[time-nuts] HP 10544A Repair

[Richard (Rick) Karlquist]

If you replaced the thermistor with an exact replacement,
then you shouldn't need to change the pot.  If you didn't
replace the thermistor with an exact replacement, then you
should carefully measure the resistance of the pot as you
found it.  (I hope you did not fool with it already.)  From
the pot resistance, and the thermistor curve specs of
the original thermistor, you should be able to calculate
the factory oven temperature set point.  You can then
calculate the new pot resistance based on the specs
for the replacement thermistor.

Trying to determine the turn over temperature as you
described (which was done with an automated system
in the E1938A) would be extremely cumbersome when
done by hand.  It would be a last resort if you fooled
with the pot.

Rick

On 2/27/2016 6:48 PM, Nigel Vander Houwen wrote:
> Hello All,
>
> Relatively new to the group, but thought I’d ask for a bit of advice. I have an old HP 10544A ovenized oscillator that was pull from some equipment some time ago because it got too far off frequency to phase lock with the external reference. It looks like the thermistor in the oven controller failed, and just wouldn’t ever turn the oven on.
>
> I’ve replaced the thermistor, and the oven is working properly again, but I need to tune the temperature as appropriate for this crystal. I’ve read that this involves plotting crystal frequency vs temperature, so I’ll need to adjust the potentiometer inside, close it up again, wait for temperature to stabilize, and take a frequency measurement, and iterate.
>
> If I’ve understood what I’ve read correctly, I’m looking for a flat in the frequency response of the crystal with regards to temperature.
>
> I do have a HP 5345A referenced from a thunderbolt to do the frequency measurement.
>
> Am I on the right track? Further insights? Etc?
>
> Thanks all!
> Nigel
> K7NVH
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