Ranger 250 K1725-2 Problem

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Hello; I just joined this site. I have a tech problem with my Ranger. Its been loosing welding current. I had to keep turning up the dial for the same current setting. Now I can't even stike an arc. I opened up the machine and took some voltage readings. I get 90vdc at the rectifier output and input to the chopper. But only 19vdc at the chopper output and the welder cable lugs. I assume its suppose to be 28vdc at full current? And the voltage should vary with the current control pot? It remains at 19vdc and does not vary. This machine only has 45 hours on it. I paid $3500 new for it back in 2001. I have seldom welded with it (maybe 25 hours of welding) and was mainly used for emergency standby power on my home. The aux 240vac side works just fine. So I am thinking maybe the welding control board went dead or the chopper board is the problem? Any ideas? Does anyone know how much the parts will cost? I am very disapointed with Lincoln.
Reply:Welcome to the forum technoid  and I'm sorry to hear of your misfortune.  I know this doesn't help solve the problem but while serving as Warranty Administrator for a major fire apparatus manufacturer years ago, I read somewhere that if an electronic device is going to fail, it's likely to occur within the first 50 hours of operation - right where your unit happens to be.  You posted the model# in another thread but do you have the code#?That said, it does sound like a potential board problem although a long shot could be a dirty output control potentiometer from. . .   lack of use.  I might suggest a call to the Lincoln tech department on Tuesday to get their take on it.  They can offer whatever checks are required to narrow down the cause.I understand your frustration but assure you Lincoln has a well established reputation for building quality products and offering excellent support of same.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Thanks for the reply. The code is 10854 and serial # U1020335733. I did go to the Lincoln service site online. I sent them my info and I am waiting for a reply. My frustration against Lincoln stems from being in the middle of a welding project on my truck when it stopped dead. Left with the rod glued in place. To give you a little back ground on this machine. It was always kept indoors in a dry location. I ran it each month or so for about 1/2 hr to give it exercise. I don't think its a dirty pot. The pot is the sealed type. I have an electrical back ground in generator repair. I use to work on industrial 3 phase 480v units. The welder is simular in design but of course different after the prime mover. Current control seems to rely on the solid state welder board. I am not familiar with chopper design but from the sound it made during an arc there is a frequency mixed in the DC involved with it. Some of Tesla's ideas in action, ha ha. But anyway I'll let you know what Lincoln comes up with. I just hope its not an expensive fix.
Reply:In re-reading your original post I maintain there's a good chance it could be a board problem which would include the 300A output diode module (chopper).  I'm not familiar with these units so I dont know if the SCR drivers are on the diode module PCB1 (I suspect they are) or on the weld control board PCB3 but you could look for evidence of failed components on those.If the machine experienced a major component failure, my guess is one SCR failed which overloaded the other causing it to fail as well but it's just a guess.  Lincoln tech support should be able to assist in checking them out if things point to that.It's a long shot but did you check the security of harness plugs P50/J50 at the diode module and P12 at weld control pc board PCB3?  Pay particular attention to the pins for circuits #23 and #25 at P12.  Also check plugs P41 and P42 at the analog power pc board PCB2 and P13 at weld control pc board PCB3.  Look for the usual - corroded/tarnished/loose pins that prevent good contact.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:I want to thank you again for your troubleshoot advice. What I thought was a through the wall wire gromet was actually a plug. And it was one turn loose. These are the wires going directly to the chopper SCR. I got it to strike an arc again but the current level of the weld does not match the dial. It still does not put out the full 250 amp. More like 125. I tried burning a deep bead on a piece of 1/4 angle steel. At 250 amp It should have blown holes through it. So I think I might be firing on only half the chopper. Or something else is wrong. I put an attachment of a few views inside the welder. All the other plugs have been sealed with silicon from the factory. The chopper board is sealed with a clear hard silicon. No sign of any burning on any of the boards. So now at least I can finish up on my truck. And wait to see what Lincoln can do for me.  Attached Images
Reply:Must be talking about plug P50 and jumper J50.  I'd have to say you have a failed SCR or driver circuit for one side of the 'chopper' unit as you stated.  Determining which one (SCR or driver circuit) and which side would require the assistance of Lincoln tech of someone like member ccawgc that would be more familiar with these units.Please keep us posted.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Ok thanks. I'll try to get in touch with ccawgc
Reply:Originally Posted by technoidOk thanks. I'll try to get in touch with ccawgc
Reply:how muck lead and ground do you have on it . try to and clean the brushes on it
Reply:Originally Posted by brent thow muck lead and ground do you have on it . try to and clean the brushes on it
Reply:Well one thing's for sure - you'll really be getting to know your welder inside and out.Glad Lincoln tech is coming thru for you.  I take it they don't suspect the 'chopper'?MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:On any lincoln welder that has a shunt and has low output. the first thing I check is the shunt . put the welder on the load bank with my certified meters and check the shunt.I have found to many welders that won't putout max current that have a bad shunt.What happens is, the shunt develops micro fractures in the silver solder it is put together with and the resistance is changed. More ohms means more voltage to the control pcb.You can set the welder for 250 amps and only get 150. The control pcb is getting a single from the shunt that that says 250 amps. So all you get is 150 amps.I have had these shunts fall apart after removing them.control pcb's work best if all inputs are correct.
Reply:Makes perfect sense.  I take it the power control board compares weld output (shunt input signal) to power control pot input signal and controls the 'chopper' diode module accordingly.Last edited by duaneb55; 07-07-2010 at 01:19 AM.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Originally Posted by duaneb55Makes perfect sense.  I take it the power control board compares weld output (shunt input signal) to power control pot input signal and controls the 'chopper' diode module accordingly.
Reply:80 by eight and 90 by nine is the norm down here this time of year and the humidity runs in the lower 90% as well.  Thing is, it seems we're getting your weather while your getting ours.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Update...I got back into it this morning while it was cool for more tests. One of the tests ruled out switch and board tracking problems. Jumping out the board pins- and reading voltage across the cables- CC stick reads 77vdc, Pipe reads linear 0 -30 vdc, tig mode 11 to 12vdc. All normal. Linear tracking of the current to the mv readings from the shunt matched specs up to 160 amps. But thats with the dial at 250amp. The tech said the machine thinks there is an output short so it backs down on its current output. I have the Lincoln techs scratching their heads on this one. With the welding cables shorted using a rod as a fuse, the shunt input to the welder board is pulled, the welder does go to full output ( clamp reads 300amps very brief but then the engine surges trying to cut back). To fast to get a stable MV reading on my Fluke from the shunt. So now since I do not have a load bank I was told to connect a long run of #2 cable coiled up for some resistance. They want to know the mv's when it hits 300 amps again. The tech thinks it might be just a bad shunt. Or there may be more than one issue going on here. They don't want to rule the board being bad till all other possible checks are done. These guys are good. A new board costs $800!  It got to hot outside so I will continue this again early in the morning.
Reply:check your math on the shunt. a 400 amp shunt read 50 mv when 400 amps are going through it. 160 amps should give you 20 mv. if you are getting 50 mv at 160 amps the shunt is bad. the welder will phase back only if the shunt voltage is to high. yes duaneb55 you are correct. about the shunts function.in cc mode the shunt is used to control the output. in cv mode it is only used to protect the welder from over current problems.keep digging
Reply:Originally Posted by ccawgccheck your math on the shunt. a 400 amp shunt read 50 mv when 400 amps are going through it. 160 amps should give you 20 mv. if you are getting 50 mv at 160 amps the shunt is bad. the welder will phase back only if the shunt voltage is to high. yes duaneb55 you are correct. about the shunts function.in cc mode the shunt is used to control the output. in cv mode it is only used to protect the welder from over current problems.keep digging
Reply:Final test complete. With 50' of #4 for a load and the shunt wires pulled, the machine opened up to 270 amps and 33mv's. The shunt is good. Its come down to a bad weld control board. $877.00 new. So I called a local  Lincoln repair shop. He is looking around for a used board. The other option is I can try to fool the weld board by placing a pot in series with one of the shunt wires for more current output.
Reply:Originally Posted by technoidFinal test complete. With 50' of #4 for a load and the shunt wires pulled, the machine opened up to 270 amps and 33mv's. The shunt is good. Its come down to a bad weld control board. $877.00 new. So I called a local  Lincoln repair shop. He is looking around for a used board. The other option is I can try to fool the weld board by placing a pot in series with one of the shunt wires for more current output.
Reply:Originally Posted by technoidupdate...I put a 1k pot in series with one of the shunt wires. As soon as 1 ohm was tuned in the machine would just jump up to 270amps. So there was no way to fool it into a normal linear current output. Then later on during welding at 125 amps the machine just quit welding. Its on its way to a Lincoln dealer this week for repair.
Reply:OUCH!  Sorry to hear it wound up being the main board.It IS a 9yo unit but perhaps if you plead your case with Lincoln based on the low hours, maybe just maybe they'll cut you a break on the cost of the replacement.  You can ask the shop to go to bat for you  but I'd go directly to Lincoln Customer Service and give it a try.  One never knows.Oh yeah - don't forget to ask for the old board back too.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Originally Posted by duaneb55OUCH!  Sorry to hear it wound up being the main board.It IS a 9yo unit but perhaps if you plead your case with Lincoln based on the low hours, maybe just maybe they'll cut you a break on the cost of the replacement.  You can ask the shop to go to bat for you  but I'd go directly to Lincoln Customer Service and give it a try.  One never knows.Oh yeah - don't forget to ask for the old board back too.
Reply:Originally Posted by technoidThanks for the advise. I called Lincoln. Because of the age of the machine he said there is a slim chance. But if this was a common problem with this early model they might consider it. They will be getting back to me. Thanks again for giving me the idea to call.