GC/MS 5975c is not pumping down

Hi all,

We have a 5975 MSD that is failing to pump down. The turbo pump (Pfeiffer HiPace 300) does not appear to be spinning up, though the turbo pump electronic drive unit has power and is displaying LED light activity. The rough pump has been serviced recently and should be drawing a proper vacuum. All MS cooling fans appear to be functioning properly. The screen on the MS indicates that the pump down has been initiated after powering on the system. ChemStation is giving no error message that would explain why the system is failing to pump down.

Any suggestions?


  • With the power off, disconnect the two cables to the front part of the analyzer and leave them disconnected. Open the analyzer door and try pumping down while looking down into the turbo pump, I use a flashlight to help see the blades.  When the rough pump sucks air through them, the blades typically turn somewhat or even spin quite a lot. Then when the turbo power turns on, it's very obvious.  

    If the blades don't spin or they just wiggle back and forth, the pump itself must be replaced.  These pumps spin at about 60,000 rpms all the time....and have a limited lifespan.

    DO NOT unplug or plug those cables in to the analyzer side board with the power on as the side board will be permanently damaged if you do.

  • Thanks, we don't see any spinning in the turbo pump. Could the LED light pattern be a clue for the main problem? I am afraid the turbo pump might not be the main cause of the problem, and we might realize later that something else caused the malfunction of the turbo pump. Do you have any knowledge about the normal LED light pattern in a functional turbopump?

  • The turbo pump failure rate is much, much higher than the electronics.

    If it doesn't spin at all that way - the only other thing to try safely is to take a thin tool, like an autosampler syringe needle, and see if you can gently push the blades to move them. These blades should spin very easily. If they don't move, it's dead. What you are describing is a very typical failure mode of a turbo pump.  It spins ~60,000 rpm it's whole life. It's working fine, gets shut down during system maintenance, and won't restart.

  • I guess I misunderstood your suggestion first and responded based on our vision after removing the cover. Today, we checked the turbo pump itself and we found it is working fine after the start of the pumping down, but shut off after few seconds presumably due to lack of vacuum. So good thing is turbo pump is not dead, but it is still a mystery why it doesn't come up in normal condition. Notice that our GC/MS is in CI mode and we had an intermittent problem with our gas controller for a while. Could that be a clue for the turbo pump malfunction?

    I appreciate your time

  • The turbo tries to drive higher for much longer than a few seconds. The timeout to get above 80% is seven minute (5975 T&M manual page 174).  Since it starts, the drive electronics are at least mostly working. Now look at the display - What is the rough vacuum reading?  Does it show any turbo speed during the attempt?  The speed readback from the pump back to the system is required. If it doesn't know it's spinning, it stops assuming it's probably not.   If the readback is not reading back, it's still probably a failed pump.

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