Lincoln SP-175+ stips breakers......why?

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Hello. I have a Lincoln SP-175 PLUS mig welder that needs some attention. I dont use this welder much maybe twice a year or so, and now it is acting up. The machine doesnt even have wire through it at the moment, but once I pull the trigger the breaker trips. I went up to a 50 AMP breaker and it makes a buzzing/humming sound. What could it be and how do I go about testing it?
Reply:1 of your diodes has shorted,
Reply:Thanx for the reply. As far as I know the diodes are located inside the rectifier. So I need to take apart the rectifier and look for a burnt out diode? What does a bad diode look like?
Reply:Diodes are located on this plate.  It's located opposite the wire feed & you will have to take the cover off to test them.(sorry for the fuzzy pic, hands were shaking) Attached ImagesMarkI haven't always been a nurse........Craftsman 12"x36" LatheEnco G-30B MillHobart Handler 175Lincoln WeldandPower 225 AC/DC G-7 CV/CCAdd a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG PapaLion's Gate Build
Reply:real easy to test. Get a multi-meter with diode test.Unplug welder and remove cover. pcb is attached to cover. turn cover over and put handle in the top of the wire side. Now unplug large multi wire plug from pc board. Then unbolt the transformer strap for the outside heat sink. Aluminum plat the diodes are mounted on.Next unbolt one wire from the large capacitor. Now all the diodes are isolated.The AC part of the bridge diode assembly is the plates. The DC part are the wires on the large cap. check for a short between each of the DC wires and both plates. One set at a time. In diode test mode the meter will read  around 0.400 for a good diode and OL in reverse.Of coarse a shorted one will read 0.000 Your welder should have 8 diodes. 4 pairs. They are using two parallel diodes as one higher current diode.
Reply:I recently took the rectifier out to test the diodes. Visually they all look good with no traces of anything, so I went ahead and scratched brushed the terminals for a better connection. My volt meter doesnt have a diode testing feature in it but I did test for resistance, and all are running between 1.7-1.8 Ohms. Is this an ok way to test?I tested for continuity of both thick black wires going into the red tall cylinder and it tested fine.How do I test the red tall cap to the right? How about the big wounded coils? I hope I get this fixed soon. I have a few jobs to finish.
Reply:Does it look like it's "leaking"?  Or the top/body bulging?  To test, you can use the multi-meter to give it a bit of a charge.  But be very careful, they will jolt you pretty good if you don't discharge it before handling it.MarkI haven't always been a nurse........Craftsman 12"x36" LatheEnco G-30B MillHobart Handler 175Lincoln WeldandPower 225 AC/DC G-7 CV/CCAdd a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG PapaLion's Gate Build
Reply:If you have only 1 to 2 ohms with a standard ohm meter the diode is bad. How old is your welder. if it is less that 3 years old put it back together like it never came apart and take it in for warranty repair. If it is more than 3 but less than 5 call your local lincoln shop and see If they will work with you on a parts only warranty. I am pretty sure the diodes only have a 5 year parts warranty. The diodes in your unit are sold as a complete assembly It is know as the new style diode assembly. The old style had replaceable diodes, 8 of them.The date of sale is when the warranty starts. But you will need your receipt.Date of manufacture is in the serial number. first two is factory and country code next 2 are year and next 2 are month.   U10706XXXXXX   usa plant 1 , 2007 june.
Reply:To test the cap. Check with your ohm meter make sure it is not shorted. The resistance should go up during the test, as it charges up. Also look at the top of it and make sure the plug is not leaking. After welding a while unplug the welder pull the cover and see how hot the cap is. if it to hot to touch we have a problem. other wise it should only just warm. This is about all  you can do. It Takes expensive meters to make any other tests.Last edited by ccawgc; 10-24-2010 at 11:41 PM.
Reply:Resistance goes up on the cap so I guess thats good. Bad news is my welder is lamost 6 years old so warranty goes out the window. Can I buy just the diodes separately or do I have to buy the whole rectifier assembly?
Reply:Lincoln only sells that as a complete assembly.The diodes are pressed into the AL plate.the L number on the sticker should be the part number.I don't know if you could work a alternator diode or 2 into the plate or not..and have it last.
Reply:After a few months of laying around I brought the welder to a local Lincoln dealer. The repair guy told me that it is the board. He wants $385 for it installed. I was very upset at the price and took the welder back. At this point I am confused. The bard looks good and has no burn spots. Also why would the board trip the breaker when you pull the trigger? To me a bad motor or coil would do this to a breaker not the board. Is there anyway to test the board myself?
Reply:Might contact Duane here on the board.  He fixes/refurbishes welders.MarkI haven't always been a nurse........Craftsman 12"x36" LatheEnco G-30B MillHobart Handler 175Lincoln WeldandPower 225 AC/DC G-7 CV/CCAdd a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG PapaLion's Gate Build
Reply:When you tested the diodes, what type of meter  did you use. And did you reverse the leads and measure both directions. A short in one direction and open in the other is a good diode.I just means you meter uses a higher voltage to test with. Most digital meters use low voltage. Older analog meters use the higher voltage. A digital meter should read open and around 100k to 200k in an ohm test. Unless you have a week breaker I can not see how a pc board can cause a breaker to trip. A clamp on style amp meter should be able to find the real problem. Fist read the line current. reset breaker if needed. read one wire of the power cord at the line switch. Then move to the transformer output. AC line to the diodes.Then if meter can read DC amps, read one of the leads going to the capacitor.High power cord and no current to diodes is a shorted transformer.High power cord, high current to diodes, no current to cap is shorted or misswired diodes.High current to cap could be bad cap. make sure there is not a short at the output terminalsYou can start splitting the system up. Start by disconnecting the cap, then the diodes. see what stops the breaker from tripping. Does the push button breaker in the weld also trip?Private message sent
Reply:Originally Posted by ccawgcWhen you tested the diodes, what type of meter  did you use. And did you reverse the leads and measure both directions. A short in one direction and open in the other is a good diode.Unless you have a week breaker I can not see how a pc board can cause a breaker to trip. A clamp on style amp meter should be able to find the real problem. Fist read the line current. reset breaker if needed. read one wire of the power cord at the line switch. Then move to the transformer output. AC line to the diodes.Then if meter can read DC amps, read one of the leads going to the capacitor.High power cord and no current to diodes is a shorted transformer.High power cord, high current to diodes, no current to cap is shorted or misswired diodes.High current to cap could be bad cap. make sure there is not a short at the output terminalsYou can start splitting the system up. Start by disconnecting the cap, then the diodes. see what stops the breaker from tripping. Does the push button breaker in the weld also trip?Private message sent
Reply:PM sentHave you tried this welder anywhere else?. I would hate to think after all this that the wall circuit breaker is weak and trips easy. The same current that is tripping the breaker goes through the push button breaker in the welder. Only the fan motor bypasses the PB breaker.1 ohm in one direction and open in the other is ok. It just means you meter uses a higher voltage to test with and is turning the diode on.Last edited by ccawgc; 04-14-2011 at 01:54 AM.
Reply:here's what i read about Lincoln SP-175 the advantages/disadvantagesadvantages: MIG is the easiest type of welding to learn and is more forgiving if the operator is somewhat erratic in holding arc length or providing a steady travel speed. Procedure settings are more forgiving.disadvantages:MIG has a soft arc which will not properly weld thicker materials (10 gauge would be the maximum thickness that MIG could soundly weld with the 115 volt compact wire feed welders we are referring to or ¼" with the 230 volt input compact wire feed machine.) As the thickness of the material(steel) increases, the risk of cold lapping also increases because the heat input needed for good fusion is just not possible with these small machines. Flux-Coredhope that this gives insight about that topic. i will try to research again and add some of lincoln repair or all about lincoln here.