Need triac for Lincoln SP135.

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My fleamarket Lincoln SP135+ won't turn the argon on and off - it welds fine, but the argon starts flowing when the master on-off switch goes on, and keeps running until the machine is switched off. For now I have been turning the tank on and off manually, which actually works pretty well but wastes some gas.I pulled the PCB and found Triac 1 showing obvious signs of distress - burnt and bubbly. Since everything else looks good I figure it might be worth trying to replace before I send it toff for repair.Only thing is, the triac is so bubbled I can't read any numbers on it.Anyone know how what the correct triac would be, or whether there are any all purpose ones that might do the job?I know enough electronics to replace the triac, but not enough to know what I should be replacing it with.
Reply:Looks like:TRIAC-T220, 6A, 400V, 2500Dhttp://www.onsemi.com/pub_link/Collateral/T2500-D.PDFMM200 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:Wow, thanks!How did you ever figure it out so fast? Originally Posted by duaneb55Looks like:TRIAC-T220, 6A, 400V, 2500Dhttp://www.onsemi.com/pub_link/Collateral/T2500-D.PDF
Reply:Trade secret. 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:If the triac is destroyed and it's controlling the solenoid you have to check the solenoid as well. It might have a short.Triac shouldn't break just by themselves. They work kind of like an AC relay, but cheaper and silent. However if they are switching a higher current than designed for they can get overheated.
Reply:Yeah, I am a bit nervous about that as I know very little about electronics other than how to solder. But the triac is obviously toasted, and nothing else is, so for a couple bucks it seemed reasonable to try replacing it.Odd thing is the welder welds just fine only you have to turn the gas on manually, and the wire stays live all the time. Originally Posted by Pete.S.Triac shouldn't break just by themselves. They work kind of like an AC relay, but cheaper and silent. However if they are switching a higher current than designed for they can get overheated.
Reply:Originally Posted by kylemorley1Odd thing is the welder welds just fine only you have to turn the gas on manually, and the wire stays live all the time.
Reply:Yes, its alive even when the trigger is not pressed. Why if it won't weld with the (bad) triac removed would it mean the contactor is working? Not sure I follow your logic.Though there doesn't seem to be a contractor, in the sense of a electro-machanical device - just some bigger triac-like devices on the circuit board, on large heat sinks. Originally Posted by Pete.S.Do you mean that it's live even without pressing the trigger?In that case the contactor is also permanently on - if it has a contactor...could be a triac as well I guess.One way to test if something else is broken is to remove the triac you know is broken and then turn it on. If you you can't weld when you press the trigger it's logical to assume that the contactor/whatever that breaks up the circuit is working.
Reply:Originally Posted by kylemorleyYes, its alive even when the trigger is not pressed. Why if it won't weld with the (bad) triac removed would it mean the contactor is working? Not sure I follow your logic.Though there doesn't seem to be a contractor, in the sense of a electro-machanical device - just some bigger triac-like devices on the circuit board, on large heat sinks.
Reply:Put the new triac in, and fired up the machine  - the wire remained dead until I squeezed the trigger, and the solenoid turned on and off as it is supposed to.  I welded with it for about 20 minutes and everything seemed fine. Time will tell if it really was the triac, or if the toasted triac was just a symptom of something else, but it's looking good.Thanks to everyone who helped me with this!