[time-nuts] "Chinese" MV89A OCXO oven oscillation

[Bill Hawkins]

Not familiar with the oven, but that's a classic case of a PID
controller with too much gain. If analog control parts are used,
look for defective parts that determine amplifier gain. If it's
done with a microprocessor, look for a physical cause like too
much voltage to the oven or shorted turns that reduce the oven
resistance.

It could also be a faulty mounting of the temperature sensor
that introduces too much time delay in the loop.

Bill Hawkins
 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Yuri Ostry
Sent: Saturday, June 08, 2013 10:30 AM
To: time-nuts at febo.com
Subject: [time-nuts] "Chinese" MV89A OCXO oven oscillation

Hello,

Does anyone have any experience in fixing MV89A's that have oven
oscillation after warm-up (current consumption fluctuate with a
0.8-0.9 sec period from almost zero to approx 0.7A)?

While cold, OCXO drawing about 0.96A and there is no fluctuations.
During warm-up current drops, and somewhere around 0.55A it started to
oscillate. Amplitude of oscillation is rising slowly, and in a minute or
two reaches maximum.

Purchased three OCXO from ggg*fitting few months ago. As always, good
working condition was promised.

Two of three had really good external appearance, third was dropped, one
of corners was bent.

Just got time to test - all three were defective (broken output bypass
cap). One in addition have lots of spurs in output spectrum, and another
have oscillating oven.



--
Sincerely,
 Yuri                          mailto:yuri at ostry.ru


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