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

Stewart Cobb stewart.cobb at gmail.com
Tue Apr 30 03:24:14 EDT 2013


>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 ...

You could try powering it up and checking its telemetry with the Monitor3
program available on the Symmetricom website.  If it's like mine, after
it's fully warmed up, the "DAC gain" and "numeric gain" will be maxed out,
and there will be a bunch of alarm codes. One of them will be alarm 11. The
Monitor3 program (which was designed for a newer model of cesium) will not
translate that code, but the 4040A manual says it means "12.6 MHz signal
power low".  If you get that error, it's worth probing the lines between
the STEL chip and the DAC. Mine were all stuck low.

The STEL chip, its DAC, and related filters and amplifiers are all just
under the top cover of the unit, on the far right of the PCB as seen from
the front.

Units with serial numbers lower than 2000 apparently used a different
frequency synth scheme that does not include an STEL chip.

Cheers!
--Stu


More information about the time-nuts mailing list