Troubleshoot my old SP-100

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I have an old SP-100 that has never failed me since I bought it in September of 1990. I went to use it the other day and found an issue. I set everything up and pulled the trigger to find the wire would slightly burn and spark (very similar to when you don't have the ground clamp set properly for a good connection). I checked the voltage control and turned it to max with my wire speed around 5. I then tried to get a spark off the ground clamp to make sure I had things hooked up alright. Same thing happened with only small sparks and no burning of wire. I checked all the connections of the ground and positive cables. I pulled the gun connection to the machine and steel wooled the brass and put lubricant on the o-rings. I changed the wire to make sure it wasn't bad. Then I pulled the cover off to test the voltage through the switch and it went through it's change up to 28 volts and maxed out. I then checked the volts of the capacitor and it went up when the unit turned on and drained off when it was shut down. The only thing I couldn't check was the amps between the hot and ground posts. My meter only went to 10 amps max with the machine going to 90, I didn't want to blow my meter. Any thoughts or other things to check? Any help is appreciated!
Reply:Check the power cord?DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:I get plenty of power, the fan kicks on and the wire feeds just fine. I just don't get enough connection to burn the wire. It sparks a little bit but that's it.
Reply:maybe a worn contact tip , these are very sensitive or a worn liner .make sure you have the correct size tip &liner , they cannot be sloppy  and still work.[SIZE="5"Yardbird"
Reply:sounds like a very common problem. check the diodes.
Reply:The SP100 was my first welder in early 1994.  Too bad I had to sell all my nifty tools to pay divorce expenses less than 6 months later. I have recently acquired a MIG140... anyways....  Did you do a complete visual inspection of and check the continuity of the work cable?  The symptoms seem like there is a high resistance in the work cable - like a frayed internal break somewhere along it's length.  Has it been kinked or damaged somewhere?  Try using another cable.  A high-quality heavy-duty automobile battery jumper cable (black side only or red side only) might work in a pinch if that is all you have.Member, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.