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Author Topic:   Garmin GPSMAP Family of Devices
JBCornwell posted 03-26-2011 04:50 PM ET (US)   Profile for JBCornwell   Send Email to JBCornwell  
Ahoy, all. :) Anyone here been involved with Garmin GPSMAP Units family of marine and land chartplotters?

I have had a GARMIN 276C for about six years and use it in my car now, but have used it on my boats in the past. I have the car navigation kit with City Navigator V8, Recreational Lakes CD, and about 400 waypoints on Lake Of The Woods, Possum Kingdom, and around the country. I also have a spare 256-KB data card. I really like this unit and have become very comfortable operating it, but it has much less memory than the 376 and 378, which I think are otherwise compatible and those newer ones have much brighter screens.

Now my unit is getting forgetful. When I start up the car it doesn't know where it is or what day, date, time it is. It has to reorient itself, which usually takes a few minutes. Then it is just fine and works as well as it ever did. It takes several hours after it is turned off to forget what it was doing and have to reorient. I bought a new battery that had no effect, and did a full update of the software, also no effect.

Garmin wants a flat rate $160 to fix it. I suspect that is plus shipping and handling. There is a used 378 units on ebay for around $200. Free shipping. My impression is that the 378 is an upgraded version of the 276C with more memory, more software onboard, built in City Navigator and a brighter screen.

I am thinking that for an extra $40 I can get a good working unit with much bigger memory and a much brighter screen (a very, very big plus) and a truckload of accessories and it would all be compatible with the 276C stuff I have on my computer. Then I could sell off the leftover stuff piecemeal for a C-note or so.

Anyone agree with my thinking or see flaws in it?

RED SKY at night. . .

WT posted 03-26-2011 05:51 PM ET (US)     Profile for WT  Send Email to WT     
I have the GPSMAP 478 and had problems in acquiring the satellites (I suppose it forgot where it was.). When I called Garmin there was a way to reset the unit. I think on start up you hold down your "out" button along with the "power" button.

You might call Garmin to ask about a reboot or reset.

Good luck,


Jefecinco posted 03-26-2011 06:28 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Buying used electronics is risky. If the used unit works well what have you gained? Another old GPS with limited functionality that may last for a week, a year, or a decade.

The technology is moving so fast that a new unit would probably serve your needs better and for a longer period.

OTOH, it may meet your requirements and be in good condition.


JBCornwell posted 03-26-2011 09:49 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Yup. I recognize the risks of buying used stuff, Butch. The problems are that a new unit with the capabilities I want (and have) would cost me a Grand or more and obsolete about a Grand worth of extras I have bought over the years. I am not destitute, but an unplanned Grand would hurt. Might even not read my waypoints from my 'puter. For my use I have no need (or want) for the weather, radio, etc. that the newer units offer.

I spent a couple of hours on the landline with Garmin Tech Support (Really helpful and motivated people) while they downloaded the latest updates and tried other software tricks to make her remember. . . to no avail. :( Then I bought a new battery with the same result. Shoulda known better. I preach almost daily about not trying to troubleshoot by replacing parts. Thanks, anyway Warren.

I am currently thinking to bid on the 378.

RED SKY at night. . .

jimh posted 03-27-2011 07:48 AM ET (US)     Profile for jimh  Send Email to jimh     
A GPS receiver needs to keep track of the current time and its current position, even when turned off. An on-board battery usually keeps those functions alive. It sounds like the on-board battery may have degraded.

If the unit is very old, the on-board ephemeris of satellite orbit data may be too out of date to predict current orbits. This will cause a long delay in satellite acquisition.

JBCornwell posted 03-30-2011 11:17 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Thanks, Jim.

Actually, that was my first thought when this fault appeared, but the Tech Support guy at Garmin said that the unit should get date and time from the first satellite that the unit reads when turned back on, then select the "sky" it should read at the location where last turned off. That seemed logical and would allow long term storage.

But . . . how does the unit know what satellite to interrogate if it doesn't know the correct date and time and therefore what satellites are visible?? This is very frustrating for a guy who used to teach programming in binary and hex. 15 years ago I was a leading edge technocrat in instrumentation. Now I wonder if I know anything at all.

I replaced the removable battery. No joy.

I updated the operating system. Still no joy.

The 378 got bid out of my range long before auction close.

When I turn the unit on I now just go straight to reorientation. Yesterday it came on declaring the date to be 12-21-99.

Should I just bite the bullet and send it to Garmin for "reconditioning"??

goldstem posted 03-30-2011 11:35 AM ET (US)     Profile for goldstem  Send Email to goldstem     
any interest in a 176c I have laying around? haven't used it
in two years. it's time to go! not as nice as the 276 for sure. but the price would be right! also have a bunch of accessories for it.
jimh posted 03-30-2011 11:38 AM ET (US)     Profile for jimh  Send Email to jimh     
I am not an expert of GPS receivers, but I believe that happens when a GPS receiver is first activated is along these lines:

--the receiver wants to know the date and time

--the receiver wants to know is approximate position

--based on the date, time, and position the receiver predicts what satellites may be in view to it

--the receiver tries to find a signal from a satellite using a particular psuedo-random noise coding.

The signals from GPS satellites are all sent on the same frequency and are modulated with different psuedo-random noise (PRN) encodings. This is called a spread spectrum technique or carrier division multiple access (CDMA). The signal to noise ratio of satellite signals received here on earth are not very great, and the PRN encoding actually helps them be received with better immunity to interference.

The receiver makes an educated guess about what PRN to use to listen for a signal. If the PRN is not the correct PRN for one of the satellites that is actually in view, the receiver will not find any signal. After a while it will give up and try another PRN. It repeats this process until it finds the first satellite.

Since there are 32 PRN sequences, it can take a while for the receiver to stumble onto a satellite if there is a serious error in the data, time, or position.

To predict what satellites will be in view, the receiver needs to have an ephemeris of the orbits. If the ephemeris is out of date or cannot accurately predict the current satellite position, the acquisition of the first satellite signal may take a long time.

I have a very old GARMIN model 300 hand held receiver. It is so far out of date, about 20-years, that it is very slow to acquire satellite signals. The last time I got it to work I left it outside and running for about 48-hours before it finally stumbled onto some satellites.

I recommend you let your old unit sit outside with a clear view of the sky and some fresh batteries for a day or two. You may find that it will eventually find satellites.

Older receivers could only track one satellite at a time and had to time share among available satellites. Newer receivers can track as many as 20 satellites in parallel. Receiver sensitivity has also been improved.

JBCornwell posted 03-30-2011 03:46 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Thanks for the offer Goldstem, but the 176 can't use the City Navigator software to "navigate" my vehicle, which is its main duty.

Thanks for the suggestion, Jim. It makes sense if that is what it needs to get a current ephemeris. It currently goes into "Auto Locate" and takes from a minute or so to as much as four or five minutes to decide where it is and what the date/time is.

I realize that isn't a big deal, but it is to me when the unit won't do what it did for years.

When it is working correctly it does everything I want it to do. If I were going on big water in a Boston Whaler as I did up to a few years ago it would be nice to get weather, but those days have become memories, and I never had the slightest interest in music when afloat, so I thank those who urge me to get an "up to date" model for their concern, but the old unit will be just fine when I get her to do what she is supposed to do.

RED SKY at night. . .

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