Re: crushed walnut shells and Tek 500 series scopes


 

Hi Steve,
All of your contributions to TekScopes are, by definition, not off topic. If anything, I regret that you don't have the time to contribute more often.

All that I know about observing the private lives of electrons as they do so many unexpected things is a direct result of the oscilloscopes you and your fellow Tek engineers developed. I have been the beneficiary of many contributions you made to the instruments, patents, and trade secrets Tek developed.

I spent so many years working on aerospace products, recording studio products, and MEMS products assembled in clean room conditions that I forget they all need to be spotless. But it never crossed my mind how Tek cleaned their instruments. Until now I always assumed they never needed to be cleaned. I realize how stupid that sounds since all traces of grease. Flux, and later in my career, infinitesimal particles had to be completely removed.

I tested each of the MEMS chips I worked on in one company thoroughly for any sign that something got inside them with a PIND (Particle Impact Noise Detection) test. (https://www.youtube.com/watch?v=OL4zGxDrQXE, the fun starts at 1min, 40Sec into the video). From the perspective of an integrated circuit this is a brutal test but since our MEMS accelerometers were used by the army to test ballistic shells this was required.

Air propelled crushed walnut shells are used to clean many other things like automobile intake manifolds and valves, jet and turbine aircraft engines, bronze sculptures, and even boat hulls.
Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of ditter2 via groups.io
Sent: Friday, January 15, 2021 11:28 PM
To: TekScopes@groups.io
Subject: [TekScopes] crushed walnut shells and Tek 500 series scopes

Dennis – I hope you don’t consider this off topic. It is not on repairing a classic Tek scope – but an aspect on how they were made.

After reading the posting from the Peter Keller on the Coketron, it reminded me of another unique Tek process few know of, which I would like more details on The process is “sandblasting scopes with crushed with crushed walnut shells”.

Those who have seen the insides of any 500 series era Tek scope know the beauty of the ceramic strip construction hidden under the covers. The passive components and wiring harness are interconnected on a series of ceramic strips, with notches each containing a shiny fillet of silver bearing tin-lead solder. Have you ever wondered how Tek removed the solder rosin from the ceramic strips after assembly? There is no rosin showing on the ceramic strips, unless the scope has been repaired after it left the factory.

The solder rosin was removed from the ceramic strips with an air propelled abrasive cleaning method using – crushed walnut shells. It is similar to sand blasting, but with higher volume, lower pressure and lower velocity air. I was never able to see this in action while I worked at Tek, but many of the older engineers I worked with attested to the use of this process. (When I joined in 1978, Tek was still finishing up producing the last remaining type 1A1 plug-ins for a large long term contract with the US Army. I toured the production area, but did not see the cleaning operation at the time.) I know that the Tek Materials catalog had a Tek part number listed for crushed walnut shells used for this purpose. I was told that some delicate components, such as the beam lead Tek made TDs, special rubber covers were placed over the component prior to cleaning to prevent the lead being cut by the blast.

As I have never seen the operation, perhaps another member who has can answer these questions:
What was the size of the blast gun / nozzle?
How were the crushed shells removed from the scope after cleaning – vacuum cleaning?

Steve







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Dennis Tillman W7pF
TekScopes Moderator

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