[3dem] Column vacuum problem with a Tecnai F20

[R.I.Koning at lumc.nl]

Dear John,

I just had a short discussion with our FEI service engineer here in the
Netherlands. Indeed, as pointed out earlier by others, it most probably
is a leaking O-ring in the vicinity of the cold trap or possibly even in
the compustage. So the big question is which one it is. 

In order to prevent a long series of tests and replacements that do not
solve the problem he advises to do a helium leak test. Here at Eindhoven
there is such an apparatus. You might want to ask your service engineer
to do such a test. (Basically you add another pump to the vacuum system
with a Helium detector inside. You add helium from outside your
microscope and detect the helium going through the pump). It is not a
simple thing to do, but probably better than testing every O-ring
individually.

Best regards,

Roman

R.I.Koning (Roman) Ph.D 
Leiden University Medical Center
Department of Molecular Cell Biology
Section Electron Microscopy 
Postal Zone S1-P
P.O.Box 9600, 2300 RC
Leiden, The Netherlands 
( (+31) 71 526 9296
1 (+31) 71 526 8270
* r.i.koning at lumc.nl 
" http://www.lumc.nl/1050/research/electron_microscopy.htm 

-----Original Message-----
From: 3dem-bounces at ncmir.ucsd.edu [mailto:3dem-bounces at ncmir.ucsd.edu]
On Behalf Of John Rubinstein, U of T
Sent: Tuesday, July 22, 2008 6:53 PM
To: 3dem at ncmir.ucsd.edu
Subject: [3dem] Column vacuum problem with a Tecnai F20

Dear Colleagues,

We have been having a strange vacuum problem with our FEI Tecnai F20 G2
.  Our engineer says that he has not come across reports of this problem
through FEI, but I was wondering whether anyone in the 3DEM community
has seen the problem before and knows what the cause is.

Our column vacuum deteriorates when liquid nitrogen is added to the cold
trap.  At room temperature the column vacuum (IGP1) sits at around 13.  
Upon addition of liquid nitrogen, IGP1 deteriorates to ~20.  We have
aready had some work done on the microscope and learned some interesting
things.  We had the component that couples the external copper braid to
the cryobox replaced but that did not solve the problem.  Subsequently,
as a test, our engineer  removed the cryobox from the column and blanked
off the cryobox bellows.  Without these components,  IGP1 improved to
~5-6.  However, replacing the cryobox bellows with a new one did not
solve the problem. 

As you will know, vacuum leaks can take a long time to sort out, so any
advice that helps us solve this one faster would be greatly appreciated.
Also, could people who use a F20 (with or without film) please send me
some typical values for their column IGPs (IGP1 and IGP4 in our
instrument).

Best wishes and many thanks,
John

--
John Rubinstein
Molecular Structure and Function Program The Hospital for Sick Children
555 University Avenue, Rm. 3330
Toronto, ON
Canada
M5G 1X8
Tel: (+001) 416-813-7255
Fax: (+001) 416-813-5022
www.sickkids.ca/rubinstein


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