I had the same problem with my MTS250S. What happened with mine is the wire conduit in the gun was arcing and I had to put in a new liner. Then it did it again in just a few minutes of use. I opened up my door to the wire and saw that the power terminal had gotten hot because it was blackened . I took the cover off the machine and the wire inside that connected to that terminal was loose and alowed the terminal to get hot and arc. So I had to put in a second gun liner and cleaned the turminal and tightened it up good. I called Ray at Everlast repairs and he wanted pictures of the damaged terminal so while I had it out to clean it up I took pictures and emailed them to Ray. He said that he had to get the parts from china because it is not something they have needed to keep in stock. He said it would take about a month, that was 6 weeks ago and I have not heard anything from him. I put mine back together with the old parts that had been cleaned and it has been working all right. I asked Ray if that would cancil my warranty and he said no. I hope this helps.