Welding Tips and Tricks

Hello,
First post on this forum. My friend has an old (1984/85) Lincoln TIG 300/300 AC/DC transformer machine that was bought from an auction, so history and condition was unknown. Problem is the arc formation and I'll try to describe it as well as I can as well as attach 2 pictures of AC aluminum welding and DC- carbon steel welding. Physical contact had be made to initiate arc even with spark start turned on and at least audibly working, it would only maintain arc within less than 1 mm gap between electrode and work piece and changing the power had no effect on this distance. When in AC it sounded wrong (I've used other machines of this era and newer so I know what AC welding should sound like) To me this sounded as if only half of the current was going through and "pulsing" over a gap, like hitting it with +, nothing, +, nothing... In my pictures it also looks as if gas was off, it wasn't. And at times the arc appeared to be coming from deep in the cup rather than out of the tip of the electrode. We cut the grimey end off the ground lead and sanded the ground clamp to ensure a good connection. Any recommendations on where to begin the search for the issue would be greatly appreciated.

It seems that it can be isolated to the high frequency start circuit. Before you go down that path, grab the right manual and check off a few more basic items.

https://www.lincolnelectric.com/en-us/s ... 0300%2F300

Inspect and set spark gap. If points are badly pitted, you can clean them. As someone suggested here, I chucked them in a drill press and touch off on fine sandpaper or stone. Try welding with an AC stick to ensure that the AC mode is working well. HF can be picky of the condition of everything. Closely inspect leads, collet, torch head, internal/external front panel connectors. All of it should be tight, clean, known good another machine, decent quality, etc. It is easy to overlook the obvious when the stuff isn't our own.
I picked a random manual for this information. All large capacitors need to read 0V across terminals and mains power disconnected before you stick your hand in there. Any of the components in the pictured schematic section and timer board can be a potential problem. Check capacitor C4 for any leaking or swelling. Check the electrolytic capacitors on the board for the same. Do an overall check for anything that looks charred or out of place on both sides the board and items posted in schematic. Clean or re-seat connections where possible. Check wiring sheaths for damage, poor repair jobs, corrosion, etc.

Item "D" on the list is a problem that I located in my Miller machine. I went in at night, turned the flashlight off, hit the remote pedal, and found a nice blue spark points leak to chassis ground. I looked down the leads, and everywhere else inside and outside of the welder to make sure this is completely resolved.

Thank you, that gives us a good direction to start in.