Micro-Ion gauge

It's better to keep the MSD under vacuum if possible.  The ion gauge isn't necessary for operation, but it provides useful information to determine if the system is operating properly.

It's better to keep the MSD under vacuum if possible.  The ion gauge isn't necessary for operation, but it provides useful information to determine if the system is operating properly.

Thanks very much for your answer. I applied the vacuum for this short-term storage.
I was curious about the Micro-ion E gauge in our operation. In the manual, it is optional in EI mode but required in CI mode. I believe we operate it in EI mode all the time, so then can I simply operate it without the IG attached? We checked the resistance of the Gauge pins yesterday and found it's broken. It is a very expensive to buy new, so I ordered a cheap one from ebay to give a shot. Still, it would be great if I can use MSD without it.

If the O ring, cap, and clamp are good NW16 vacuum parts and the system pumps down normally - - -yes, you can operate it without the optional high vacuum ion gauge.

Thank you very much! I'll make sure to have those items correctly. Our instrument (5975C MSD) has been in idle condition for over an year but under vacuum up until recently I started it again. My real issue is autotune fail. The tune fail symptom is Ent lens offset that is out of range (64.26). I found in this Community that a similar case has been reported and resolved by disassembly and cleaning of HED and/or ion source. Am I right on the track? If you have any other opinion, please let me know. 

Ion source cleaning is nearly always the first step !  Yes, clean the source. You may need to replace one or both filaments, too. There are videos posted at this link that requires registration:

Eliminate the Fear of Mass Spec

You only need to clean the HED if there are noise issues, which are rare compared to a dirty ion source. A system can complete a tune with a dirty HED. It may be ugly, but it can usually finish.  

Clean the source, pump it down for some hours, then try it and report back with the results.

thank you very much for your help! I will clean the ion source and will try tune.