Hi Mark,
I am not sure about the design of your OCXO but recently I repaired an
Ovenaire from a Cushman 5510 service monitor.
I found that there was a bad trimmer pot in the oven control circuit.
This wasn't apparent until I started monitoring the current drawn by the
unit while trying to adjust the trimmer pot. I found that if I barely
touched the adjustment screw, the current would vary greatly. The
temperature swing of the crystal made it impossible to adjust the
oscillator trimmer cap properly. These problems disappeared after I
replaced the trimmer pot.
To get the new pot to a reasonably close starting, I measured the
setting of the old one after I removed it and duplicated that on the new
one before installing it. I had to make an extra hole in the outer case
to access the pot adjustment. Although there was a hole in the internal
foam to access the pot, there was no corresponding one in the outer
can. I adjusted the pot for the minimal variation in oven current while
monitoring the output frequency for minimal frequency swing.
Now, based on observations conducted over a few days, the OCXO barely
wanders and I would guess is within what Cushman required at the time
the 5510 was built.
Good luck with yours.
Fred
On 6/12/2013 7:48 AM, Mark C. Stephens wrote:
Anybody have service, schematics or experience for one of these OCXO?
They are commonly seen in early HP 8566A spectrum analysers.
It is out of adjustable range.
Fortunately I had a spare OSC 49-61C floating about and replaced this off
frequency reference with it.
However the replacement tends to wander about a fair bit.
By removing the 4 bottom screws and the 2 top screws, applying a little heat
with a heat gun around the bottom to melt the glue, the oven came apart with
little protest.
I was able to carefully access the top 2 boards and there is no sign of
component failure there so it maybe something inside the oven itself.
I have stopped here until I get further information.
-marki
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
