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Lincoln 140 HD WeldPak Diagnostic Troubleshooting

Discussion in 'Garage & Workshop' started by Tony, Sep 16, 2018.

  1. Tony

    Tony Administrator Staff Member

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    Here a while back I had used my welder to fabricobble up a bracket for my tractor so that I could put my water tank back there for my sprayer on the 3 point. A few days later, I needed to do a small repair on an electric wheel chair, I plugged in the welder, flipped the switch and I got nothing. No fan, no power, nothing!

    I started researching and found quite a few others that have had to replace the main board inside the welder. I have not done any serious diagnostics as of yet, but I'm getting ready to start working on it to see what the issue could be.

    If anyone has any ideas, post up and let me know. I'm pretty sure it is down to two parts. The main board, and the power switch. The main board is $170 and the switch is $6... Guess which one I want it to be :biggrin:
     
  2. Tony

    Tony Administrator Staff Member

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    I went ahead and brought the welder inside the house (because that is the best place for something that creates blinding light and sparks...) and sat it on the kitchen table (for the max "piss off the wife" points). First thing I did was start tracing wires from the outlet plug to the switch and then to the main board. The white wire on the outlet goes straight to the switch, and is switched to a wire that goes straight to the main board. The black wire (hot) goes from the plug to the circuit breaker and then into the main board, bypassing the switch. I thought they usually switch the hot and not the neutral....

    Continuity from the plug to the switch checked out just fine. So I started looking at the switch which was the next component in line to the main board (something I don't want to replace).

    The switch has two sides to it which are isolated from each other. The first side is the hot side from the white wire from the main outlet plug. It switches and allows angry pixies to head to the main board. The other side goes to the power selector switch on the front of the welder. I checked for continuity on the power selector side and when off I had no continuity, when on it did, just like it should. I checked the main power side and when off, no continuity and when on, still no continuity.

    At this point I decided to open up the switch to see how it was making contact. Some switches are really weird in how they work and the only way to know for sure is to look inside and see what is going on. Once I removed the front of the switch (just pops out) I was greeted with two contacts with two very heavy springs. I looked over everything with my "can't see shit up close" eyes and saw nothing wrong. Time for the old man glasses. I took a closer look now that I could see and I still couldn't really see anything.

    Sometimes with plastic switches, they will get hot and the terminals will melt the plastic causing them to not make contact. Everything in this switch was perfectly where it should be.

    The way this switch works is it has a spring right in the center and as you rock the switch to turn it on or off, it will move the brass contacts inside up or down via the spring. On the top (off), there is no contact, just plastic and the rocker tab(s) have a flat spot that holds them against the plastic. The center is a pivot point and this is where the power comes in and is always in contact. On the bottom (switch on, or flipped up) you have two soft pads on both the rocker and the terminal for it to make connection.

    These soft pads are soft to keep carbon buildup from happening, or that is the theory anyway. As I took a very close look at the contacts, I saw a very small little black dot on all 4 contacts. Obviously the power side was a little darker since it has to deal with the full voltage. But we are talking about black dots that are only about 1/4 mm (how do you like that, imperial and metric in one measurement :biggrin:

    With something that small, and on a soft pad to keep this from happening, I had my doubts that was the actual issue. But, I was there, I had some small screw drivers sitting there so I did some scraping. I cleaned off all of the contacts so they were nice and shiny silver again and put the switch back together. I plugged the plug into the wall (still in the kitchen mind you) and looked at @Bryan and said "what do you think? You think it's going to work?". He said something about keeping his pessimistic ideas to himself and I flipped the switch...

    Before you could even hear it, I saw the rear fan start to spin and I declared victory. The fan ramped up to its usual beautiful sound but that just means the fan spins. We have to test it to see if it is actually getting power to the transformer through the other side of the on/off switch. I grabbed the grounding clamp, I grabbed the gun, held them together, saw that Bryan was looking straight at it so told him to watch his eyes (we are still at the kitchen table!! This thing is heavy and if it didn't work, I didn't want to have to carry it back out to the garage then back to the house then back to the garage.... You get the idea) and I hit the trigger. Sparks went flying and we had success.

    Thankfully the main board is just fine and it was the switch that was the issue. A $6.00 part vs a $170.00 part, but I was able to fix it with a cheap chinese flat blade screw driver.... I think I'm going to order one of these switches though just to keep it on hand in case this happens again. I can just remove the old switch, install the new switch and test it before moving on to anything else on the welder.

    Happy ending, now it is time to make some molten metal!!!
     

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