[time-nuts] FE 5680a 3pay 36.89 includes shipping. Finally ordered one

Robert Benward rbenward at verizon.net
Wed Jan 4 04:15:30 UTC 2012


Hi John,
I did you what you suggested and it locks now.  I tweaked so that the output 
is only 10-20Hz above 10MHz.  It seems to lock on the way down from the peak 
(high) frequency, it doesn't seem to lock on the way up.  It seems to agree 
with one of your plots, but no the other.  You don't say what he difference 
is between the plots.  It is sensitive to vibration, it seem to unlock 
easily when bumped.  Do you know what the other trimmer is for?

Bob


----- Original Message ----- 
From: "John Beale" <beale at bealecorner.com>
To: <time-nuts at febo.com>
Sent: Tuesday, January 03, 2012 1:29 PM
Subject: Re: [time-nuts] FE 5680a 3pay 36.89 includes shipping. Finally 
ordered one


> On 1/3/2012 8:20 AM, Robert Benward wrote:
>> I got mine for around $25 in a regular bidding affair. Mine had trouble
>> locking, It only locked a handful of times, and that took forever, but 
>> most
>> of the time it just sat there and cooked. The seller replaced it and the
>> new locks up in 2 or 3 minutes. I did not have to ship the old one back.
>> The Lock output signal doesn't seem to have enough drive to turn on an 
>> LED.
>
> One of the three FE-5680A units I got behaved exactly that way. Turns out 
> some part of a VCXO circuit had drifted over time (I assume) so the 
> free-running frequency never quite reached up to 10.000 MHz enabling lock 
> to the signal from the physics package. Assuming you do have a 10 MHz 
> output signal, put a counter on it while it is warming up and look at the 
> frequency. After I fixed it, the frequency vs time from startup plot 
> looked like this:
> https://picasaweb.google.com/lh/photo/7E22rkh_YivyesrnTog6atMTjNZETYmyPJy0liipFm0?feat=directlink
>
> The fix was to take off case top and bottom and tweak the trimmer cap 
> marked C217 slightly, it is near Y200 (crystal with round PTC thermistor 
> attached). Here's a photo of that part of the board: 
> https://picasaweb.google.com/109928236040342205185/FE5680A?authkey=djqVhWs9LkM#5680683008490223330
>
> Of course there may be some completely different problem with your unit, 
> but it's something to try, if you want to open it up and play with it.
>
> -John Beale
>
>
> 




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