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Thermo Fisher Scientific

Screen current low and unstable


screen current low and unstable(GL1 SS1:1.5nA -- 2.3nA )


Titan G2 60-300


These are possible resolutions for the issue:

  • Replace SCA


These are possible causes for the issue:

  • SCA defective


  1. Screen current is low and unstable
    • GL1 SS1 large screen 1.5nA to 2.3nA
    • GL1 SS1 small screen 150nA to 220nA
    • GL3 SS3 large screen 0.23nA to 0.28nA
  2. Customer doesn’t know when this issue occurred, they normally use GL3 SS1
  3. Tip looks fine, no ring collapse, FEG emission 280uA--->normal
  4. SCA battery is 22.5V--->normal
  5. The connection and the wire itself was verified--->normal
  6. The screen vacuum feedthrough was also verified--->normal
  7. Replaced SCA and issue fixed.


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