Mike, the most likely use of that mysterious pot is for final frequency adjustment. You might just not have measured with sufficient resolution.
I agree with you that the oven temperature theory makes not overly much sense. If you want to know for sure, you may check what the pot is connected to. Adrian [email protected] schrieb: > Bob, > > I still have a problem with the various theories. Again, how is it measured? > If you have a production line, you don't want a "tweak" that requires hours or > days to determine. > > As far as setting the crystal set point (presumably the inner over set point), > that makes even less sense. Consider that they clearly knew the turn over > point of the crystal BEFORE it was packaged. They wrote it on the sticker > inside. > So, they would have no need to adjust the inner oven. That could easily have > been done on the bench during assembly. It could also be done via a selection > from a standardized set of components. That temperature is "sort of" critical. > The curve is very flat, to it could be a little off. Since they knew the > crystal turn over point in advance, there wouldn't be any need to "hunt" for > it by an elaborate procedure after assembly. > > However, the temperature of the outer oven is much less critical and I would > suspect is simply set by the choice of components. And, if it needed tweaking > then it could also have been done on the bench. Since they would know the > thermal transfer characteristics, I suppose that they could measure the outer > case's temperature to deduce the correct temperature of the outer oven. But, > again, that doesn't make sense from a production standpoint. It would simply > take too long. > > Perhaps, they would be willing to eat the time needed for that type of > adjustment, but it doesn't seem likely. All they would need to do would be to > add some monitoring circuits that they could access. I've seen that type of > thing a lot. It would be cheaper to add a few circuits for a quick adjustment > than it would be to spend the time on the adjustment. People's time is worth a > lot more than a few components. > > On the other hand, tweaking the output voltage is something that is quickly > measured as part of testing. Put it in a jig, make a quick check for > functionality, tweak the output voltage and you are done. Or, perhaps it > adjusts the duty cycle, the bias point or some other characteristic of the > output signal. Perhaps it adjusts the reference voltage. I think I showed that > it doesn't make a large change in the frequency. But, it doesn't make sense > for it to make a small change (although I would be unable to measure a small > change). > > I think that there are a lot of unexplored possibilities, but I definitely am > not convinced that it sets either the inner or outer oven temperature. There > are simply better ways to do that in production. > > I really, really want to know, though! I am going to try to repair mine one > more time and see what I can measure. I didn't try very hard the first time, > but I think its worth doing. If I can get it repaired again (I have to fix > some traces, especially for the ground pin) it will probably take a couple of > days. I have the parts to fix my fan circuit in my oscilloscope and I will do > that first. And possibly tweak the power supply capacitors to reduce noise. > > > Mike > >> If this is a double oven, there are two oven circuits and two oven >> controllers. >> Both would have a set point and both would be adjusted somehow. The pot >> may be the adjustment on the outer oven. Get things all set up and packaged, >> then adjust the outer oven to make things do what the should do. > _______________________________________________ > 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.
