Agilent 5975 MS Tune --- lawn of peaks / peaks not found !

[Javier del Campo]

Dear Colleagues,

Please enlighten me with your knowledge...When doing manual tune (air leaks check or PFTBA check) in my 5975, I am finding either a lawn of peaks (all masses shown) when EM volts is set to 2000 or so...or no peaks at all when using the EM value of my last successful autotune (1129). The main clue comes from the fact that neither filament glows when doing scan tune.

This problem began after the instrument was put operation again after a programmed stop. Venting procedures etc were properly followed. Now the vacuum is 2x10-5, PTFBA bottle is one quarter full (actually pressure rises when doing tune scan)...After venting again I dissasembled the source, all electrical wiring and electronic boards are ok...I changed one filament...problem persists...How can it be that the filament is not glowing? Unless there is electron emission there will no chance to have ionization...Thanks for your help!

[tkubowicz]

Hello

As you can't see filaments on please check:

-wires from filaments to small side board (check if pins and plugs are not loose)
-check cables that are plugged to analyser door (from boards to analyser)
-check in tune settings both filaments (switch them and save file)

Regards

Tomasz Kubowicz

[Javier del Campo]

Thank you Tomasz for your answer. I followed the first two points and everything was ok. Regarding the third point, exchanging the two filaments or the tune settings does not make any difference...no peaks found. Could it be some electronics related to the filaments assembly? Thanks

[tkubowicz]

Hello

Check if voltage for filaments is -70eV in manual tune. You can always load tune file from last week/month and try to tune it again.
If you have 2 new filaments and you can't see them glow it could be electronic board problem.

Regards

Tomasz Kubowicz

[James_Ball]

The lawn of peaks or just "grass" as we call it in our lab, comes from raising the EM volts above the point where it is giving a noise signal above the threshold value across the entire scan range. There is actually no ions present, it is just electronic noise.

Do you receive any errors when attempting to scan? Usually if filaments don't come on you get the "no emission current" error. If you are not getting this error it could possibly be a problem with the filament driver circuit. On the small board mentioned above you should be able to locate the filament pins in the circular pattern of pins there and check them with a volt meter, you should get 70v DC on those if the current is reaching that point. If not then the current is not being passed from the main board where the filament driver is.

[Javier del Campo]

When scanning, there are no error messages at all...checking the filaments pins, I am getting 70V DC...reached this point, I think diagnosis in situ by Agilent technical representatives is the next step...Thanks all for your contributions

[James_Ball]

When scanning, there are no error messages at all...checking the filaments pins, I am getting 70V DC...reached this point, I think diagnosis in situ by Agilent technical representatives is the next step...Thanks all for your contributions

If you have a volt/ohm meter, pull the source and check continuity between the filament pin and the source. There should not be any conductivity between either pin and the source body. If there is conductivity then the voltage going to the filament is instead going to ground on the source and that would prevent the filament from glowing but also not give the error of a broken filament. It they are grounded, then it could be that one of the filaments is bent and coming into contact with the source body.