Parker Metal Working TIG not working correctly

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I'm looking for a little help regarding my Parker Metal Working AC/DC Tig 200. A little over a year ago I got this welder from a friend in a non-working condition. I shipped the welder to Parker for repair. A few weeks later the welder arrived back and sat for a month or two. When I unboxed it I played around with some scrap stainless in DC TIG, which worked perfect. I tried to weld some aluminum in AC and it worked great. I welded several aluminum pipes and some practice beads on some 3/8" flat aluminum plate. The welder started to act up so I called the guys at Parker and spoke with Phil Sr. He gave me a whole list of stuff to check/try. I've gone over everthing he asked and the welder still doesn't act right (which I'll explain).While in DC every once and awhile (maybe 1 out of 10) the arc won't start. I'll see the high frequency start-up arc (if that's what it's called) but the welding arc doesn't start. I found that if I scratch the tungsten while this problem persists the welding arc will start.Now the weird one. While in AC, the welding arc won't start if I try to weld aluminum, or even stainless (my workbench top) just to test. This is with the ground connected to the table or direct to the workpiece. If I ground to the table or the vise mounted to the table, I can start an AC arc nearly every time if I have the tungsten starting the arc through the large flat part on the back of the vise which is made of steel. To me, that makes zero sense as to why that should matter. I've welded aluminum many times with an older Miller syncro so I'm aware of how clean aluminum needs to be. What boggles my mind is how the welder will work perfect in AC on thick steel and won't even start an arc on stainless or clean aluminum.Thoughts on what would cause thisThanks!Matt
Reply:You need a clean connection from your ground clamp to work to reliably start the arc.Try and improve the connection - clean the contact surfaces (vigorous scratching on the jaws with a wire brush should do it), increase clamping pressure, etc.Sharpening the tungsten can also help a lot.  The arc will much more readily jump off a sharp point on the end of the tungsten, than a rounded over, melted or "used" point.  And use an appropriate diameter tungsten for the current at which you are trying to start.  (Don't try and start with real low current, with a large diameter, worn out tungsten - it won't work  Use a small diameter, sharpened tungsten instead.  Or, use more amps when starting on your current tungsten.)Aside from those tips, it sounds like parker guy gave you a whole list of things you can check on your machine, so probably don't need internet advice on that.  However, the only item I would think you should be checking inside the machine is high frequency gap.  I'd recommend filing or sanding the gap contacts, to remove all oxides or contamination from the surfaces.  Take them both down to clean copper.  Bend them if needed to make them parallel to each other.  And set an appropriate gap distance.  More info in this thread:http://weldingweb.com/vbb/showthread.php?t=35536
Reply:By any chance are you using pure tungsten electrodes (green band), or some unknown Chinese brand?  Pure tungsten electrodes can give severe arc starting problems with some inverter power supplies.  Check this out and try a reputable brand of electrode such as Sylvania, and use 2% Lananated, Ceriated, or Thoriated.  See this link.  http://www.diamondground.com/index.html
Reply:just sounds to me like your ground clamp is making poor contact.  Maybe the sping is too weak in it, or the pads are dirty.  clean and tighten everything associated with your ground clamp and cable/connectors.
Reply:First off, thanks for all the advice so far. I'll go ahead and list all the things the guys at Parker Metal Working had me do.1.) Open the case and check all visible connections. Tighten anything loose and advise on what I find.--- I opened the case and checked everything and found nothing out of the ordinary. All the nuts, screws and plastic connectors were snug.2.) Modulate the pedal with a volt/ohm meter hooked to check that the resistance goes up and down as the pedal does.--- I did this and provided the readings to Parker, which I was told was normal3.) Try both 2% thoriated and pure tungstens and monitor the results.--- I tried both and didn't notice any difference.4.) Clean all grounding surfaces, then clean them again.--- Tried this literally 10 times overI'm using 100% argon at the moment. Like I said earlier, I was able to weld aluminum a few times with great results before the welder started to act up. I tried a few other things last night before giving up. I attached to grounding clamp to a 3/8" bolt screwed into a compressor housing for a turbo. I then cleaned part of the housing and tried to weld it, no dice. I then laid the compressor housing with the clamp attached onto my stainless workbench. At that point I tried to start an arc on the stainless table, again, no luck. I then moved further down the table and was able to start an arc several times on the back of the vise which is bolted to the table. Very weird.After that I gave up and called a local Miller and Lincoln repair facility. Since I can't get a hold of the guys at Parker (number goes straight to voicemail for days and days) I dropped if off with these local guys. I'll be sure to let you guys know what, if anything, that they find.Thanks!!Matt
Reply:Originally Posted by jakeruYou need a clean connection from your ground clamp to work to reliably start the arc.Try and improve the connection - clean the contact surfaces (vigorous scratching on the jaws with a wire brush should do it), increase clamping pressure, etc.Sharpening the tungsten can also help a lot.  The arc will much more readily jump off a sharp point on the end of the tungsten, than a rounded over, melted or "used" point.  And use an appropriate diameter tungsten for the current at which you are trying to start.  (Don't try and start with real low current, with a large diameter, worn out tungsten - it won't work  Use a small diameter, sharpened tungsten instead.  Or, use more amps when starting on your current tungsten.)Aside from those tips, it sounds like parker guy gave you a whole list of things you can check on your machine, so probably don't need internet advice on that.  However, the only item I would think you should be checking inside the machine is high frequency gap.  I'd recommend filing or sanding the gap contacts, to remove all oxides or contamination from the surfaces.  Take them both down to clean copper.  Bend them if needed to make them parallel to each other.  And set an appropriate gap distance.  More info in this thread:http://weldingweb.com/vbb/showthread.php?t=35536