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 -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.