Achim Vollhardt wrote::
Fellow time-nuts,
my humble HP10811 + Shera controller combo signaled loss of lock since
about a week after 5 years of non-stop operation. Frequency
measurement showed it to be ca. 90 Hz low and the added oscillator
enclosure (8mm aluminum case) barely exceeded room temperature.
Measurement showed oven current to be zero and after some Google
research, the thermal fuse for the oven controller became the prime
suspect.
Opening the oscillator is rather easy due to screws, pulling the inner
isolation lid as well. With help of the service manual, the fuse is
quickly identified and proved indeed to be open.
I had a 24V, 1.5A polyfuse at hand which was soldered in parallel to
the existing fuse. 1.5A seems a bit large, however I think some
derating is advantageous due to the elevated temperatures. Closed
everything and first connected the oven supply only:
<snip>
Regards,
Achim
Achim,
You're not the first with this problem. Search the archives for tons of
conflicting advice:
http://www.google.com/search?btnG=1&pws=0&q=site%3Awww.febo.com+%22thermal+fuse%22
--
Sylvain RICHARD
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