[time-nuts] Symmetricom chip scale atomic clock

Lester Veenstra lester at veenstras.com
Thu Apr 24 13:15:32 EDT 2014

Affected Products: Jackson Labs or Symmetricom time/frequency reference
boards based on Symmetricom chip scale atomic clock, most common unit is the
CSAC GPSDO sold by both symmetricom vendors and direct from Jackson labs 
Type of issue: Short and Long-term reliability, mfr couldn’t assure that if
it works for 1week, 1month or 1year it is not an affected unit
Issue: CSAC Loss of vacuum, sudden onset failure mode
Result: CSAC unable to control the temperature, Indefinite warm-up state,
ultimately the unit fails to reach a lock state
Failure Rate: Vendor noted ~5% of all units, internally it has been 1 of
maybe a dozen or less units to date
Resolution Status: Issue acknowledged by manufacturer but not resolved,
still affecting all current stock and current production units, Jackson Labs
will replace the CSAC part on the board and return without a fee though
admittedly the new part may also fail
While resolving an issue with a Jackson Labs CSAC GPS Disciplined Oscillator
board, we were made aware of a reliability issue affecting all timing boards
built around the new Symmetricom Chip Scale Atomic Clocks (a.k.a. CSAC).
There is a fundamental design flaw that can result in the loss of vacuum in
the CSAC, which prevents the unit from being able to effectively control the
part’s operating temperature. The end result is a unit that is in an
indefinite warm-up state. We were informed that all current and even
currently produced units can fail in this way. The number we were given was
~5% of all units will fail, so we happened to get one of those 5%. The
failure mode is a very sudden onset failure, for our case one day it worked
and the next day (during a test of course) it did not. Also this is not a
case of ‘if it works the first week then it will be fine’, it can fail
anytime (in my case I had used it on a regular basis for several months
prior to the failure). Our unit also spent 99% of its life in an air
conditioned lab so certainly not subjected to even a remotely harsh

Lester B Veenstra  MØYCM K1YCM W8YCM
lester at veenstras.com

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