Hi all... thanks for reading this. I'm wondering of someone has experienced this problem or perhaps has a solution to it. I'm not a welder in any way, so please excuse some of my decriptions below. Since I specialize in electronics, my friend has approached me to check his welding machine out as it has been doing weird things lately. He is using a Lincoln Wirematic 250 welding machine and what happens is that it will lay a nice weld for about 5 or so seconds which will be followed by sputtering, bubbly and a rather ugly weld, this would be followed by a nice weld once again and so on so forth... The sputtering can actually be heard by an untrained ear. There are four filter capacitors that parallel the gun to the ground. All of them check fine on my cap meter at 30,000 microfarads ( I did check them separately). There are also two SCR's that are used to control the output voltage. I checked them and they seem fine, although those have been checked in a low current application - about500 mA, since I had no access to a 150 A source to give them "the real test". All that's left is the transformers, chokes, clamping diode (checked OK), a shunt resistor and a control board. I don't have the schematics for the control board but was able to follow a few traces to see where the control signals are going to and where the current and voltage sampling enter the board for processing. So far the board seems fine but I can't be 100% sure.
Can anyone help me with this? Am I being led down a garden path by looking in the wrong place? Has anyone ever experienced such a problem?
All your replies would be mostly appreciated.
Thank you. Alex