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!
Thanks for responding. I have followed your threads for some time now.
I took a leap of faith and made the connection of the extra wire to the only terminal left on the PC board. I now have control of the amperage. However, it is of very low output. On the low and medium ranges it is unable to lay a puddle in 1/8" mild steel. On the high setting, the pedal responds but for a 300 amp machine it seems very weak. I think there is something miss connected on the output, but going from the "block" diagram I cannot proceed any further. I was really happy that I did not let the smoke out of the newly repaired board!
I could still use any help by means of documentation or pictures or advice. I agree with you, it is probably a very simple fix, a five minute modification. I am just at the end of my capabilities with my current resources. There is absolutely no rush. I use the welders to help friends and family. The TIG is learning vehicle. It is not a business, mostly for my own pleasure!
If you are still working on this, I have hundreds of welder service manuals, including one for your machine. I just found this forum or I would have mentioned it sooner. Let me know if you need a copy.
I just came across this website and noticed you replied to another gentlemen regarding his welder. I have an old Airco 300 Heliwelder IV machine with a similar problem of no current control. I have just ordered a new reactor pwb for replacement and apprehensive to power the unit up. I need to know and to verify what color wires go to the 25 Amp bridge rectifier mounted directly above the reactor board. There are four wires; colors are blue, white, red & black. I know the white & blue go to the AC terminals. Would you know the correct wiring for the red & black leads? I have a picture of the wires in question. I would greatly appreciate your comment or any suggestions. What are the possibilities that you may still have a schematic on that particular circuit pwb or the machine?
Thank you much for your time.
With information provided by thedoctor I was able to correctly connect the reactor PCB and verify operations with test points and performance parameters. I sent the PCB to Radwell International and they repaired it. It has returned and the welder seems to be working. I have friend who is an expert TIG welder who will confirm ops for me.