Hi Fred, Also, I neglected to ask, you wouldn't have the OXCO pin outs would you?
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Frederick Bray Sent: Thursday, 13 June 2013 2:01 AM To: [email protected] Subject: Re: [time-nuts] Ovenaire OSC 49-61C 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. _______________________________________________ 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.
