Thomas,

Thomas Folkers skrev:

I got a call from a friend that had a call from one of his customers
that had all their receiver fail in the same fashion. Their Symmetricom
receivers however reverted back to an older date. I will try to get the
details.

My conclusion is that it is a bad 1024-week wrapping routine in action.
The lack of firmware upgrade is most certainly the root cause as the
typical way to resolve it is to use a reference date near time of first
shipping as reference and then calculate away from that.

Unless you get firmware upgrades your receivers have just become a piece
of junk and you are expected to buy new...

So, you are not alone with this problem.

The lack of firmware upgrades that handles dates and signal upgrades
(such as PRN 31 and PRN 32) is a constant source of GPS failures. It
also has a very scary tendency to be coordinated. GPS receivers older
than 10 years should maybe not be kept in production unless it is known
to work and be sufficiently supported.

So, I got one of those "I told you so" moments today.

Cheers,
Magnus

Same here, it's day "597" according to my Datum 9390 Rb clock.  The time
appears correct.  Also interesting is the 10 MHz output, which appears to be
about 2E-10 high compared to a Thunderbolt and cesium standard.  That wasn't
the case when I first bought the 9390 a year or so ago, but it's been true
for at least a couple of days now.  There's no indication in the display
that the rubidium's unlocked, as the status remains "Doing GPS correction
(System check OK)".

Anyone else seeing a constant frequency error from theirs?

-- john, KE5FX

----- Original Message -----
From: "Thomas Folkers" tfolkers@email.arizona.edu
To: time-nuts@febo.com
Sent: Monday, March 23, 2009 3:10 PM
Subject: [time-nuts] Datum 9390 Problems

Symmetricom could care less, no, in fact they are rather happy as they would
like all that old equipment to be buried.

Firmware for that vintage is out of the question now. It is my understanding
that newer receiver boards solved that issue. My question, could some newer
generic receiver module be programmed/interfaced to replace that board? I
don't have a component level manual on that receiver.

I too have a couple of those units that we use simply for the disciplined
rubidium 10 meg out even though the week and year is and has been off for
some time.
Phil

On Mon, Mar 23, 2009 at 04:17:00PM -0400, phil wrote:

I have a 9390 with Rb - currently in deep retirement - that I

acquired in 2000.  It locked OK after I repaired the 16.368 MHz oscillator
lock circuit, but had the rollover date problem.

I eventually was given a small PIC microcontroller based adapter

card from a defunct 9390 someone else owned that went between the Trimble
GPS board and the Datum mother board and fiddled the serial data
messages from the GPS to correct the GPS date (as I remember it, it
added the leading 1024 bit in a 16 bit field). This corrected the date
so it read correctly.

This Datum mini board was apparently at least one of the fixes

that Datum provided customers for the GPS date rollover bug - there may
also have been some updated firmware for the motherboard, I forget.

I did disassemble the PIC code, but what I did with the results

I forget... other than decide what the board did to the data stream.

I did have a copy of the schematic and a user manual for the Datum

9390 I got from Symetricomm/Datum - this definitely did NOT include much
info on the Trimble GPS board and as I remember it the manual didn't
match the firmware I had all that well nor did the schematic match
the hardware I had exactly either.

Eventually the DC to DC converter potted module died, and unable

to locate a drop in replacement I retired the 9390 in favor of a couple
of HP 58540as and then Trimble Thunderbolts and a Datum PRR-10
disciplined Rb clock with LPRO Rbs.  The 9390 had a rather dirty high
PN 10 and 5 MHz output which  was another problem I never quite got
around to solving.

I guess it is time to look up the GPS date in weeks and see how

close to the next rollover it is...

--
Dave Emery N1PRE/AE, die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

David,

David I. Emery skrev:

What magical GPS week number did we just hit?
http://www.ngs.noaa.gov/CORS/Gpscal.html

The time of failure matches the entering of GPS week 1524. This is an
interesting number as it is exactly 1024 + 500. 500 seems like an fairly
arbitrary GPS week number to use as a base number. It matches... 1989-08-06:
http://csrc.ucsd.edu/scripts/convertDate.cgi?time=0500+0

So the magic GPS week roll-over bias is now known for these.

Strange option to make a separate board rather than modify the firmware.

Wohooo!

Can be any week now... but week 1536 (1024 + 512) seems like a likely
arbitrary week like anyone...

Maybe it is time for me to get a GPS L1 tester...

Cheers,
Magnus

On Mon, Mar 23, 2009 at 11:23:35PM +0100, Magnus Danielson wrote:

I think the intent was to supply upgraded Trimble GPS receiver

cards eventually (or firmware for the existing one, which presumably
comes from Trimble) and this fix allowed the old unmodified GPS board
and the little PIC thingy to work with the same Datum firmware that
would also handle an upgraded receiver with more bits in its GPS week
output.  Maybe some Trimble receiver boards exist that do supply the
additional bits - it is not known to me if  all 9390s which were
upgraded used this particular fix.

--
Dave Emery N1PRE/AE, die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

Register on their site and get the firmware updates from the web site,

On Mon, Mar 23, 2009 at 3:10 PM, Thomas Folkers
tfolkers@email.arizona.edu wrote: