Problem with tuning on GC MS 5975D. Tune portion passed, but MassGain, MassOffs, EMGain are not normal

Tune evaluation, report are attached. Thank you in advance!

  • This is an Air.U tune...  What if you run atune.u ?

    MassGain and MassOffset are the parameters used to set the mass assignment.  Those numbers are not necessarily unusual compared to other 5975 tunes I have but may be different than tunes from your instrument.

    How old is the electron multiplier? It's at 2000V, which is still in the acceptable range, but if it is older than a couple of years with typical use it may be time to be replaced. This system was built in 2008 so should have had at least three or four EMs replaced over time.

    The unusual number in this tune report is the foreline pressure. It should be more typically down around 50 or so.  This is a diffusion pump system. How long since the last full preventive maintenance was done on the pumps - both replacing the diffusion pump fluid and the rough pump oil?  Diffusion pump fluid loss over time can cause strange pumping speed/capacity issues and worse.  If you feel comfortable doing it, remove the cover, clean the diffusion pump fan, and take a look at the fluid level.  If it is running and hot, make sure that the dancing fluid level is well within the full hot range.   If the level is below that, it is critical that the system gets vented and the fluid replaced - or at least topped up to be in the proper range.  The diffusion pump heater is a fixed wattage heater and if there is insufficient fluid the temperature can get too hot, crack the fluid, and ruin the pump or worse....

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