Advice required for my trusty VARMIG 120

[chrisbond]

Hello,

Can I firstly say what a great site this is. Since finding the site from a link on the MGA board, I have learnt a lot more about MIG welders and welding.

My trusty MIG welder, which is 24 years old has developed a problem (reported on here before). For those who have never heard of the VARMIG range they are still made in Slovenia (although it was Yugoslavia when mine was made!), by Varstroj (http://www.varstroj.si/).

The fault that has occurred is that the feed wire now remains live when the trigger is released. I have been considering whether now was time to invest in a new one, but after reading the comments here on modern day machines and looking at the internals of mine in comparison to the SIP 130 shown on this site, I am having second thoughts. I have attached photos of the internals of the welder and I am interested in your comments.

Also, following some investigation, I think I may have tracked down what is causing the problem. When I removed the cover today, I noticed that the wire marked A in the top view photo had come detached from the resistor type thing, marked B. I have soldered this back on and tried some test welds, all was OK initially, but after a dozen or so short welds the old problem occurred and I discovered that this resistor (if that is what it is) had overheated.

MY questions are:
What is this part and can it sourced today?
Is it likely to be the cause or just a symptom of something else?
Do you think I'm wasting my time trying to get it repaired? (despite it age it is only in the last 3 years that is has had any major use, as I restore my MGA).

Chris

 

[Jake SS]

That is a "bleed resistor" which should be connected to a "normally closed" set of contact points, so that when you release the trigger it will discharge the capacitor, the big black round thing with 2 terminals on it. Otherwise the arc you are seeing is the capacitor discharging through your wire.

Would check the normally closed contacts to make sure that they "open" when triggered on and that they close when triggered off.

The resistor should be readily available, they are usually around 10-20 watts and 10-20 ohms

Would keep the welder you have already

 

[eddie49]

That looks like a well-specified and well-made machine, in excellent clean condition. As Jake mentioned, it has a capacitor on the output side, which will help to provide a smooth stable arc. You won't find that on a modern low-end MIG !

 

[R Kraft]

A stuck contactor will give those symptoms,some get dusty and stick.
Having power across the resistor all of the time would make it a lot hotter.
Robert

 

[chrisbond]

Thanks for your replies gentlemen.
I always felt it was a good quality unit, as it came my way via a UK resistance welding company (which unfortunately no longer exists), who tested it and found it to perform well.
Having no knowledge of electronics I have very little idea what each part does (expect for the basics), can you point out the contactor unit, so that I can check it out. If it is the contactor which is the problem, can it be repaired or does it need to be replaced? Also will the resistor need replacing?

Cheers

Chris.

 

[R Kraft]

The two blue things look like contactors one between the transformer and the wirespeed control, and the other is about half way down in the back.
You might try tapping on the tops of them, with a plastic screw driver handle when the welder is acting up and see if the spring inside will make it shut off.
Sometimes the contactors can be cleaned but you might be better off to replace a bad one.
Robert

 

[chooowie]

Gorenje used to build some excellent welders, I've got 160 amps MMA varstroj 20+ years old, it has burned down tons of electrodes and only thing I had to replace is main on/off switch, it's definitely worth reparing it. My vote goes to sticking contactor too.

 

[chrisbond]

Thank you Mr Kraft (and chooowie),

It was indeed the contactor (the one at the rear of the unit), which was sticking.

I had it apart last night to check it/clean it and other than some sticky residue on the electro-magnet mating surface and 2 of the contacts needing cleaning (clearly getting hot but not burnt), it seemed OK. I put it back together and re-fitted it and it now seems OK, although I've not tried welding yet (ran out of time last night).

I'll try some welds tonight to see for sure. If it is OK - do you think I should replace the resistor.

Chris.

 

[R Kraft]

The resistor drains the capacitor, so that the wire tip doesn't maintain a charge after the trigger is released, it's sort of optional.
With the contactor sticking it was getting hotter than normal.
If the welder acts ok and the resistor will stay soldered, I would only replace it if you want to for some reason.
Robert

 

[chrisbond]

Test welds completed last nights and all seems OK (better than normal in fact).

Thanks very much for you help Robert.

It was much appreciated.

Chris.

 

[R Kraft]

You're very welcome.
It's good to hear feedback on the advice we give.
Robert