Hi Paul,
Thanks for those helpful comments. You have certainly pointed me in the
right
directions, I suspect.
Best wishes for the Festive Season.
Jim Rowe
-----Original Message-----
From: paul swed
Sent: Friday, December 13, 2013 10:10 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Schematic for the 'analog' section of an FE-5680A?
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
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