Hi,

I am a beginning TIG welder. I have experience with stick and wire. I was given an old Airco Heliwelder IV. It is the 300A version with a water cooled torch and foot switch/amperage control. The code is 0665, the serial is MH10190, and the stock is 1341-0176.

The HF, the footswitch start, and the post flow all work fine. The problem with the system is in the amperage control. The output is the maximum of whatever range is selected (low-med-high). This is true for both the panel setting as well as the foot control. Both the panel potentiometer as well as the footswitch potentiometer feed into a PC board which the block diagram on the panel schematic calls a "Reactor Board". I shot gunned all the high amp parts, the thyrister and bridge rectifier and a couple of transistors. I then sent the whole reactor assembly to a company who repairs obsolete equipment. I labeled all of the connections before I sent it out. When it was repaired and sent back there were wires terminated differently than when I sent it to them. The board had tell-tale signs of previous repair before I sent it out. I am now unsure if the thing was connected properly as I was troubleshooting it. The block diagram is not detailed to the point that I could tell how to connect; there is a vacant terminal on the PC and a extra wire. I do not want to cook the $300 PC or anything else for that matter.

Does anybody have an old Heliwelder who could help me out with some wisdom or pictures or advice??

Sorry for the long intro, I have been tinkering with this for some time. Thanks in advance to anyone stepping up!

Lou