AC/DC TIG machine stuck on DC?

[andrewmacc]

Hey folks,
long time viewer of the forum, just without an account.

Now I know the general opinion of brands like Everlast, but I'm hoping somebody could help me troubleshoot this darn thing.

The machine is an Everlast AC/DC TIG 200DX. It's at least 7 years old, as some of the components inside the machine had some stickers on them with the date of "2012".
I've actually been fairly fond of the machine other than the horrendously bulky and stiff 26-series torch that comes with it.

I've welded aluminum with it in the past, so I know how the machine should be operating and sounding.
But when I switch the machine to AC and try to weld aluminum, it's just a gong show and acts like it's only welding on DC.

Okay, so:
* It still works fine on steel on DC.
* When you switch to AC, something is registering as you can see the digital amps display change the amps due to the different ranges between AC and DC.
* HF start always works. Functions as expected, is audible, and when I took the cover off, can visually see the arc jumping the gap.
* Changing the frequency or balance does nothing. It just sounds identical to DC welding. No buzz, no nothing.
* No change if I use lift arc.
* No change if I play around with pulse etc - pulse works fine, just still no AC buzz.
* Gas is good - like mentioned, no issue on steel.
* I traced the wires going from the AC switch as much as I could, didn't see any resistors or caps that let the smoke out..


Any clues? Of course I bought a bunch of aluminum for a project and now I can't even tack it together!

[shovelon]

Bad switch?

[ccawgc]

Most likely one of the IGBT switch units is shorted and you are stuck in DC.
If it was a miller I look for a polarity change from DC tig to DC stick. HF has to be turned off.
Most inverter TIG units with AC have a IGBT module that switches the polarity. one turns on for DC-
the other for DC+. both turn on alternating to make AC. your unit should be similar.

[lugweld]

Check just behind the front board, between it and the main board, a little to the left (facing the front of the machine). There is a plug that goes to the main board the comes up that has several wires to it that controls the AC among other things. Try reseating it. It can get loose on those older machines IIRC. If not, just give our tech support department a call. Tech support is free. 9 to 5 eastern. 877 755 9353 ext 207

[andrewmacc]

Bad switch?

I was trying to figure that out too. The switch is switching something, because you can see the display panel change the amperes setting.

Most likely one of the IGBT switch units is shorted and you are stuck in DC.
If it was a miller I look for a polarity change from DC tig to DC stick. HF has to be turned off.
Most inverter TIG units with AC have a IGBT module that switches the polarity. one turns on for DC-
the other for DC+. both turn on alternating to make AC. your unit should be similar.

Interesting! So turn off HF, pull out the multimeter and would I be testing DC voltage between ground and power and see if it's switching polarity (+ to -) between modes?

Check just behind the front board, between it and the main board, a little to the left (facing the front of the machine). There is a plug that goes to the main board the comes up that has several wires to it that controls the AC among other things. Try reseating it. It can get loose on those older machines IIRC. If not, just give our tech support department a call. Tech support is free. 9 to 5 eastern. 877 755 9353 ext 207

Will do! Thanks lugweld. I'll check this weekend (my machine and tools are 45min away in another garage.. sigh). If reseating the plug doesn't work, would your opinion start aligning with ccawgc's about an IGBT switch unit?


Thanks everyone! I quite like the welder, it's very easy to read and operate and has been flawless for years, so it was a shame to switch to AC and manage to melt up some aluminum into a gob before realizing I wasn't hearing the telltale AC buzz - I just keep meaning to replace the torch with a flex torch!

[andrewmacc]

Alright, so..

* Reseated the plug going from the AC switch. Reseated the AC switch spade terminals.
* Tried checking polarity - didn't see any switching. Just got straight polarity when hooked up to the multimeter. OCV was like 70-something volts.
* Tried tracing continuity as much as I could but it's more difficult without any schematics. I could detail that out but it's long-winded and without a ton of conclusive material other than seeming to lose continuity between the large grounding (?) block that has the ground straps going to the board, and the inputs into it. I have some pictures I could doodle on to show that.
* So I tried hooking up a stinger, switched to Stick, and was able to weld DCEP, DCEN, and switched to AC for both, with some 7014... no noticeable differences.

However... after burning 2 rods, and then I was just striking an arc with the third rod, and the welder cut out, turned on the duty cycle light (green LED)... and it's stayed on ever since and I can't get an arc. Tried leaving it on, tried blowing air to help it cool, tried switching on/off, tried unplugging it, even got so ballsy as to touch some of the components and everything was completely cool to the touch.

So that's where I'm at. Didn't even get to re-hook up the TIG torch to see if it's magically been fixed.

[lugweld]

The unit doesn't weld AC in stick mode! If you were trying to weld in TIG mode you could have hurt the unit since TIG is at a lower voltage.

[andrewmacc]

The unit doesn't weld AC in stick mode! If you were trying to weld in TIG mode you could have hurt the unit since TIG is at a lower voltage.

All is well - I only weld stick once I've switched the unit to "Stick". Haven't ever attempted it while it is on any TIG modes.

But that would explain the lack of change when using the switch to go between AC and DC - I wasn't sure as I also have an old AC Lincoln tombstone welder.

I let it sit for quite a while and went back and turned it on. Duty cycle light was off initially but immediately came on when I tried to strike an arc. HF still fires but no arc, and light is back on. Any ideas?

[lugweld]

Just call our guys in tech support. Could be a loose wire somewhere. Ext 207 at 877 755 9353.

[Kelvin]

The unit doesn't weld AC in stick mode! If you were trying to weld in TIG mode you could have hurt the unit since TIG is at a lower voltage.

[lugweld]

Drawing a longer arc length increases the voltage, longer than what TIG is intended for, and can over amp the circuit.

[shovelon]

Drawing a longer arc length increases the voltage, longer than what TIG is intended for, and can over amp the circuit.

That is true. Longer arc increases voltage. But how does a long arc over-amp a circuit? Does that mean faulty engineering? Arc welding regularly uses the break arc technique for extinguishing an arc.

I regularly teach tig workshops by intentionally over lengthening a tig arc AC or DC to demonstrate proper arc length and never pooffed a machine. I have my attendees repeat to get the feel of a proper arc length, so I a very confused.

[lugweld]

Terry,
I was referring to trying to stick weld in TIG mode. It's got everything to do with engineering, not faulty engineering. When you control the input amps as in an inverter, they are designed to cut out if the arc is accidentally broken in that mode when TIG welding. It's a quick snap up. But when stick welding, you are likely going to be running a longer arc constantly, nearing the point of cut out. Doing so repeatedly in that mode is not recommended. Would you drive in first or second gear at the redline for a few hours in a car on the interstate just to say it is faulty engineering if there is an issue? You might, most would not.

[andrewmacc]

Alright, well, after some helpful troubleshooting from Mike over at Everlast, it sounds like it would need non-warranty repair. Current sensor appeared within spec, and overriding the temp sensor didn't do anything either. The guesstimate was around $500 + shipping. And I'm not sure that would fix the original issue which was the lack of AC. They offered a small discount on a new machine but I think I decided to pass.
Over the weekend I picked up an old blue. Pardon the garage, Spring cleaning never actually happened, so maybe it'll have to be a cold Fall cleaning.