A blog on the repair, operation and calibration of surface analysis systems and components including electron spectrometers, sputter ion guns and vacuum related hardware. Click on the Index tab below to see a list of all posts. Visit our website at http://www.rbdinstruments.com
Glassblowing has been around for thousands of years, and we see examples of it every day. From neon signs to Murano glass to Chihuly glass exhibits. Less well known but very important to science is the art and craft of scientific glassblowing which is the process of creating glass apparatus used in research and production.
Over the years I have had the good luck to be working at universities on one or another type of vacuum chamber related instrument where some glass to metal seal was damaged but was able to be repaired by the resident glass blower. More recently it seems that many of the glassblowers at universities are retiring and not being replaced. So, to an extent, scientific glass blowing is becoming a nearly lost art as this interesting article on the History of Glassblowing explains.
But all is not lost as there are still scientific glass blowers who are handing down their glassblowing expertise to those who will carry on the tradition.
Some of the older PHI electronic units have a type of heat sink with a built-in spring tab (shown in the picture below) that forces the back of a transistor into the heat sink. Over time, the spring tab can lose tension (most likely due to heat induced metal fatigue) and then the transistor no longer connects to the heat sink, eventually resulting in the transistor failing due to overheating.
For units such as the 32-100 Electron Multiplier Supply, overheated transistors are often the cause of multiplier voltage output problems.
For this blog post we will look at a 32-100 electron multiplier supply with no output on the CMA high voltage output. The problem was isolated to a bad TIP120 transistor which shorted out and melted because the back of the transistor separated from the heat sink over time.
In addition to replacing the TIP120 transistor, we also modified the heat sink to ensure a good contact with the transistor.
To modify the heat sink, you need to first remove the defective transistor and then remove the heat sink. You will need a hot soldering iron as the heat sink has enough mass that it will drain away some of the heat from the soldering iron. You can use a solder sucker or some solder braid to remove the solder from the heat sink contacts.
Once the heat sink as been removed, break off the spring tab.
Next, drill a small hole in the back of the heat sink where the indent is located. We used a 9/64″ drill bit since we needed to clear a 6-32 screw and lock nut.
Put some heat sink compound or conductive tape on the back of the replacement transistor. This is necessary to ensure good thermal transfer from the transistor to the heat sink.
Use a screw and lock nut to attach the transistor to the heat sink. Make sure that the transistor is centered in the heat sink. In this case we also added another small heat sink to the back of the original heat sink to add some additional cooling for the transistor.
Next, insert the transistor leads into the holes on the board and insert the heat sink into the larger holes in the board. Solder the heat sink and the transistor leads. Cut the excess leads from the transistor and remove any excess flux from the board.
Now that we have replaced the transistor and improved the transistor to heat sink contact, the 32-100 should perform well for many years.
Since we were replacing the one defective TIP120 transistor, we also replaced the one for the SED supply as well (and modified its heat sink) as a preventive measure. In this case we could not add the extra small heat sink due to a tight clearance to the nearby transformer. Even so, the improved contact to the heat sink will provide improved heat transfer from the transistor and result in improved reliability.
Need help with your older PHI (Physical Electronics) surface analysis system electronics (or optics)? Contact us at rbdinstruments.com
As of January 1st, 2022, RBD Instruments has discontinued support for our PCMAPII interface boards used on legacy PHI / Perkin-Elmer scanning auger electron spectrometer systems such as the model 590 and 600.
This blog post lists all of the documentation related to the PCMAPII interface board. If your PCMAPII board develops a problem and this documentation does not help, please contact RBD Instruments for other options.
The links below will open up PDF files that you can view and print.