[time-nuts] HP10811-60111 oven failure + repair

[paul swed]

excellent repair and pictures

On Fri, Oct 21, 2011 at 5:47 AM, Achim Vollhardt <avollhar at physik.uzh.ch>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:
> initial 510mA, going down to 105mA after 10-ish minutes. Perfect.
>
> Putting everything together again and the HP10811 is again within 0.1 Hz of
> 10 MHz without the control loop closed. Getting it back to its antenna later
> the day..
>
> For some hi-res pictures of the procedure:
>
> http://gulp.physik.uzh.ch/**HP10811_oven-repair/<http://gulp.physik.uzh.ch/HP10811_oven-repair/>
>
> Hope this is of help to anybody with the same problem.
>
> Regards,
> Achim
>
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