[time-nuts] Schematic for the 'analog' section of an FE-5680A?

[Jamieson (Jim) Rowe]

Hi Bob,

Thanks for that tip. I have tweaked C217 a bit already, but I'll try again 
in the hope that it'll finally do the trick. By the way, which is the 
correct direction to push the frequency up a tad -- clockwise or 
anticlockwise?  I think I tried antclockwise the first time...

All the best for the festive season.
Jim Rowe


-----Original Message----- 
From: Bob Camp
Sent: Saturday, December 14, 2013 5:14 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Schematic for the 'analog' section of an FE-5680A?

Hi

One thing it could be is the VCXO not quite making it above 10MHz for long 
enough to lock. I’d tweak the cap to move it up and see what happens.

Bob

On Dec 13, 2013, at 8:49 AM, EWKehren at aol.com wrote:

> Jim
> unlike older Rb's there is very little analog in the unit. It  is sweeping
> trough its lock range so maybe you may find something around the  lamp. 
> The
> lamp should not be the problem because the 5680 has not been around  and
> been operating for extensive time before pulled.
> How ever I like to caution time nuts and be careful who they  buy from, I
> did have a bad experience with one vendor and I did post it  previously.
> False claim of new and when returned after return authorization  refused 
> refund
> since I refused to give a 5 star rating. I forwarded the emails  to ebay 
> and
> they did nothing. So any time nut that buys from ggg* fitting  deserves
> what he is getting. We have other sources out there that time nuts have 
> good
> experiences with and with the price increasing by a factor of 4 one should
> be careful. Personally I do not think they are worse the price
> Bert Kehren Miami
>
>
> In a message dated 12/12/2013 4:30:57 P.M. Eastern Standard Time,
> jimrowe at optusnet.com.au writes:
>
> 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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