1. Airco Heliwelder Manual

Assuming you are very familiar with its operation and know if is not working right, you might be into troubleshooting the internals of the unit. Could be a number of things, but I would consider the old selenium rectifiers in the output stage that senses open circuit and welding voltage to trigger the timers and relays. Does the post flow timer work properly after breaking arc? I have an airco HF unit, and they might be similar in that it uses the voltage out to sense whether you have struck an arc or not. It does this by rectifying the output and chanelling it into a relay and timer.

A drop in voltage when on the DC setting, tells the unit you have struck an arc. It then starts the timer that kills the HF.

If your machine is vintage, it probably has selenium rectifiers (used to see them in the old tv's. They look like the diagram for a battery, in that they have a series of small (maybe 1' square) heat sink plates parallel to each other).

They don't last forever. You would have to disconnect one side of each and test them with a multimeter for proper diode action. Ie, they conduct one way, but not the other. They can be replaced with modern rectifiers. You might be able to get a schematic from Miller as they are affiliates and some of the equipment appears to be the same, just labled differently as to brand name.

You might be able to get a schematic from Miller as they are affiliates and some of the equipment appears to be the same, just labled differently as to brand name Am I correct in assuming that Miller took over Airco? I have an Airco Bumblebee stick welding power source circa 1975 that I seldom use but still works real well. This is BIG size machine like would be used in a shop setting. I fell into a deal I couldn't pass up on a few years ago and rolled it home.

Just wondering. Thanks for any input! Bullseye Timinmb, U da man! I think you hit it dead on. We were looking at the scematic and wondering how that part of the circuit works. We'll check the rectifiers today and I let you know for shure if we have a bad one.

The post flow works fine. You mention a timer that kills the HF, I don't see one in the schematic. Do you know what sets the 'level' or point that the HF goes away? I have an older one (heliwelder300) at home too.

On it, when I let off the pedal to the point that the arc drops out it goes out. On the one we are talking about, the arc drops back to that funky spark plug looking HF arc when I go light on the pedal!!! Shouldn't the circuit latch so that it does not go to HF on the down from an arc??? Originally posted by jasowiii Timinmb, U da man! I think you hit it dead on. We were looking at the scematic and wondering how that part of the circuit works.

We'll check the rectifiers today and I let you know for shure if we have a bad one. The post flow works fine.

You mention a timer that kills the HF, I don't see one in the schematic. Do you know what sets the 'level' or point that the HF goes away? I have an older one (heliwelder300) at home too. Sql lab manual. On it, when I let off the pedal to the point that the arc drops out it goes out. On the one we are talking about, the arc drops back to that funky spark plug looking HF arc when I go light on the pedal!!!

Shouldn't the circuit latch so that it does not go to HF on the down from an arc??? Jimmy There's lilkely a number of different ways these things have been built. But on the schematic I am looking at, the timer is labeld 'TD' in a circle on the schematic. Relays are labeled 'CR' in a circle. The contacts for the timer (TD) or relays (CR) are indicated exactly like a (non-polarized) capacitor, two parallel lines - - (what a confusing way!). If the contacts are normally closed, they will have a diagonal slash thru them.

On my Airco / Miller HF unit, if you set it to AC mode, the gas, water and spark run continously during the welding process, but but stops once the welding arc is broken. This involves both the sensing circuit of the selenium rectifiers and the timer. In DC setting, the timer starts and holds the spark, water and gas flow on for its set time. If you start a welding arc, it kills the HF.

This is once again, a funtion of the selenium rectifiers and CR1, a 24 volt dc DPDT relay. Why the rectifiers? I guess they serve to control the relay regardless of whether you are welding with AC or DC. There is also a resistor to drop the voltage to the relay so that it clicks in or out based on load to the transformer dropping voltage.

I think you need to figure out from your schematic how the foot pedal is tied into the CR that controls the HF transformer, as that seems to be the problem area. I was lucky in that my HF unit has the same part number whether its Airco or Miller, so I was able to get the PDF file for the manual and schematics off the Miller site. Cheers to Miller for posting this (0ld) stuff.

Hopefully this old thread has some life left in it!! 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 seemed to be 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. I do not want to cook the 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??

Airco Heliwelder Manual

Sorry for the long intro, I have been tinkering with this for some time. Thanks in advance to anyone stepping up! Lou, I did some checking and could not find anything on your machine so I ran it by one of our TIG experts and this was his response. 'This unit appears to have been manufactured by someone other than Miller Electric. We have never used a code number, the serial number is not a Miller and the Airco stock number is not in any of our cross references.

The physical description of the internals of the machine are not like anything I am familiar with.' Sorry I could not be of any assistance with this one. Airco 300 AC/DC Heliwelder IV power issues: Hello Lou, I have read your thread and we have similiar problems. I think we can help each other out. I am also in the process of replacing the reactor pwb too. I am questioning the wiring on the 25 amp rectifier that is located above the reactor board. Is the red wire connected to the - side and the black wire connected to the + side on the rectifier on your machine.

I can send you pictures of my welder if you need to see something for comparison. Let me know if I can be any help to you since you and I maybe the only ones left on this planet that have an old Airco Heliwelder 300 IV in our basement.

Also do have a schematic on the reactor pwb circuit that I can look at? 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 seemed to be 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. I do not want to cook the 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!