Chapter 4 Tecnai F20 & Tecnai F30

4.1. I don't see beam on large screen, what can be wrong?
4.2. When I put Objective Aperture in, the beam disappears, what should I do?
4.3. Neither of two Gatan CCDs are available, what's wrong.

4.1. I don't see beam on large screen, what can be wrong?

There could be a number of causes that you don't see beam on large screen. Check the followings.

  • On Tecnai F30 make sure there is a specimen rod inserted in or the beam will be blanked for safety concerning X-ray.

  • Column valves are NOT closed.

  • Vacuum status is ready.

    H.T. and Extracting Valtage is at set points

  • Beam blanker is not ON. You can check this from CCD Camera module in Tecnai interface where the Blank should not be in Yellow.

  • If SerialEM is launched and in Low-Dose mode, then you should either un-check "blank beam when large screen is down" in Low Dose control panel or simply turn off Low Dose mode.

    Note: SerialEM uses scripting beam blanker to control beam shutter, and it is independent of beam blanker from Tecnai interface.

  • Grid bar or edge is not blocking the beam. You can change magnification to lower numbers.

  • Objective aperture is not blocking the beam. You can take it out if it is at IN positions.

  • CryoBox is not blocking the beam. Check it by first going to very low magnification like 120X or so and then moving CryoBox position mechanically.

4.2. When I put Objective Aperture in, the beam disappears, what should I do?

The Objective Aperture is blocking the beam. The correct procedure to insert and center Objective Aperture is as following.

  • Make sure there is sample at current stage location.

  • Put DOWN the large screen.

    Warning: It is very important to do this before continuing to next step, as focused diffraction beam can damage CCD or other digital cameras.

  • Switch to diffraction mode, and adjust camera length to about 1 meter.

  • Put in Objective Aperture. If the edge of the aperture is not sharp, try to adjust intensity or/and defocus until it becomes clear. Now center it.

  • Switch back to image mode.

4.3. Neither of two Gatan CCDs are available, what's wrong.

Be patient! When Gatan DigitalMicrogaph starts up, it needs time to communicate with each of the camera controllers. Allow 10 seconds or so for both Gatan cameras to complete registration with DigitalMicrogaph, before starting up TIA.