[time-nuts] Schematic for the 'analog' section of an FE-5680A?
Bob Camp
lists at rtty.us
Sat Dec 14 17:57:35 EST 2013
Hi
If I remember it’s a half turn trimmer. The “right” direction will depend on where they left it …
If it’s multi turn then the answer is counterclockwise.
Best to simply watch the result on a counter.
Bob
On Dec 14, 2013, at 4:09 PM, Jamieson (Jim) Rowe <jimrowe at optusnet.com.au> wrote:
> 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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