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HacDC is in the process of refurbishing a scanning electron microscope: a Cambridge Stereoscan 200.

SEM in workshop

Current Status

Roughing pump works, turbo spins up to full speed for a while but then slows down. The vacuum controls operate but don't light up as expected, and the pressure readout is not showing a reading. The console turns on and produces video output with the correct data overlay. The filament control reads "bad filament," despite the filament continuity being OK. There is an interlock between the pressure gauge and console that may be keeping the filament off. We'll need to verify the pressure gauge output and see how to trigger that interlock.

We received and installed an MKS Micropiriani 925 vacuum gauge that measures vacuum up to atmosphere. After pumping down, we bottom out at .34 torr. There is a gross leak in the tube on the side of the machine. we are now reverse engineering the electronics. we have replaced the seals on the up-tube, and are working on controlling the column with a microcontroller, rather than the giant desk-sized console.

See Stereoscan_Operators_Log for details.


  • A suspected leak between the main imaging chamber and the top of the electron gun cylinder is preventing the chamber from reaching pressures low enough to sustain a proper beam. The plumbing connecting the two consists of two elbow brackets. The top and bottom of the long elbow bracket use 2-1/4" diameter black rubber (Viton?) gaskets/O-rings. The bottom elbow bracket uses a 2-3/4" gasket to couple to the chamber proper, and has an adapter between 2-3/8" and the 2-1/4" at the bottom of the long elbow bracket. These are compression-style fittings; the rubber is compressed between two metal pieces and completes the seal.

[Image of Vacuum Bracket](

Manuals and Images

Pfeiffer Balzers TPU TPH 170 manual
Similar but smaller unit manual File:Pfeiffer Balzers TPH TPU 110 .pdf
Table of pumps to compatible controllers File:Pfeiffer table.pdf
View of pump 1 Media:PfeifferTHP190_1.gif
View of pump 2 (connector side) Media:PfeifferTHP190_2.gif
View of pump 3 (other side) Media:PfeifferTHP190_3.gif


757 Labs

Previous owners (757 Labs, another hackerspace) attempting repairs compiled some information at:

Additional Resources

  • The original S200 operating instructions are available at the space in a three-ring binder near the machine.
  • If possible, members will also have access to a PDF copy of Scanning Electron Microscopy - A Student's Handbook, 1980, self-published by Michael Postek, et al. This book was widely used by microscopists and is still regarded as a good learning reference, but the original binding is rare and prone to falling apart. It might be possible to use the PDF copy for private, educational use.

More Photos


We have a list here of HacDC members who are responsible for the SEM, including people that should be notified about problems.

Mirage335 (talk) Custom electronic control replacement circuitry.

Juri_ Julia Longtin, Juri_ on IRC. SEM repair project.

Pages in category "Stereoscan"

The following 3 pages are in this category, out of 3 total.