Newbie help with an AC-225-S

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Hello all.  Tried to do a little searching for this answer, but I guess I'm so green I can't even get the search terms correct.  I've had this 225 for over 20 years, and when called upon, managed to spit and splatter enough metal at the joint in question to get by, but I would never even remotely attempt to call it welding.  This week, since a welding pro owed me a favor, I said "enough is enough".  Either learn how to use this thing, or pitch it.  He started the lesson with my old stock that I learned was 6013 5/64" at 90 amps on a 3/4" plate.  Not long after he struck the arc, he declared that my box had a problem.  The current was apparently fluctuating up and down intermittently.  During the running of the bead, he pointed out the sound of the transformer thumping sporadically as if there was a loose connection.  We were running the box on a 30A breaker fed with 8 ga.  After getting the panels off, all the connections looked clean and tight.  While the tap switch didn't look factory pristine, I wouldn't call the contacts dirty or burnt.  Cable connections at the stinger and ground clamp also looked good.  As most of you know, this box is pure simplicity.  Power switch, transformer, tap switch, and a fan.  I realize at 90 amps, it doesn't take much of a bad connection to cause a lot of problems, but shy of an internal transformer short that I can't see, I'm kind of scratching my head on this one.  Would appreciate your thoughts.
Reply:Originally Posted by atty  We were running the box on a 30A breaker fed with 8 ga.
Reply:I would check over the connections again and make sure every thing is clean and tight. If it is this old it wouldn't hurt to take them lose , clean them, and then reconnect. Do this on the input side of the transformer and the out put out to the stinger and work clamp. Work you tap switch back and forth to make sure it wipes itself clean and makes good contact. It this doesn;t work you are going to need a multi meter to make some resistance checks.I don't think you have a transformer problem - they either short or open. If it was open it wouldn't do anything and if it was shorted ( especially if the short were near the middle of the winding where it would decrease the inductance to the max ) you would smell somthing burning and see smoke. If cleaning the connections doesn't fix it ( clean and tighten at the tap switch if you can )the multi meter is the next step. It would be nice if you can get it working since because of its age, it is probably better than a new one.Be sure to unplug it before you go poking around inside. If you get it fixed I would change to a 50 apm breaker but at 90 amps the 30 amp should hold it, but 90 amps sounds a little light for that size rod, but maybe that is just me. Unless I see a lot of spatter and smoke I don't think I am doing anything
Reply:Thanks guys.  I decided to do it all.  Changed the breaker to 50A.  Took apart a few connections, shined them up, cinched them tight, and did a little general housekeeping.At least now I am able to occasionally lay down a bead that is halfway respectable.  More so with 6013, of course.  I have been commanded to stay on 6011 until I get more experience.  Boot camp restriction.  I am relieved to see that it is not apparently a transformer issue and that this box has a lot of life left.  Now on to working my way off restriction.   Thanks again for all the help.
Reply:Artty, what is the condition of the ON-OFF switch? Anything that is going to cause a power loss is going to get hot. At work we look for bad circuit breakers in a panel by taking there temperature. Now welders do get hot, look for things that are hot where unexpected.
Reply:It sounds like he fixed it. I am just waiting now to see some pics of his first project.
Reply:Good point, Transit.  Hadn't really considered that as a trouble spot.  I suppose I could keep an eye on it with a laser thermometer.  6010, that may be a while.  Just got back from another lesson today.  This one on MIG.  Biggest lesson I've learned so far is, no matter how hot it is outside, don't wear shorts.  I forgot how painful a good "sunburn" is.
Reply:If we can't see a project then we need to see some beads
Reply:Well....I suppose it's mandatory to the membership initiation process to post your dirty laundry, so here's my first plate of shame.  Go easy on the Newb.....he's old.
Reply:Go easy on the Newb.....he's old.
Reply:Well......there's a good possibility somebody may have cleaned those sticks off before taking the picture.