed a wire. What is the name of the 3 transformer stack behind the lifting eye on top of the upper winding, it's the lower pic. I don't know why sometimes the pics are right side up and sometimes upside down.I think I either have one of these wrong or at what I'm calling the pilot relay. There are 2 solenoid in this box. When the pedal is pushed they both activate and the points move. I have a cad program and a cnc mill. I draw up and make parts. I made parts for jumbo jets for 18 years to the point of fabricating repair parts that are sometimes not made and having to get engineering and manufacturer approval. I wired my house completely. BUT when it comes to electronics I'm a da, and not a lawyer. My buddy, who is a retired high voltage splicer for the electric company, watching all of this says you can't just figure out where this foot pedal goes and what it varies? Duh see the da part again. Thanks for your input I do appreciate it.
    Last edited by Robert61; 01-13-2019 at 11:10 AM.

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