GC/MS 5977A Source Cleaning, 502 down after cleaning

We have 5 GC/MSD's.  I have been performing their Maintenance for over a decade.  On 4 out of the 5, no problems.  On MS #5 though, every time I perform a source cleaning (same as all the other source cleanings I do) the 502 drops, sometimes over 3%, to <3.0% which is unacceptable for our requirements.

In the past I've re-cleaned the source many times (following the proper cleaning protocol through Agilent as well as their maintenance technicians), replaced parts (sometimes a random part might make it seem like it's worked but then dropped shortly thereafter), exchanged the whole source for a new one, switched filaments, switched polarity, and run blanks and samples, all in an effort to get the 502 back to where it was before the cleaning.  It seems to just want to take time, and time being several weeks for it to creep back over 3.0%.

Any advise or suggestions would be appreciated.



I've now re-cleaned and replaced: both repeller insulators, the lens insulator, and the drawout plate.  Switched polarities and filaments. Baked out.

And 502 is still <3.0% in atune.

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