We have a 5975C that showed a dramatic loss of sensitivity suddenly. When I check the air ions in Tune & Vacuum Control, even they are extremely low. Cleaned the source, but no change in response. I do not get any MS error messages and the filament appears okay. Ran autotune and EM jumped from ca. 1400 to 2100 and relative abundance of 219 was still really low. Unfortunately, the ion gauge burned out a while ago so I do not know what the pressure is running. I suspect the EM needs to be replaced, but I have not had one go out so quickly before (1-2 days). I also have a 5973 and I am wondering if I can insert the EM from it into the 5975 temporarily to troubleshoot the problem. The 5975C is TAD and the 5973 is not; I know the EM's are different but wondering if it will fit and work to help me conclude the EM is the problem.