[3dem] Problems with Gatan US4000 blankers

[Pasi Laurinmäki]

Dear EM community,

I wonder if some of you have experience with problems regarding the  
beam blanking by Gatan Firstlight control unit.

Our system: FEI Tecnai F20 & Gatan Ultrascan 4000 & Gatan Digital Micrograph
We have recently had the power supply in the Firstlight break down and  
then replaced. After the replacement, operation was ok since we could  
do all the calibrations as well as normal imaging.

However, now we have a problem. In short, the beam doesn't blank when  
it should (Situation: flood beam)
-if I look at dark reference it has high counts
-flood beam image, if dark corrected, has near-zero counts (because  
dark ref is "hot")

When images are taken blanker led's in the front panel of Firstlight  
flash on and off as normal. If (as Gatan specialist suggested) I  
disconnect override-cable from back of firstlight I should be able to  
see (with viewing screen down) the beam blanking on and off as the  
image is recorded. This doesn't happen, the beam stays on constantly.

I have tried different shutter idle settings under DM camera config.  
My shutter idle settings are now both shutters closed. I have checked  
the shutter cables (running from back of Firstlight shutter 1 and  
shutter 2 to microscope cabinet X10 and X11) and they look fine. Under  
camera acquire advanced settings i have tried both pre- and  
post-specimen shutter. To my understanding, because Firstlight  
frontpanel leds show operation, the fault is somewhere between  
Firstlight intelligence and the actual physical blankers in the  
microscope cabinet.
Is it possible that the problem is in the microscope hardware? How to  
check for that?

Looking forward for your suggestions,
-Pasi Laurinmäki

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Pasi Laurinmäki  Laboratory Engineer

Institute of Biotechnology
Electron Microscopy Unit
P.O.Box 56
FIN-00014 University of Helsinki
Finland

tel. +358 9 191 59502
fax. +358 9 191 59498
E-mail. pasi.laurinmaki at helsinki.fi
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