TIG 250/250 trouble shooting

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I have had an older Idealarc Tig 250/250 which has worked perfectly for years in a home shop so it gets very little use. Last week, it started having intermettent problems (it woujld have power on both the Tig and stick settings and then it would go away - although mostly it was gone). The high frequency worked (when switch on). Now there is a total lack of output power.I checked the following basics: 1. 240 VAC present at machine 2. approx 75 VAC on output leads (with high freq off) 3. nothing obviously burnt within the machine 4. the main input contactor pulls in when it shouldLast night I noticed that the spark gap was arching across its points. Ssince I never noticed this before, don't know if this is normal or  not. Acording to the Lincoln manual, the gap should be set at .040". I will check and reset if required tonight. Any suggestions on where to start the diagnostics for the lack of main power at the output leads?
Reply:Well, the machine is working correct, If you'r running tig, I'd suggest that your internal conduit in your tig torch has either burned out of the harness or come loose.Try the unit in stick mode
Reply:Cruizer,Thanks fo the response. Last night the machine ran pefectly for about 5 or 6 strikes in TIG mode. Then it died again and although it had voltage at the end of the cables (approx 75 VAC in AC mode TIG) it would not strike or powe the arc. I previously tried the stick mode but will try again tonight (no difference; it had voltage at the end of the cables, but no arc power and the arc would not strike even in stick mode.)I will check the torch and cables, but doubt that is the problem since I have voltage at the end of the cables. Any other ideas?
Reply:Sounds like a possible thermostat or other safety interlock problem.  Is it possible that the Amptrol is malfunctioning?  Do you have a manual for your machine and can you post the schematic?   Can you post a link to the manual for your exact machine and code or serial number? I don't have a manual for the Idealarc TIG 250/250 in my computer, but I do for the Idealarc 300/300.  I assume they are very similar except for capacity.  The troubleshooting section suggests some things to check.  Have you done those?  My 300/300 manual does not show a schematic.  Perhaps you could start by requesting a schematic from tech support at www.lincolnelectric.com.The 300/300 manual I have is a poor quality PDF file that is difficult to read, but the parts list does show a thermostat.  Can't tell what it is mounted on.  One check you could perform is to clip a voltmeter across the thermostat leads and observe (hopefully) 0 volts when you start welding.  You should see a voltage appear across the thermostat if it is opening up during welding.  Same with other safety interlocks that may be present.  Be sure you don't leave the meter on ohms or current setting when energizing the machine.One thing to check is the current control device, whatever it may be.  What is the technology of the Idealarc?  Saturable reactor?  If so, monitor the current to the control windings of the reactor to see what is happening as you weld and as you vary the Amptrol. It would really help to see a schematic.By the way, don't assume any "expertise" on the part of anonymous posters like me in the absence of credentials.  My only background in welder technology is reading some books, maintaining my own hobby welders, and toying around with electrons for about 60 years with occasional shocking results.  If I can claim any expertise at all, it is in noise and vibration measurement and control.  I might be able to help if your welder is noisy or vibrating too much, but you would pass out at the mileage charge.awright
Reply:Did not check the forum for a while. Was doing actual welding...About your problem - schematic is VERY helpful...Can you check something: you did say that voltage exists on output. I assume that you measure it without arcing...Can you watch you meter while arcing? It seems that voltage drops to zero under load. Again, please, try to measure voltage under load....I am sure under Awright's supervision we will get there...
Reply:It seems that all TIG 250/250 produce the same PDF Attached Images
Reply:Gentlemen, Thanks for the replys. I do have a schmatic of the machine, but I need to retreve it from another computer. I will post tonight along with the machines exact model number and any additional current and voltage readings that I can take. The schematic that you posted looks correct (from memory), but I want to be sure before I get you all headed down the wrong path.The machine does use the saturatable reactor design. I looked at the voltage across the reactor control circuit and it did vary as the footpedal was actuated, but I didn't know what level of current to expect in the circuit so I didn't want to smoke my meter. Do you have any idea of the max current that should be running to the reactor control windings? (Judging by the wire size, I wouldn't expect it to be very much, but I don't have any factual numbers.)I had the same thought about the temp switches and will check those also tonight.By the way, I noted that one of you gents is in the Bay Area. On this posting screen, it doesn't show those details. FYI, I am in the SF Bay Area (Danville).Stay tuned.Chuck
Reply:NOT CURRENT! VOLTAGE!What I meant and my understanding Awright too - we want to see output voltage under load. Just clamp your meter to outputs (100V AC) and try to strike an arc while observing the meter... It is expected that voltage will drop to 0V. Establishing that - we can go and do some mesuarements inside the machine...
Reply:Scematic for my Tig300/300 is on the inside of the right hand side cover.mark61
Reply:Thanks for posting the schematic, Normand.  It helps by showing the general topology of the circuit.  However, I can't make out any text or see fine details of the wiring, even after expanding it to a full page.  Is there any way you can expand it before posting without losing resolution?And mark61, can you take a macro photo of your schematic and post it?  Or does anybody have a link to a PDF file of the schematic directly from Lincoln?Yes, Chuck, I am in North Oakland near the west end of the Caldecott Tunnel.  Maybe mileage wouldn't be so shocking if you need your machine's vibration measured.
Reply:Awright1. I've just realized what you've said - resolution is NOT acceptable of course. But there are limitations on file size and picture size (around 100KB and 800x600 max). So I guess all such schematic only can be uploaded in partial pictures.2. The link - http://content.lincolnelectric.com/p...IMS/IM315A.pdfIt is slightly different from what I uploaded. And this completely puzzles me. The picture I uploaded is IM315 which I found from office computer (And I still have it on HDD of office comp). Now at home I can not find it....?????....I mean I am finding only abovementioned IM... I will solve this mistery on Monday when I am back in office....3. But this all is not important since OP claims that he has correct schematic and machine's S/N on some other computer. He promissed to bring those here...Last edited by Nomand; 10-17-2008 at 11:13 PM.
Reply:Could be anything from a current sense circuit or output board to something as simple as a weak thermostat.. A  good tech would be able to T-shoot it in under an hour. T-shooting this one online is quite difficult.  I think I'd look at the resistors on the current sence circuit first . Looks like the holding/ current sense circuit has to maintain a certain amount of power for the weld transformer when not welding
Reply:Hey guys, for now I must eat a little crow. It appears that my power lead may be the problem. The short story is, and I am simply surmizing, at this point that the cable must have been barely hanging together (that is why I originally got a voltage reading at the TIG torch electrode) and then as I was doing some additional trouble shooting it finaly let go and all of a sudden, no voltage at the torch. When I check continuity of the power cable, it was open. Of course this occured this morning after the welding shops closed, so I can't get a replacement cable until Monday. While I was sitting around, I decided to try the stick mode again. My selection of stick rods is nonexistant, but I found an old 1/8" 7018 and the machine seems to work on AC and DC- . I say this guardily since the rod is old and I haven't stick welded for a long time. I guess that I will know Monday.A question about the power cable; I have a Weldcraft WP20 water cooled torch. It appears that power leads are available in both rubber and PVC insulation, with PVC being cheaper. My existing lead was PVC. Any recommendations on the rubber versus PVC.I took a photo of the schematic that was pasted on the inner panel of my machine and will post the schematic and teh machine serial number tomorrow or Monday (for the record).Chuck
Reply:The rubber is tougher against a hot metal burn thru. PVC will last longer but burns easier. I would suggest using one of the heat/burn resistant braided sheath over the torch cable for longevity.  35 years of welding experience speeking here. Regards
Reply:Ha, so I was right! Not bad for on line troubleshooting ehhhhh
Reply:Ok, I yield to the great Cruizer. You were correct, it was the power lead from the torch to the machine. I installed the new lead last night and the machine is back to normal.  Just for the records, my machine serial number is 590436 built in 1984.I have included the wiring diagram pasted on the inside of the machine, but the resolution that this site allows for down loading is relatively small, so the image is virtually unreadable. If anyone wants a better quality of this diagram, let me know and I can send directly in a higher resolution.Chuck Attached Images
Reply:I like on line puzzles, keeps my brain going from my overly dull life having to fix these things, as for the diagram, its available at lincolnelectric.com under owners manuals