Idealarc 300/300 welds only in highest setting

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I have one of those old Lincoln Idealarc Welders that is not working like it should. It is a model: TIG-300/300, Code: 5319-CHP, Serial: AC-192640. I have been using it to weld aluminum with an air cooled torch using argon and a pure Tungsten tip. It has been working very well until just recently something happened. As I remember I noticed the arc started getting weaker and I couldn’t get the metal hot enough anymore. Soon the arc just kind of weakly jumped around without much heat at all. Finally I couldn’t even get an arc unless I would scratch the metal. If I switch to the very highest heat setting I can get enough heat to weld on thin aluminum. I tried to weld in the stick mode and it acts the same way. Doesn't make any difference whether it's in AC, DC- or DC+. I have to put it to the highest setting before it will weld at all. I have tried every setting to see if it makes a difference and like I said only in the highest heat setting can I weld at all, either in the normal mode or HF mode. I have looked under the hood but can’t see anything burned. There is no circuit board that I can see. It looks ancient but I sure would like to get more mileage out of this machine. Any input would be very much appreciated.
Reply:circuit boards under top louvers on the front or check the point gap {hi freq}you can download a manual from lincolnLast edited by prop-doctor; 11-20-2010 at 11:33 PM.idealarc 250/250 ac-dc tigidealarc 250/250 ac-dc tig #2 used for sticklincoln sp100hh125dual arbor grinder polisher30 yrs of hand tools52 pitch blocks 6p-26prake gauge -pitch gaugeG&D prop repair 918-207-6938Hulbert,okla 74441
Reply:I have checked the point gap and they were at the recommended .010". The spark looks and sounds normal when I have it in HF mode. I will look again for the circuit board. Thanks for taking the time to comment!
Reply:Does your remote control have one plug or two.The welders with 2 plugs do not have a pc board, the full reactor current goes through the foot control. 5 to 10 amps. The 5 pin single plug units have a pcb. right side in the back.PCB units can use any current foot control. The older one can'tIf you can't read the diagram on the inside of the right side panel you will have to call Lincoln and ask for a new one. The owners manual does not have one. When you contact Lincoln ask for the trouble shooting guide also. It will help.
Reply:Originally Posted by prop-doctorcircuit boards under top louvers on the front or check the point gap {hi freq}you can download a manual from lincoln
Reply:Originally Posted by ccawgcDoes your remote control have one plug or two.The welders with 2 plugs do not have a pc board, the full reactor current goes through the foot control. 5 to 10 amps. The 5 pin single plug units have a pcb. right side in the back.PCB units can use any current foot control. The older one can'tIf you can't read the diagram on the inside of the right side panel you will have to call Lincoln and ask for a new one. The owners manual does not have one. When you contact Lincoln ask for the trouble shooting guide also. It will help.
Reply:Well, I am hoping that I might be on to something. In the IM-243-A Operating Manual under "Troubleshooting" I found the following: "Machine welds only on maximum. No control." Points to a problem with the AC mag-amp coil. I did some testing on it and sure enough there is an open in the circuit that connects to the Current Control rheostat. Now my question is: Have any of you out there run into a mag-amp coil problem? Are they still available? If not, could they be rebuilt?
Reply:I would look real hard at the wiring before I even think about the mag amp.check the switch beside the remote plug. front panel control and all the connections in this circuit. the remote switch must be in remote off or panel control to work with out a remote control. Look for the 30 volt DC power supply that feeds the mag amp control circuitsThe whole circuit is quite simple, AC voltage turned to DC by bridge diode and fed to the command winding of the mag amp through the panel control. and remote on/off switch.The bridge diode could be shorted out, bad switch contact and ect.Find the panel control on the diagram and work your way back to the bridge diode and aux transformer winding and check every thing along the wayYou can check the mag amp command winding with an ohm meter. Look for low ohms but not zero. THe bridge diode may be a finned assembly that is a selenium based diode.Silicon bridge diodes are a black block. They work and test the same.In all the units I have worked on none have had a bad mag amp. Most of the time it is little things, Had one with a blown main transformer. There are two types reactors used in welders. One is the mag amp and the other is a saturable reactor. both work the same but the mag amp goes max output with out control voltage and the saturable reactor goes to minimum.