Before you completely abandon ship, you might want to open it up. I have opened two Ovenaire OCXO's (an OSC 85-50 from an HP 5316B and an OSC 49-38C from an EIP 545A) and made repairs. The first was low amplitude and I just made a change in a resistor value in the output stage of the oscillator to increase the gain of that particular stage.
The last was off frequency and would not come on frequency with the external 20 turn pot. I opened it up, adjusted the cap and it still would not come on frequency. I then separated it into its three parts (oscillator, output board, and oven assembly), cleaned off the dust then 'reverse engineered' the oscillator and output boards to generate a schematic of each. Once I thought I understood how the circuit worked, I reassembled the unit, turned it on to allow it to stabilize, readjusted the cap (with the 20 turn pot set to mid-range) and it 'magically' worked. It's been stable for a couple of weeks not. Not sure what I did to fix it but it seems 'fixed'. They are relatively easy to open by just digging out the epoxy and sliding out the contents, removing a couple of screws on the sides first. Might be fun to explore. Joe -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Frederick Bray Sent: Friday, May 10, 2013 1:47 AM To: [email protected] Subject: [time-nuts] OXCO Issues Thanks to all who responded. I have learned a lot. It looks like the oven is still cycling and changing by about 10 Hz. I thought I had it licked when it was stable for several hours last night, but by this morning it was up to its old tricks. I am going to go ahead and pass along the unit to a friend. Thanks to all the help I got here, I am going to recommend that he replace the OXCO with something more modern. It looks like a $25 Morion from ebay will do the trick and the Cushman will probably do what he needs it for with this upgrade. Since they are cheap, I might even shotgun most of the remaining electrolytic capacitors in the main supply before I give it to him, as well as replace the resistors that are well beyond tolerance. The one nice thing about the Cushman 5110 is that it uses enough common discrete components to be quite repairable and most of them seem to still be available. Thanks again to all who helped. Fred Bray KE6CD _______________________________________________ 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.
