problems with used idealarc 250

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i recently got a used idealarc 250 roundtop, it looks like it was well taking care of.  i reworked the cords, new quikconnects, stinger. when i run the welder on ac, seems to work fine, but dc+ is really rough that it wont weld and dc- trips the breaker. its on a 40 amp breaker, using 1/8 rod at about 90-100amp. Also the ground clamp starts getting warm after a few minutes when i tried it out today. i am novice at welding at best, so any help would be great.Last edited by Chap3l; 10-25-2011 at 08:06 PM.
Reply:You've most likely got a shorted rectifier in there. On AC, the rectifier stack is out of the circuit. Post the serial and code number of the machine so we can figure out which variant you have. Lincoln made some changes to the diode stack over the years. Mine has 4 large ones, others have more, but they are smaller and work in parallel to handle the current load.PapaLincoln Idealarc 250 (circa 1962)Lincoln Weldpak 155 w/Mig KitLincoln Squarewave TIG 175
Reply:Diodes are in circuit all the time, Pull the top and look at the polarity switch. My guess is it is falling apart and is burnt. or the switch has been replaced and has been wired wrong.Diagram is in the owner's manual. Down load from Lincoln and check it out. Might have a readable diagram inside the cover.
Reply:thanks for the replies, i took it back to the guy i bought it from and his service guy said it had a short on the switch. fixed the short and works great.