Below is a copy of the message I sent and received from Stan Griffiths,
W7NI. For those not familiar with Stan, he worked for Tektronix for 30
years from 1960 through 1990 in Field Sales, Service in and out, etc.
He is also the author of "Oscilloscopes: Selecting and Restoring a
Classic."
73, Garey - K4OAH
Glen Allen, VA
Hi Garey,
I have a LOT of experience with this issue. The failure of most Tek
transformers is internal contamination of the CRT filament winding. Most
Tek power transformers have a 6.3 VAC CRT filament winding that is elevated
to the CRT cathode voltage. This is -1350 volts in the 530 and 540 series
and can be as high as -4000 volts in a 519. I think the 560 series is about
-3300 volts, if memory serves me correctly. The leakage caused by a
contaminated CRT filament winding kills the high voltage supply.
It is almost always ion-contaminated water that ruins a Tek transformer.
Here where I live in the Portland, OR area, the water is relatively ion-free
and there was generally no problems with contaminating transformers of
washed instruments that were done at Factory Service here.
I ran into severe failure problems washing Tek scopes in San Diego. We lost
several when we finally had the water tested. Bingo! The solution was to
get a water deionizing system installed and monitor the water purity for
ions. I think we got it from Culligan and it is quite like a soft water
system but specifically for ions. The water is chemically treated as it
flow through tanks. The chemicals are eventually depleted and the tanks are
replaced with new ones delivered by the Culligan Man.
Tek did have an interesting transformer warranty. From the 1955 Tek
Catalog:
"Tektronix transformers manufactured in our own plant carry an indefinite
warranty."
It did not specifically say "lifetime warranty" but it was administered that
way. All of the transformers that got ruined by the San Diego water were
replaced free of charge by Tek. This was in the mid to late 60's. Some
years later, Tek changed their transformer warranty and it became one year
like the rest of the parts in the scope. I don't know of anyone who has
tested to see if Tek would still honor the "indefinite warranty" if you
presented them with a failed old transformer today. I doubt you would get a
free one!
So the transformer "fatality index" is directly dependent on the quality of
the water used in the wash process. It was probably 50% in San Diego with
untreated water and 0% with treated water. It is probably less than 1% here
in the Portland, OR area with untreated water.
You may share any of this data with the other list.
Stan
-----Original Message-----
From: Garey Barrell [mailto:k4...@mindspring.com]
Sent: Monday, November 02, 2009 3:11 PM
To:w...@easystreet.net
Subject: Washing TEK Scopes.
Stan -
There has been a discussion going on on another list regarding TEK
"washing" scopes. I was working for NASA back in the 60's, and I was
told by more than one sales rep that power transformers were often
casualties of this process, but that since TEK had a lifetime guarantee
on power transformers it didn't really affect the customer.
There have been quite a few posts contradicting this, and I'd be
interested in your recollection/info regarding this process and the
"fatality" index.!
Thanks!
73, Garey - K4OAH
St Charles, IL
Drake 2-B, 4B& C-Line,& TR-4/C Service Supplement CDs
<www.k4oah.com>
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