I was having a problem tuning the mass spectrometer. The tune would start out normally then the main peak for the higher masses would disappear and only be noise. Noticed that the EM voltage was approaching 3,000 so I replaced the EM horn. It works much better and the EM voltage is lower but if I do the full autotune the same problems occur 3 out of 4 times. If I just do a quick tune it works every time. All the instrument users are happy and it looks like they are getting good results (univerisity setting lots of students using the instrument). I would like to fix the problem since I assume the problem will get worse over time.