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  Garmin GPS showed wrong date

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Author Topic:   Garmin GPS showed wrong date
6992WHALER posted 09-23-2010 12:37 PM ET (US)   Profile for 6992WHALER   Send Email to 6992WHALER  
Sitting on the dock at Birch Island a couple weeks ago, Buckda and I noticed that my Garmin 3206 GPS and his Garmin 2010 showed the wrong date. While my old Garmin 48gps was correct.

I went to Garmin's web site and found a software update.

I installed the update last night, the date is now correct on my 3206.

The 3206 is networked to a second 3206, a sonar, radar and XM weather. I downloaded the software to a data card and placed it in one of the 3206 units. It was interesting to watch the screens as the system scrolled through all the components and updated something on all of them. It took about 5 minutes to complete.

jimh posted 09-23-2010 08:27 PM ET (US)     Profile for jimh  Send Email to jimh     
This is a good example of the beauty of modern electronic instruments--problems with them can be cured with software updates. Thanks for the information.
jimp posted 09-24-2010 11:10 AM ET (US)     Profile for jimp  Send Email to jimp     
Sort of related.

I have two Garmin 75s (one from buckda - thanks and it works great) and both show the wrong date (Dec something 1990). Garmin no longer supports the Garmin 75 (they're from the early 1990s anyway).

Both units track great and agree with my RayMarine A70D so I'm assuming the date is a software update problem and is of no real consequence? (That's a question).

Another maybe related point is that both have internal memory batteries (CR2032 3V button batteries, a common size). Both memory batteries had run down and both had lost all memory and wouldn't retain new "memory" aka waypoints. I replaced both batteries. You're supposed to send to the factory, but since Garmin didn't support them anymore I opened the units and replaced them (removed the old and soldered the new in).

So back to the question. Wrong date is no problem?

JimP

Chuck Tribolet posted 09-24-2010 04:14 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Id suggest getting the latest firmware for those Garmin 75's.
GPS dates wrap every few years, Garmin has probably fixed that.


Chuck

jimp posted 09-24-2010 04:46 PM ET (US)     Profile for jimp  Send Email to jimp     
Chuck -

Sadly, Garmin wasn't too helpful:
"...I'm sorry to read that the date is still showing incorrectly. Unfortunately, there is no setting that can be changed to fix this date. When the unit acquires a satellite signal, it should receive the date and time from the GPS satellites. The GPS 75 appears to no longer interpret this information correctly, and there is no adjustment that can be done for this." And no offer of further assistance.

JimP

Marlin posted 09-25-2010 08:46 AM ET (US)     Profile for Marlin  Send Email to Marlin     
Garmin's reply was not particularly accurate. It's true that the satellites downlink time/date information. However, date is in the form of a week index, from 0 to 1023. The GPS receiver is responsible for converting that to a normal calendar date. See http://www.colorado.edu/geography/gcraft/notes/gps/gpseow.htm for a somewhat technical discussion on the topic.

-Bob

jimh posted 09-25-2010 09:21 AM ET (US)     Profile for jimh  Send Email to jimh     
Bob--Thank you for the pointer to that excellent technical reference on the problem of GPS Week Number Rollover. That was likely the cause of the error in the two GARMIN GPS receivers. The GPS Week Number is provided by a parameter of 0 to 1023 weeks from the start of the epoch. If a GPS receiver was on the wrong epoch, an offset of 1024 weeks would about 19 years 8 months.

The observed error was noticed in August 2010 and incorrectly indicated the date was December 1990.

December 1990 + 19 years = December 2009

December 2009 + 8 months = August 2010.

It seems very likely that these GARMIN GPS receivers were being affected by the GPS Week Number Rollover problem, but now a new software patch from the manufacturer has made them compliant.

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