Airco High frequency issues

[Osar]

I have a 1961 Airco Heliwelder. 4A/DDR 224/HPA/B-D. High frequency works ok for DC TIG, but stops working after a few seconds on AC continuous. Hoping somebody can start me off in the right direction here. I have the operating and maintenance manual for it.

[Osar]

Airco High frequency issues

Anyone?

[NHTIG]

Anyone?

I am not familiar with that particular machine, however I believe most HF circuits of that era operated in a similar manner. I assume you have a switch for HF that has the Off, continuous and start functions. When you have it in the "start" mode HF starts and then quits when the torch lights?? I would make sure it quits by verifying no "arc" at the point gaps when the torch lights. Old machines can have all kinds of "history", meaning they have been sometimes played with a LOT internally over the years. IF the above is all true I would look at the HF switch as a strong possibility. OR possibly clean the HF intensity control. If you punch the pedal (assuming you are using one) without lighting the torch you should see a constant spark across the spark gaps. If this is true in the "start" mode the only difference really is that switch. In the "start" mode the control circuit sees Open Circuit Voltage until you establish an arc. When you establish the arc the control circuit "sees" the change in voltage and usually (in older machines) pulls a relay that shuts off HF. So I would first check the switch, clean the intensity control, check wiring connections to make sure they are secure and then I would probably try to get a tech manual and verify the wiring. HOPE some of this helps.

[Osar]

Airco High frequency issues

Thanks, I'll check it out. Perhaps I'll have someone watch the relay too, while I'm welding. Actually in HF start mode, you get about 1 second of HF on this machine.

[NHTIG]

Thanks, I'll check it out. Perhaps I'll have someone watch the relay too, while I'm welding. Actually in HF start mode, you get about 1 second of HF on this machine.

HF should function continuously in the start mode until you strike an arc. The machine does not know it is in start mode until it "sees" a voltage change at the output (arc being struck) then the control circuit takes over and drops HF. If this is not true then perhaps you have an HF capacitor that breaks down and shorts after that one second period. The machine probably has two HF caps. If it does disconnect one and try it. If this does not work reconnect that one and connect the other and try it. If one is shorting the one left in the circuit SHOULD function well enuff to give you a weaker spark BUT the problem may go away. Of course this would mean you need new caps. Good luck and have fun. I have been doing this stuff for years and still enjoy "the chase". There are lots of possibilities here, just takes time to sort things out. Let me know. Perhaps I can find a schematic of this machine and be able to help more.

[H80N]

Believe that to be the same as one of the Miller 330 ABP variants...(OEM Version)
similar to this one..

http://www.millerwelds.com/om/o340_mil.pdf

I would just clean out the HF section and look for carbon tracking and HF leakage...

these are pretty basic machines without much control circuitry..

a good cleanup and regap of the spark gaps should help too...

in a shop environment after many years..these machines collect a lot of conductive dust and grindings..
they are built like a tank.. but even a tank needs some periodic maintenance..

[NHTIG]

Believe that to be the same as one of the Miller 330 ABP variants...(OEM Version)
similar to this one..

http://www.millerwelds.com/om/o340_mil.pdf

I would just clean out the HF section and look for carbon tracking and HF leakage...

these are pretty basic machines without much control circuitry..

a good cleanup and regap of the spark gaps should help too...

in a shop environment after many years..these machines collect a lot of conductive dust and grindings..
they are built like a tank.. but even a tank needs some periodic maintenance..

Osar...any news on this???