Repeated failure of primary fuses on Agilent MC 5975C

We are having repeated failures (3 now) were the MS just shuts down.  I can replace the fuses, but I wondering why this continues and if this is indicative of a bigger problem.  I would like some advice how to troubleshoot.  Thanks!


Jennifer Jones

  • Hi Jennifer

    We had an GC-MS issue in the past where the rough pump was starting to fail and as a result kept drawing too much current, causing some of the fuses to fail.

    We also had an issue with a rough pump (on a LC-MS) which was blowing fuses when it started. For the LC-MS rough pump we connected it directly to power rather than to the MS and start it that way. Once it was running we were then able to turn it off and connect it back to the MS and then start it - I was told that sometimes if the pump/oil is cold the current draw can be too much for some of the fuses. Not sure if you can try something similar for the GC-MS rough pump.


    Not sure if this helps at all


  • Hi Jennifer,

    Soccerdad is correct. Rough pumps as they age will start to draw more current through the AC board on the MSD. The slow blow fuses will run hotter and near their limits. The rough pump replacement should cure the fuses blowing. I would replace the pump as soon as you can as the extra demand can be a strain on the AC board. The new Pfeiffer Duo Rev G is the supported replacement G3870-80055 .



  • Thanks Soccerdad and James.


    I replaced the fuse and connected a brand new rough pump to the instrument.  I also checked the diffusion pump and changed that oil for thoroughness.  I was excited when the MS came back to life yesterday afternoon.  I allowed it to pump down over night and this morning was able to get a good Air/Water check and tune and even a 2 injections.  During the third injection, a few seconds after the detector turned on following the solvent front, the MS died.  The fuse blew again.  I saw errors 6: "Difficulty with the HED supply.  Difficulty in the mass filter electronics" and then error 204: "Difficulty in the mass filter electronics.  There is no emission current.  The high vacuum pump is not ready." 

    After the instrument cooled down, I opened up the source and everything was connected and both filaments were intact. Any other suggestions or help is most welcome. 


    Thank you!


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