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Hi Probe folks;
A few weeks ago I posted about having a pretty crummy image on my 733. It took us a while to find it, but I figured I'd report back for the record.
Two different problems: One was that our aperture holder was pretty dirtied up inside. That was the cause of the low-frequency undulation in the image. After that was cleaned up and a new aperture strip put in we were left with the strange high-frequency image shuddering.
I thought for a bit that was something with the stability of the scan generator, so I went through the electronics for that for about a week to no good resolution. Then I decided to check the objective lens itself. Turns out the signal controlling the objective lens was not stable (sawtooth waveform), and so in effect there was this 10 kHz "wobble" in the lens focus. After another week of electronics hunting I tracked it down to a specific electrolytic capacitor that appears to have failed on one of the Electron Optics System's box's boards. I replaced that friday and the 733 has had a stable image ever since.
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Electron Microprobe Lab, University of Minnesota
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