Hi,
I have a couple that look like the one in these pictures minus the the
little frequency control board.
http://www.flickr.com/photos/14336723@N08/sets/72157632394339366/
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.
Paul.
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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