[time-nuts] (Datum) FTS-4040A cesium, and STEL-1173 NCO chip

Javier Herrero jherrero at hvsistemas.es
Mon Apr 29 05:51:06 EDT 2013


Hello,

These people seems to have them availabe at single quantities for $65... 
perhaps not in the right packaging:

http://www.questcomp.com/questdetails.aspx?pn=STEL-1173%2FCL&pnid=372732&stock=Yes

(I've never purchased from them... si I cannot encourage or discourage :) )

Regards,

Javier

On 29.04.2013 07:51, Stewart Cobb wrote:
> Guys,
>
> I'm working on a sick FTS-4040A cesium frequency reference, which is
> basically a box and power supply wrapped around the FTS-5045 cesium beam
> module.  (Datum bought FTS, then Symmetricom bought Datum, but this 1995
> device is too old to appear on the Symmetricom website.
>
> This was one of the first "digital" cesiums.  It uses a microcontroller to
> drive a frequency synthesizer to sample many different points in the cesium
> tube's frequency response.  Part of the synthesizer is a 12.6+ MHz DDS,
> built from a Stanford Telecom STEL-1173 digital numerically controlled
> oscillator (NCO) chip and an Analog Devices fast D/A chip.
> In my unit, the STEL chip seems to be broken.  All the inputs seem to be
> correct, but the output bits to the D/A are all continuously low, so there
> is no 12.6 MHz signal and thus no lock.  The unit also throws a fault code
> "11", which translates as "12.6 MHz signal power low", confirming this
> diagnosis.
>
> Web searching gives the impression that these STEL-1173 chips are known to
> be fragile.  There was a reference on time-nuts in 2006 to repairing a
> cesium by replacing the STEL chip, In 2009, a Steve Swift who read the 2006
> thread offered to sell some STEL chips to the thread originator, but the
> deal (if there was one) was conducted off-list and I can't find valid
> contact information for Steve Swift.
>
> So it's time to consult the hive mind:
>
> 1) Are these STEL-1173 NCO chips known to fail early?  Are there ways to
> "baby" them so they don't fail early?
>
> 2) Does anyone know a source for replacement STEL-1173 chips?
>
> 3) Is there any detailed documentation (schematics, procedures, test
> points, etc) available for the FTS-5045 cesium module?  (I have the 4040A
> operators manual, but it doesn't show much detail.
>
> 4) Is there a way to tell whether the cesium beam tube itself is good,
> without the frequency synth working?  All other telemetry points (ion pump,
> electron multiplier, etc) seem to settle to nominal values after warmup, so
> I have some hope that the tube is still good.
>
> 5) Any other suggestions or hints for repairing this unit?
>
> Cheers!
> --Stu
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