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

EWKehren at aol.com EWKehren at aol.com
Fri Dec 13 08:49:38 EST 2013


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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