Problem with Lincoln Power Mig 200

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I have a Lincoln Electric Power Mig 200 and I managed to get the frame of the welder touching the piece I was welding and I noticed it started to weld about half the time as though maybe half the rectifier went out. It welds, but it spatters a lot and the wire jerks as though it burns and then goes cold so it pushes back on the torch and then it burns again - if that makes since. I have pulled up the parts list and wiring diagram and I guess I will try it again tomorrow and then try to check the diodes. Does anyone here think I am on the right track or should I be looking for something else?By the way, I am new to this forum and I found it as I was trying to research this problem.  Thanks for any assistance anyone can offer.TkingDenver
Reply:hello TKingBefore you pull the covers off. Unplug the welder. Use an ohm meter and check between the drive housing and the case for a short. There may be a piece of wire or something else connecting the drive assemble to the case.  Check the drive motor shaft and make sure it is not broken. They have been know to. If it is broken, the shaft is available from Lincoln as a repair part. It is listed at the bottom of the parts page. Ask and I will post it. Then pull the covers and check the diode and the capacitor bank. Any chance it is still in warranty?  Post the first 5 numbers after the letter in the serial number. (U10805xxxx)  And  the code number I will be able to tell.Checked the parts book and the diode assembly appears to be plates with pressed in diodes. This is sold as a complete assembly.
Reply:ccawgc,Thank you for the reply.This morning I started checking it to see if I could understand what is going on.  I prepped a large piece of steel by grinding a good bare metal place for the ground and for test welding.  I then opened up the wire side and observed as I pulled the trigger and then checked the rollers for anything out of the ordinary.  Everything appeared to function properly and smoothly.  I then took a long piece of wood in one hand and lightly pressed against the end of the wire as I depressed the trigger with the other.  The feed was nice and smooth with no jumping.After the above I tried the welding again and the same results.  The starting and stopping sure seems to be very regular and I am guessing 60hz.  The wire feed appears to run continuous, but the the torch jumps around because during the part of the cycle it welds the wire feeds and melts, but when the arc goes out the wire doesn't melt and instead pushes against the piece being welded thus pushing the torch away from the work. (Hope that describes it.)  I also changed the heat setting and wire feed rate with no change in results.I pulled the covers off and looked everything over and could not see any problems.  Everything is nice and clean and no burned connectors anywhere.  I checked the voltage from ground to each hot lead and also across leads at the power cord connectors and at the input of the switch and also its output going to the transformer.  Everything seemed as it should be.  It is running on 220v single phase.I looked over the diodes as well as possible without taking anything apart and I could not see anything that looked suspect.  I am scratching my head now trying to think if I am missing something.  I guess the next thing to do is remove the rectifier bridge assembly and try to test it to see if any of the diodes are not working.You mention the checking the capacitor bank and I am not sure how to do that, but I will try to figure it out.I have had this unit for 6 to 8 years so it is out of warranty based on a 3 year warranty period.The serial number is K1766-1  10564.Thanks for your help and any ideas.Tking
Reply:After doing some more head scratching, I took a look at the control p.c. board and I am of the opinion that it was probably much more likely to be damaged than the rectifier diodes.  Other than the board, the rest of the "heavy" circuits seem very simple, but the board apparently is responsible for the nice starting and welding, so I am thinking I need to look at that area too.If I don't see something obvious I think I am going to have to haul it to the shop and really be at the mercy of the big money guys.Tking
Reply:Hi the cap bank is the two large red cylinders next to the diode plates.Just look for leaking fluid, fish smell and burnt connections. you will need a cap testerto check the caps.The weld out put is controlled by the voltage switch and the contactor.The pc board runs the drive motor. so if the wire feed speed is constant.The board may be good. Check the contactor and make sure it is not worn out.machines of your age could have a worn out contactor. I it is in the box next to the pc board and drive motor. contacts get burnt, pitted and worn away.It almost sounds like you have an open diode. A shorted diode would make the transformerhum real loud. Make sure the wire does feed easy through the gun. The drive motor current  is measured by the pc board and will stop the welder from working. It tries to protect the motor and pc board from burning up because of a damaged liner.  If you clear all the weld circuits and see a motor speed problem send me a pm I might be able to get you a set of test for the pcb.
Reply:ccawgc,Thank you very much for your reply and explanation.  I am not very good with electronics.  What you say makes a lot of sense because the way I read the circuit I couldn't see any feedback whatsoever in the circuit beyond the contactor.I have looked at the capacitors and they look almost new with no leaks or burn marks, so I think I will have another look at the wire speed and be sure it seems to function right and then pull the diode assembly out to try to test it.  I have not noticed a difference in the sound of the transformer so I think I will be looking for an open diode.  The welder hasn't had much use and I think the contactor is probably ok, but I might try to listen to it while someone else tries to weld to see if I hear it making odd noises.  I think I would have noticed it already just because it is pretty noticeable whenever I pull the trigger.  If the capacitors prove out I will pull the capacitors and have someone check them for me.It is really a shame that the capacitors can't be replaced individually because the complete bridge is listed at about $400.  I seldom use my welder, but I absolutely love it and it makes me sick that I messed it up.Thank you again for your assistance.  I really do not know where I would have been able to find the information you have provided.  I will let you know what I find out tomorrow or the next day.Tking
Reply:the capacitors can be replaced one at a time. but it is best to replace both.there is an easy way to test the caps, if you have a variable DC power supplyand two meters. one to measure volts the other to measure amps..The idea is to charge up the cap, to its rated voltage and watch the ampsdrop top zero. then remove the power supply and see how long the cap, will hold voltage. this tests the internal insulation. if you get current after charging the cap is bad.if the cap discharges like a gas pump with only the meter connected, it is bad.WARNING DO NOT SHORT OUT THE CHARGED CAP. YOU CAN DAMAGE IT AND BURN OR HURT YOURSELF. USE A RESISTOR ON SOME WIRES WITH CLIPS TO SAFELYDISCHARGE THEM. 500 TO 1500 OHMS. Electrolytic caps can be hard to test.
Reply:ccawgc,I like to stay away from capacitors.  I still remember what those harmless looking little things were capable of way back in high school, and these are big ones.  I noticed on the diagram that they do have a resistor across them and that I can also short the ground to the plus side to be sure they are uncharged before I mess with them.  Unfortunately, I will be limited to only being able to check them for continuity unless I take them to someone.I am still guessing a dead and open diode is the problem.  I had emailed Lincoln about the problem and they responded asking me to call.  They put me through to one of their trouble shooters and he said it sounded more like a bad/intermittent ground to him and that a rectifier would result in transformer noise and heat.  Thinking about it now, he was probably recalling experiences where diodes turned into shorts when they failed.  I guess I am now going to go pull the rectifier bridge and see if I can isolate each leg to test for bad diodes.Is there a good source for Lincoln parts or should I just go to any of the businesses shown as Lincoln service distributors?Thanks again for your advice and support.Tking
Reply:If you don't feel safe around the caps. you are best to stay away. do your ohm test.As for parts there are a few along places. It may be best to find a local welding store that can order parts.If you are not in to big  a hurry for the part. maybe you can try to share freightwith somebody elses order.Good luck
Reply:ccawgc & others,I finally got back to my welder problem and disconnected the 4 leads to the bridge rectifier and then put a small 12 volt battery float charger (13.20v) across the ac input terminals and measured a positive 12.77v on the output side.  When I swapped the charger leads on the input terminals I again measured the same 12.77v.  Based upon this, I assume that the rectifier is ok.  Is this a reliable means of testing the rectifier?  The rectifier appears to have 8 diodes pressed in to each of 4 aluminum plates.  I have not attempted to test the capacitors yet.Assuming that the rectifier is ok, or at least waiting for someone to tell me I didn't do an appropriate test, I decided to have a good look at the gun and feed.  The gun is a Lincoln Magnum 250L.  Nothing appears out of the normal, but I had noticed a recent tendency for wire feed slippage when I had tighter bends in the cable.  When attempting to remove the nozzle, I found that it doesn't want to unscrew from the gas diffuser and instead by twisting it, it unscrews the diffuser from the gun tube assembly until it is hanging by the liner.  I can't seem to get a good bite on the diffuser with pliers sufficient to break loose the nozzle without concern for buggering up the diffuser threads.  I can't see that this has anything to do with my welder's welding problem, but I would like to take the entire gun and cable apart to make sure everything is ok and clean before I move on.  Any ideas?Any input or ideas of any sorts are appreciated.tkingDenver
Reply:Problem Solved !After checking out the wiring to the extent that I could, I finally totally disassembled the gun, liner, etc. and did a full cleaning and then tested everything for smooth feeding.  A quick test shows the welder is once again making a beautiful weld without problems.I am going to order a new liner and some more tips and diffuser and nozzle to put it in new condition and keep it that way.  I think I really suspected worse things when I should have looked at the obvious and basic maintenance things first.Thanks for all the help and for this forum.
Reply:Its usually that way.Always check the simplest things first!Every time I hear of someone tearing into something thinking the worst, I think back to my teens and a friend of mine that spent a week trying to figure out why his 73 camaro was missing bad and loping, he told me he first checked it for fire, and it seemed fine, he then replaced the fuel pump thinking it wasn't getting enough fuel, nope not it, he then rebuilt the carb, didn't fix it, he called me and I came over to lend a hand and he started to tear it all apart and take the heads off when I noticed a spark plug wire he had ran through and under the bracket that holds the throttle cable, pulled the wire and there it was, the metal of the bracket had eaten a spot into the wire and was shorting it out, when he did his spark test, he had to raise the wire up which pushed the wire away from the metal and it fired fine, but after putting the wire back on the plug, it pulled the wire against the metal again!I'll never forget the look on his face! #1. If you don't like what I wrote, or if it offends you, then don't read it!#2. I am living life the way I see fit, if you don't like the way I'M living, tough sh**!
Reply:Those are classic "D'oh!" moments!!!I have a few of my own. Like Duane and his wire feeder solution........I am dumb.Lincoln Power Mig 210MP MIGLincoln Power Mig 350MP - MIG and Push-PullLincoln TIG 300-300Lincoln Hobby-Weld 110v  Thanks JLAMESCK TIG TORCH, gas diffuser, pyrex cupThermal Dynamics Cutmaster 101My brain