Hi Stu; Interesting, I have a problem Datum 4040A as well. I purchased it several years ago and when it fail to work correctly I put it aside. I wonder if mine has the same problem, I find your assessment that the STEL-1173 is problematic interesting. I have found over the years that certain models of equipment have a weak link and that most of those models that fail will have a common poorly designed or selected part. Thomas Knox
> Date: Sun, 28 Apr 2013 22:51:37 -0700 > From: [email protected] > To: [email protected] > Subject: [time-nuts] (Datum) FTS-4040A cesium, and STEL-1173 NCO chip > > 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 > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
