I recently had to change the filaments on a D5975C. All proper procedures for venting and pumping down were followed. I was able to run an air and water check and atune and they both looked passed. When running my method I could tell the filament was turning off around 40 mins into the 50 min run. The filaments would not turn on after the run. I tried manual tune, etc. I inspected both filaments and they both were good. Just to rule everything out, I replaced them both again. Again allowed for the unit to pump down and stabilize overnight. Again they will turn on for the air/water check and atune, but not the method. I tried an older method and that didn't work. I replaced the tune file assuming it was corrupt and that didn't work. I checked all the connections and nothing is loose. It seems the only time the filaments turn on is when I vent and pump down, but after that they do not turn on. The vacuum pressure is hold steady at 1.35e-05. Do you have any recommendations or possible solutions to try? Thank you for your time.