[time-nuts] Datum 9390 Problems

Magnus Danielson magnus at rubidium.dyndns.org
Mon Mar 23 22:23:35 UTC 2009


David I. Emery skrev:
> 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.

What magical GPS week number did we just hit?

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:

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

> 	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.

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

> 	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.


>> 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...

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...


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