[time-nuts] Datum 9390 Problems

David I. Emery die at dieconsulting.com
Mon Mar 23 20:57:23 UTC 2009

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

	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 at 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."

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