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

[EWKehren at aol.com]

I warned time nuts a year ago about ggg*fitting. They always claim new and  
what you get is garbage. I bought a "New" 5680 and when I found out that it 
was  very old and defective they agreed to refund my return shipping cost 
but  when I refused to give a 5 star review they refused the refund after I 
shipped  it. ebay did nothing. I had the emails. So any one that buys from 
them gets what  he deserves.
Bert Kehren
 

 
 
In a message dated 6/8/2013 4:57:12 P.M. Eastern Daylight Time,  
bill at iaxs.net writes:

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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