[time-nuts] FE-5680A sweep range setting

Paul Berger phb.hfx at gmail.com
Tue Feb 18 14:37:45 EST 2014


I have a couple that look like the one in these pictures minus the the 
little frequency control board. 
One of mine would not lock so what I did I looked at my other 5680A 
which is the type referred to in the tip about C217 and looked at how it 
is connected in relation to the crystal  for the VCXO, which is very 
close to C217.  In the ones that I have with the stacked cards this 
crystal is on the middle card with a little block of foam over it.  Near 
this crystal is a trim cap C245 that seems to be connected the same way 
relative to the crystal and by adjusting it I was able to get mine to 
lock, but did find the adjustment to be a bit twitchy and since it is on 
the middle card, you need to remove the top one every time you want to 
tweak it a bit.

The one that I have are marked with option 57 and instead of having a 
flange around the edge like many of the telecom surplus ones it is 
mounted on a piece of 1/4" aluminum plate.    The top card has a PIC on 
it and there is a RS232 level converter chip there but it looks like the 
connection only go to the 5 pin connector next to the SP232ACT RS232 
chip.  This one does not require external +5V and in fact bring out the 
10MHz on pin 4 where others seem to connect +5V. there does not appear 
to be any PPS output either.  These also have a cutout to expose the 15 
pin connector that is on the base board in front of the physics package.


On 2/17/14 11:03 PM, Simon Lyons wrote:
> Hello everyone,
> I have a 5680 which is failing to lock. My DDS frequency is 8388608Hz, 
> but it's sweeping between about 8388638 and 8388740. My unit has 3 
> levels of PCBs in the DDS/VCO corner and there is no trimcap labeled 
> C217. Does anyone know how to adjust the sweep center frequency on 
> this type of 'triple decker' unit?
> Thanks,
> =Simon=
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