Difficulty with hed power supply

Hello everyone,
I have a MSD 5975 that exhibits the error "Difficulty with the HED supply" only when attempting auto-tune. I realigned the wires around the quad and did not help. The HED itself does not seem to be dirty. Is there a way to find if the HED power supply is working correctly without disassembling the whole unit? It uses a turbo pump and the pump oil level is OK, so, according to the troubleshooting guide, it must be something on the detector or the electronics. Any help would be appreciated. 


  • HED – A High Energy conversion Dynode. The word Dynode was first used in 1922. It is a “plate that emits impact electrons”. In Agilent GCMS systems, it does not have a magic coating.  It is just a metal plate with -10,000V on it when the instrument is collecting data.  The HED power supply makes that voltage, is supplied by other internal power supplies, and controlled by other electronics. The HED supply itself is pretty simple.

    In Manual Tune, filament on, PFTBA on, Repeat Profile Scan or Spectrum scan, do you get the same error?   In Manual tune, there's a place to turn off the HED.   If you set it to OFF and then filament on, PFTBA on, Repeat Profile Scan or Spectrum Scan - does it work or do you get other errors/faults?    If it works with the HED set to OFF and doesn't with the HED set to ON - there is not much an operator can do.

    Vent, power off. 

    Verify that the HED cables - the white cable with orange ends on it near the back of the analyzer - is connected on both ends, to the HED feedthrough on the side plate and to the HED suppl,y and the other cable, this one is the yellow unipolar supply for EI only systems, is connected properly, too.

    HED Cables

    Inside the analyzer the connector is a solid metal wire pressed into the HED high voltage feedthrough on the inside of this same side plate connection as seen above. With a gloved hand, pull the wire out of the connector and reinstall it.  Verify that the electron multiplier wire is not touching anything and is installed properly at the same time.

    Then pump it down and try it.

    If that does not work, the best thing to do is to contact Agilent Service.

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