[time-nuts] Symmetricom Power On Counter

Skip Withrow skip.withrow at gmail.com
Mon Jul 25 15:55:57 EDT 2016

Hello Time-Nuts,

I just ran a Symmetricom X72 for 10 days to check the rate of the Pwr HRS
counter.  At one point I thought I did this with an SA.22c and found a
discrepancy between actual number of hours run and the counter increment.
I can report that the X72 does appear to count hours correctly.  After
running for 233 hours the hex counter incremented by 233 decimal.

This leaves me with some questions though.  The counter in the unit is four
hex digits giving a max count of 2^16 or about 65,000.  The life of the X72
is supposed to be about 20 years (roughly 180,000 hours).  So what happens
to the unit on overflow, does the counter just rollover?  So how do you
tell a new unit from one with 70,000 hours on it?  And there is also a
service bit that is supposed to switch when there are several months of
life left, what drives this bit?  Is it some kind of lamp life measurement
(like the LPRO), and is the power on counter involved in any way?

The Symmetricom X72 and SA.22c seem to be cousins, I have not played with
an X99 and don't know if it is related.  If someone has insight into these
units I would be most interested in knowing some of the answers.  In fact,
the 'w' command dumps about 26 different values (all in hex) and having the
secret decoder ring for what the item mnemonics are and the scaling of the
displayed values  would be very useful.  The user manual lists the 'w'
command but gives no information regarding the resulting display that I can

Thanks in advance for any help.

Skip Withrow

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