[time-nuts] Z3815A date problem fixed?

Morris Odell vilgotch at bigpond.net.au
Fri Jan 24 10:59:06 UTC 2014


Hi all,

There was some consternation here 5 months ago when Z3815A GPSDOs began
reporting a date 1024 weeks in the past. This was due to a storage overflow
condition in the Furuno GPS receiver in the Z3915A. The designers probably
never anticipated that they would still be in use 20 years later....
Oscillator discipline was unaffected as the 1 pps was still good.

Obsessional types like me looked for a solution. There didn't seem to be any
knowledge out there about reprogramming the receivers so it had to be a
transplant.

Furuno GT-8031 timing receivers are available on ebay and not prohibitively
expensive. They are about half the size of a matchbox and work at 3.3V TTL
levels. The interface connector is a 2mm pitch 2X5 pin header and the
antenna connection is a pigtail with a Hirose u.fl connector. The interface
is 9600,n,8,1.  I picked one up a few months ago and it took a while to get
the appropriate connectors etc but I eventually found enough time to make a
little interface PCB compete with a Li button cell backup battery. I lashed
it up tonight into the Z3815A and it works!!! 

The GPS locks the oscillator and the Z3815A reports the correct time & date.
As I write this it's been going for an hour or so and the survey is not
complete, the Z3815A still reporting reduced accuracy. It is showing an
antenna alarm for some reason so the yellow "operation" alarm LED is lit.
That may be because I'm powering the receiver externally at the moment and
there would be no current being drawn from the Z3815A 5 volt supply. I'll
work on that in the morning. The interface board draws a total of about 100
mA including the antenna current and I'm hoping that won't be high enough to
give an antenna alarm in the other direction. If so I'll have to change the
3.3 volt supply from being zener stabilized to being series voltage dropped.

More news as it breaks!!

Morris




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