Jim I can add some info here. What you suggest is a reasonable conclusion. On some RB modules but I do not believe on the FE-5680s there is a true lamp voltage and its very helpful in determining if the lamps old enough that as you say its dark. On those units if you are below 4 volts approx you know the reference is pretty old. I want to be careful here because someone will say "But I have one that works at 2 volts." :-) But that said there are any numbers of failures that will create the issue you could be seeing. There is a modulation signal typically in the 137 hz range and 274 Hz. There is the RF at 6.8 Ghz or so and lastly the rf that excites the RB lamp. Any of these things can be wrong and the system will not achieve lock. If its weak the lamp may glow but essentially run cool in color temperature. But at this point I can say there are indeed really great eperts on here that can give you better guidance. Regards Paul. WB8TSL
On Thu, Dec 12, 2013 at 3:05 PM, Jamieson (Jim) Rowe < jimr...@optusnet.com.au> wrote: > Hi, > > I’m an elderly time-nut newby, and I’ve already struck trouble with a used > FE-5680 Rb-vapour reference > I bought via eBay. It runs (from +16V and +5V), and the current drain > starts at 1.75A and then drops over > 5 minutes or so down to about 650mA. But it won’t lock, even if I leave it > powered up for a few hours (with a fan > to keep it from getting too hot). > > The output frequency just keeps switching up and down between about > 9999850Hz and 10000080Hz, with a bit of ‘lingering’ > near each end. And of course the ‘lock’ output at pin 3 stays stubbornly > at about 4.35V. > > To my newby brain, this sounds like the problem is either in the Rb lamp > (too dark, perhaps), or > else in the photodetector and buffer, etc, forming the ‘dip detector’ part > of the feedback loop. > > Could one of you much-more-experienced time-nutters tell me if my > diagnosis sounds right? > > Also, I’ve found a schematic for the digital sections of the FE-5680A in > your archives, kindly drawn up > by one of your very experienced members, but has anyone done a similar > schematic for the ‘analog’ > sections? I suspect I’m going to have to work out for myself where to > test for a fault in these > sections. There’s also a bit of a mystery (in my mind, at least) regarding > that little 2-pin SIL header > just near the Rb lamp, on the top of the PCB. Anyone know what that’s for? > > All the best in anticipation, folks. > > Jim Rowe > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
