Tig Welder trouble shooting

[cuslog]

Miller Econo-Tig - about 20 years old, hasn't seen that much use (Hobby shop).
Arc not wanting to start - has an arc starter, sometimes that's all you get is the little arc from the arc starter - like you do if you forget to attach (or knock off) your ground. Sometimes arc seems to start from up inside the cup. Will start an arc if you "scratch start" or if you really "nail" the foot pedal but not really conducive to fine work and not how its "always" worked. Acted like this once before a few years ago and I "fixed it" by cleaning up the ground clamp and where the cable attaches to the clamp. Done the same again but no joy this time. Tried a different collet - no joy.
Any other ideas ?
TIA

 

[RobinHood]

Corrosion inside the pedal contacts?

 

[cuslog]

Corrosion inside the pedal contacts?

Well, I thought that was "it", there was a heavy graphite (I assume) deposit from the brush on the coils, sprayed with contact cleaner, wiped it off but no still the same.
Changed to another tungsten and away we go - back to normal - never had a bad tungsten before. The "bad one" was a 1/16" pure tungsten, the one I changed to was a well used (nearly used up) 3/32" 2% thoriated. The 1/16" pure seemed to have a bit of a curve or bend to it, wondering if it might just be a poor fit (poor contact) in the collet- I have used pure before with no problem. Don't know but that's a new one on me.

 

[CalgaryPT]

Might try the tungsten in a different collet from a different batch again. I know you said you tested it but this same scenario happened to me once. Puzzled me for days. Tried two different collets, then had a thought and went back to the old used Miller collet that I had replaced years ago with a pack of shiney new aftermarket brands. Bam...problem disappeared.

So even if you tried a new collet, they may be all from the same batch. I have read posts when aftermarket collets turned out to be copper plated, not solid copper. Even genuine Miller MIG tips occasionally suffer from quality control issues.

Food for thought. Best of luck.