I have been using a HOTSPOT capacitive discharge welder to mainly weld the tips of type K thermocouples. We needed to expand the use of capacitive discharge welding because we have a project that requires me to weld thirty 26-gauge type K thermocouple wires to a 3/8-inch thick steel plate for heat dissipation testing. We purchased a new HOTSPOT II welder to do the job because it has a greater range of operating power. I had no problem, well as much you run into trying to capacitive weld thirty 26-gauge thermocouples to a 3/8-inch steel plate. Since that time I have heated the steel plate and thermocouples up to about 600°F several times. Two of the thermocouples I am using have broken free and I cannot get the welder to reattach them to the surface of the steel plate. Though I can get either of the HOTSPOT welders to weld new thermocouple wires, I cannot get them to weld the ones that broke free from the steel plate back onto the steel plate. I also can't get the 26-gauge thermocouples to weld the two wires together. I have cleaned the steel plate and thermocouple wires mechanically using a file and wire brush. I can get a new thermocouple wire to weld but not the ones that have been heated. I can also get either welder to weld other small metal objects. Has the heating of the steel plate and thermocouples changed there structure somehow that will not allow the discharge welder to operate properly? I do not want to either get new 26 gauge type K thermocouple wire or a new steel plate to try to get the setup testing again. Can anyone give me any idea what might be happening between the thermocouple wires and that steel plate that has caused the capacitive discharge welder to not operate as intended?