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Arc start problem in TIG 250/250 Lincoln

Mud

Diamond
Joined
May 20, 2002
Location
South Central PA
I've had this Lincoln TIG 250/250 forever. The small red one. Bought it used from a welding supply house after it was in for an unknown repair from the previous owner who didn't pay the bill.

Currently It has an erratic problem with starting the arc. We use it 99% for steel, max of an hour a day. With the spark set to start only on DC it often requires 2 or 3 hits of the pedal to fire the arc, sometimes I hear it arc for a second and then stop. On continuous AC, same thing, sometimes works correctly, sometimes not at all, sometimes just for a second. When the arc is not firing, I can't even scratch start the arc at the electrode. With the spark set to off, I can sometimes scratch start it, sometimes not, so it seems to not be in the spark system, but in a contactor somewhere.

So what could cause this problem, is there something I can attend to myself without hauling it in to a repair facility?

Also - We cleaned the arc gap and set it, no change. With the cover plate off, I sometimes see the arc jumping from around the body of one contact to the body of the other contact instead of just across the closest part of the gap - Is that normal?
 
I'd open it and try to find the problem, I don't know if those had any solid state stuff in them, old capacitors and such?. Probably is simple enough either way. Probably needs a good dusting anyhow.

I think the contacts/points whatever they're called for the arc gap can be replaced. I never got to see how they really worked in action as I was usually the one welding, just knew it was in there on the old syncrowaves.
 
When you hit the pedal, do you always here the contactor make?

I'm guessing from your description that the arc start contactor is getting fuzzy. Might get by cleaning but best would be to replace.

Download the schematics from Lincolns website and go from there. Should be a very easy fix.
 
Might not hurt to also check everything is ok with the pedal/cables and such, intermittent issues are often related to something like that too.
 
Might not hurt to also check everything is ok with the pedal/cables and such, intermittent issues are often related to something like that too.

I moved the pedal down the list since the problem also occurs in local mode when scratch starting. I f the pedal is wired they way most welders are, the plug, wires, and pedal should have no effect unless there is a jumper in the plug that is bad but that is very unusual.
 
If the HF is jumping around inside, it might be a bad ground or you may have dust all over the guts of the welder letting the HF jump to ground internally.

I put a car together many, many years ago at a shop I was working in. Absolutely would not start. Went over everything and finally opened the distributor because there was no fire on the plugs. A guy had painted a small truck with charcoal metallic paint a couple of weeks earlier. The metallic overspray inside the distributor cap (that was laying in the shop when he sprayed) was letting the distributor fire to ground inside the cap. Wiped it out with laquer thinner and it fired up and ran perfectly.

A friend bought a Miller Big 40, with leads, on a trailer for $300 because it wouldn't weld. Engine ran, everything worked, just wouldn't weld. The 110V plugs would even run a drill motor. Turned out to be corrosion in the ground clamp. $17 clamp and it welds like a brand new one. Check your cable connections on BOTH ends.

Last suggestion would be to check the pedal cannon plug. My Hobart Tigwave quit working one day after a few months of flawless operation. One wire had pulled out of the cannon plug. Fifteen minutes with a soldering iron and it was good as new.
 
Thanks for the suggestions. I'll start with the schematic, that didn't even occur to me that it would be available.

I've dealt with pedal/cable problems on another Lincoln, this doesn't feel like that but I'll test further.

The contactor sounds the same whether it starts or not. And I am less suspicious of the spark unit because it's hit or miss even with the spark turned off.

The welder is buried under a workbench and will take some effort to get out to open up. We've still been using it even with the erratic operation, so we'll need to find some free time to get to investigate.
 
If the contactor is always sounding like it is making when it should, then it is highly probable that dirty contact points are the issue. Sometimes wiping clean will work but best solution is to replace contactor.
 
My experience with industrial TIG welders to date is 100% of this category of problem have been due to the torch lead broken inside the insulation. Sometimes due to obstructed cooling flow & melting the lead, sometimes due to something heavy & sharp dropped on it.
 
My experience with industrial TIG welders to date is 100% of this category of problem have been due to the torch lead broken inside the insulation. Sometimes due to obstructed cooling flow & melting the lead, sometimes due to something heavy & sharp dropped on it.

I've seen crazy torch lead problems too. But how could that cause the spark to fail to fire, or stop firing once it has started, when the lead is no where near a ground? It's an air cooled torch. I can hear the spark, and I can see it when the cover is open.
 
"When the arc is not firing, I can't even scratch start the arc at the electrode. With the spark set to off, I can sometimes scratch start it, sometimes not, so it seems to not be in the spark system, but in a contactor somewhere."

There you go. Intermittent lead or ground contact. When the lead makes contact, it works. When the lead is open you get no power through the torch at all. When it makes contact due to a particular way the lead is hanging or the torch is held, it works. When it goes open, the HF still fires, but you get nothing at the torch.
 
Understood, but the HF will sometimes not start, or will start and then stop of it's own accord. According to the sound of it. Whether the electrode is near a workpiece or not.
 
HF will fire no matter what. My Tigwave will throw a 2" long fibrous HF arc if the ground is still hanging on the machine. If the torch lead is intermittent, it will do exactly what you are describing.
 
If the torch lead is going open, that is EXACTLY what it should do. It's acting like there is no torch lead on it, so nothing changes when you take the lead off. I'd sure try to borrow another torch/lead and see what it does. If it still does it, it might be a contactor or relay, or it might be a bad board. I think I'd also pull the machine out of the hole and blow it real clean with an air hose after vacuuming it out real good (so you don't just blow all the dirt deeper into it). Could just be years of minute metal grinding dust particles forming a bridge and shorting something out internally.
 
If the torch lead is going open, that is EXACTLY what it should do. It's acting like there is no torch lead on it, so nothing changes when you take the lead off. I'd sure try to borrow another torch/lead and see what it does. If it still does it, it might be a contactor or relay, or it might be a bad board. I think I'd also pull the machine out of the hole and blow it real clean with an air hose after vacuuming it out real good (so you don't just blow all the dirt deeper into it). Could just be years of minute metal grinding dust particles forming a bridge and shorting something out internally.

If the torch lead is open, the high frequency will still fire. The OP's welder is firing sporadically with and without the lead. This implies that the problem is further upstream not saying he doesn't have some lead problems but primary problem is likely not the leads.

It is likely that arc power is not being turned on when required.
 
Could be the polarity switch

Try it in AC or the other DC

Can usually fix by repeated turning the switch.

The contractor is in the back and accessible when you take off the panel to switch voltage contacts are right

There and accessible with a few screws

The ground lead and torch lead are still suspect but both are tied to the polarity switch.

If it starts to work scratch starting but you still get no HF jump start the first time but you get it

The second start than the big capacitor is week.

There are 2 boards in the front accessible by removing 4 screws I have had the one on the left that controls the amps

Loose contact at the fuse that is mounted on the board.
 
We have it apart, the contacts in the contactor are beyond worn out. Is there any hope of getting just the contacts somewhere, or do I need to buy the entire contactor? The PN is M12161-23, which is replaced by M12161-63. Cost is over $400, which has me contemplating replacing the entire welder.
 
We have it apart, the contacts in the contactor are beyond worn out. Is there any hope of getting just the contacts somewhere, or do I need to buy the entire contactor? The PN is M12161-23, which is replaced by M12161-63. Cost is over $400, which has me contemplating replacing the entire welder.
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Most of the internal contactors are off the shelf contactors. Look for manufacturer and model, should be able to replace contacts. If they are unavailable most any properly sized contactor will work. Just make sure coil is correct voltage.
 








 
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