Hi If the OCXO is putting out a solid signal, and it tunes up and down, the problem is not likely to be in the oscillator circuit. In this case, the heater / temperature control assembly is likely the issue. Most control failures melt the solder on the oven and then totally fail. In this case, it's *almost* keeping the right temperature. I'd bet on something in the feedback circuit on the control op-amp.
Bob On May 11, 2013, at 10:14 AM, J. L. Trantham <[email protected]> wrote: > Fred, > > I've been thinking about your OCXO issue of the oven cycling. I had a very > nice theory about what to look for and where to look. > > However, if you have an issue with the external 12 VDC supply to the OCXO > assembly, that, clearly, needs to be resolved first. Also, you could remove > the supply from the test equipment and attach a known stable bench supply > directly to the OCXO then look at current draw (cycling) and output > frequency stability. > > If your OCXO is anything like the two that I have opened, the foam is easy > to pull out. There is usually a piece of 'packing' (fiber) tape folded over > to allow you to pull the foam enclosed oscillator and oven assembly out of > the case. I would like to see some pictures if you have any. > > Can you share the model number, whether you are adjusting a cap or pot, > whether the adjustment is internal to the OCXO or external, whether it has a > 'screw' cover to the adjustment(s), and whether it has one or two ('Coarse' > and 'Fine') adjustments? > > All the problems I have had have been on the oscillator board or the output > board that is just inside the bottom cover of the OCXO. > > I am not sure about how best to 'reseal' the unit when finished. My most > recent one had not externally accessible adjustments, just an external pot > adjusting a 4 VDC source to the EFC control. When resealing it, I turned it > on, let it heat up for an hour or so, then quickly disconnected it, applied > the 'Quik-Set' epoxy, then quickly reapplied power to let it heat up again. > This gave a small bubble or two out through the epoxy demonstrating an 'air > tight' assembly. It dried with power applied. When it cools, I'm sure > there is a 'vacuum' inside. However, at operating temps, it should be at > 'atmospheric' pressure. I am about 20 feet above sea level. I don't know > if 'sea level' internal pressure at operating temperature is critically > important or not but it seemed easy enough to achieve. > > Good luck. > > Joe > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Frederick Bray > Sent: Saturday, May 11, 2013 12:22 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] OXCO Issues > > I looked inside the OCXO and didn't see anything obvious. I didn't pull the > foam out, as I didn't want to destroy everything. > > After I re-assembled everything. I hung my DVM on the 12 volt line that > feeds both the oven and the oscillator. I watched it vary by almost a > volt. I am now beginning to suspect that I should go into the main > power supply and replace at least the cheaper electrolytic capacitors. > There are a couple screw terminal units that are quite expensive so I am > hoping to avoid having to buy them. I will also check for out of tolerance > resistors. I found several on the other board of the power supply and I > suspect it is a question of heat since all the other resistors I have > checked at random elsewhere in the 5110 are fine. > > > On 5/10/2013 3:42 PM, Frederick Bray wrote: >> Thanks for the suggestion. >> >> I'll probably pull it and look inside. If it is something simple the >> problem may be fixable. >> >> Fred >> _______________________________________________ >> 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. _______________________________________________ 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.
