Problem with MIG welder

Does it look anything like this:

STEMCO 430-1154

If so, you should measure a short across the ¼" terminals. It'll be self-resetting (but it might've broken).

Yes, thats it. It does measure a short, but as you say, it might be broken.

If it's a short when cold, there's probably nothing wrong with it. It definitely won't stop the welder starting to work.

Must be something else.

No suggestions at present - sleeping on it.

Here is the service file I have on the Century 117 - 053 model.

Here is part 2 since the editor will not let me put more than one picture on a post now.

Part 3.

Difficult to make out, but this sheet appears to show a thermal cut-out in the line from the top secondary of the transformer.

And part 4.

ronseto;the L175 refers to the temperature that the device opens circuit,they are available at graingers, or other supply house. perry

Your comment is unclear, at best!

Thank you all. I knew I came to the right place.

If you are affirmative that all the transformer secondaries are outputting the correct voltages, then look at the electronics.

To have a DC output, you need some rectifiers, do you know how to test them?

do you know how to test them?

I'm not sure if I can test them in the circuit. My meter (Fluke) says I can test diodes if the parallel resistance is >2K. The resistors read < 2K. That being the case, I would have to remove the SCR's from the board to check them; a whole lot of work.

Unfortunately Century is sort of the ass end of welder power supply manufactures. Their control boards are fairly simple and can usually be fixed by a person with fair electronics knowledge but if you don't have that or know someone who does then changing the control board is by far the most common option.

resolder all of the solder connections and check each component to see if its burned or shows signs of physical heat stress. If that does not do it then you either need a rebuild or a new board.

A new board costs $245. My son checked it out with an in-circuit P-N-P/N-P-N tester and they were all ok. There was an IC that wasn't checked due to lack of specs.

Does that IC have 4 or 6 pins? If so its an optically isolated triac or SCR and they are a common failing point with century boards. One side should show voltage across its two terminals when the trigger is pulled the other side fires the sets of SCR's.

They are about $1 - $2 at most at http://www.digikey.com/.

Dear TCMTECH, Your comment regarding my Century MIG welder was right on. I replaced the IC and the welder has been working fine ever since. Thank you again for your help.

Hello, on most welders that do not have a constantly energized tip there is a heavy duty continuous solenoid in line with the dc output. Have you energized the coil in the solenoid and checked for a connection there? If it is malfunctioning you will have all systems go but no output.

The thermal cut-off is self-resetting. I tripped mine one day and it took a few hours before everything worked again.

These devices do fail so you may need to replace it.

At risk of stating the obvious, have you checked the continuity of the earthing point & cable? I had a problem with my welder (not same make, but..) where everything worked, but no spark. Turned out the crimp at the welder end of the earth cable was not tight enough - tested fine with a meter, but would not take anything like the 50A needed for a spark.

My info may be no help but I had the same kind of problem and found the trouble to be a small relay on the control board. The relay used 24 VDC coil voltage and it's contacts were way undersized for controlling the welding current to the transformer. They were completely destroyed. Was lucky enough to find a replacement on the web.

Good luck

In my post #5 with part four of the service file there is a schematic that shows how the control board is built. In this model the output voltage and current is regulated by 8 big SCR devices.

The odds are your board went bad and is not triggering those devices any longer.

I don't know that brand, but several like to hide a small fuse (like 250mA glass tube type) on the back side of their PCB's. Replace it and generally you're back in business.

I see that you have spent some time checking the unit out. I know that this may sound a little too simplistic, but on some of the Century units, the trigger switch on the gun assembly can go bad without any symptoms or warning. You can use it with no problems one day, then it will not work the next. I would confirm that the switch is working properly.......this little problem has embarrassed me more than once. Number 2 on the embarrassment list is to make sure that the work lead (ground cable and clamp assembly) are getting a good connection and properly grounding............good luck.

How will the wire feed work if the trigger is bad?

In most cases the wire feed will not function at all if the trigger/switch is bad. One point I forgot to mention is that if the gun cable assembly is bad (copper strands fatigued and broken where it connects to gun) it may work erratically, or not at all. Also make sure cable assembly is connected to machine correctly. Like I mentioned in my earlier response, sometimes it is the most simple things getting overlooked that are causing the problem(s).