Garmin 740s - GPS lock issues

[ol' boy]

The Garmin 740s is a Chartplotter for marine use.
It seems to have this painful problem of taking 45minutes to lock onto sats, which makes it useless when you launch and want to set your heading.



This is now the second GPS Chartplotter to suffer a similar problem, the last being a Navman Marine Plotter.

Both units allow for an external GPS antenna to be fitted and used.
After installing the latest firmware on the Garmin 740s, the GPS lock problem is still the same.

My question, is a GPS antenna (external) more or less the same thing across brands and platforms?
Could i try any GPS antenna to see if that helps?

This is a unit for the Garmin 740s, The OEM one is white in a mushroom shape.

[Tiny]

Mate I wish I new the answer to that, however I don't.

Another member or 2 here know their stuff on marine GPS gear & will hopefully chime in for you.

[Tiny]

had a quick look to educate myself & it appears that as long as you can attach it to the GPS with the correct connector (BNC for a 740s by the look of it), then it should be good.

Pick an antenna with the amount of DB gain you want, with correct fitting or an adapter, with the length of cable needed for your installation.

External Antennas
Six models available, MK-76, SM-76, RA-50, RA45 or RV-76. All suitable for marine or automotive use. All units (except MK-76 3m) sold with 5m of coax and mounting bracket.

	- small, light suitable for hiking and automotive use.
	- Low voltage unit suitable for most handheld GPS and GPS peripherals (eg CF gps units)
	-Re-radiating unit suitable for all GPS units without an external aerial connector, eg Garmin 12, Etrex, Magellan Meridian and eXplorist series. New model with 1-1.5m re-radiating range.
	-no longer available
	- specially designed for Marine use but will work in almost all other applications.

Also accessories:

BNC-MCX adapter cable, MCX GPS end - $29 -

MCX-BNC adapter cable, BNC GPS end - $29 -

Example uses:
Garmin 38,40, Etrex, Magellan Meridian, eXplorists range use RA50, RA45Garmin 45,48,II+ use /BNC
Garmin 12xl, 12CX, 76, BlueTooth, Magellan Colour, TravRoute Ipaq Sleeve use /MCX

[ol' boy]

Thanks Tiny, thats about what i found too.

Its been a very hard subject to read up on or search about, as not many people have GPS Chartplotters.
And those that do, have little idea, they are just end users.

I cant even find a Garmin 740s tear down with pics.
At the price of the units, i guess people are apprehensive to pull them apart.

When we turn the unit on, it is at the beach, with full view of the sky, the boat has a soft canopy, with a tubular metal frame, so it should be transparent for GPS signals.
After a lot of searching, seems Garmin as a few issues with Sat Locks across a range of GPS products.

Dam things are so expensive. And it really pisses you off when your smart phone or tablet get a GPS location in seconds! While right next to the Chartplotter.

Will try an External antenna and report back.
Spoke to Garmin, they had little to offer about from the standard, "install the latest software".... yeah yeah, did that, nothing changed.
They suggest using an external antenna, i can see the outcome will be the same though.

[Surething]

A common problem is the time in-between proper sat locks for many GPS units if the unit has been left without a backup power source for an extended period of time. The effect can be the same as a hard reset, meaning the unit has lost the satellite almanac/ephemeris data used for positional triangulation and has to rebuild it as if it has never had a fix before. That can take some time, 20 to 30 minutes isn't uncommon and longer particularly if conditions aren't ideal. Of course even if they still have the almanac/ephemeris data retained but have been moved many kilometres from the last sat fix then the next fix is going to be slower than if the position is roughly the same.

So is the unit taking up to 45 mins only if it's been without power at all for some time or does it happen even if it's been still connected to power but switched off?

I also admit to knowing little specifically about marine units, however i doubt any such unit uses 'hotfix' as in nuvi-type automotive devices. Hotfix is a software based method for the unit to remember its previous location and extrapolate from there to enable it to be ready quickly for navigation i.e. in a couple of seconds. Quite effective when combined with the 'snap to nearest road' [lock on road] feature. It may not be appropriate for marine units to 'guess' their likely position in that way, and for safety reasons they may need to get an exact updated fix by traditional methods.

Another thought is that your 740s is WAAS capable. Australia doesn't have any WAAS-type SBAS system so having WAAS enabled doesn't achieve anything except higher power usage and perhaps the unit fruitlessly searching for those dedicated SBAS satellites.

[ol' boy]

Brilliant response Surething, and it concurs with what the Garmin Rep also says.

Yes, the unit is removed from the boat each trip and stored in a locked garage (with Sounder and Navman GPS chartplotter) in a protective bag.
So it might be 1 month to 2 months between being used.
Each time it is turned on, it defaults back to the year 1989 (or similar, but you get the idea) until it can get a "sat lock" and pick up live info from the sats.

But, when it was new (2 years ago) it would turn on and get a LOCK straight away.
Now... its take the 45minutes too.

So what you say makes good sense, perhaps what ever internal power or capacitor is used might be failing after 2 years....

We might try switching the unit on one day after we have used it to see if that works?

[Surething]

Sure, it might have an charged capacitor which isn't going to power the non-vol memory for long or maybe a coin lithium ion cell which has failed. Won't be in Garmin's specs knowing them but whatever it's got has either failed or is incapable of maintaining the info for very long so like i said it's like it has had a reset. Game to open it to look? I wouldn't be for sure with such an exy unit without a detailed step-by-step.

The other option would be to keep it on a power source at home some way, cos if you find it's lost the nonvol in a day something has gone in it for sure.

[ol' boy]

We tried a simple power OFF, then straight back ON, still took a while to find the sats and LOCK.
Even though it was all working before turning it off.

Yes, i'd be a little worried to open it up, being that it is so water proof etc.

[ol' boy]

Solved

Cheap eBay GPS antenna and the unit gets a LOCK in 3 seconds!

Tested it multiple times, booting with and without antenna, every time "with" the antenna LOCK was within 3 seconds
Without the antenna, it didn't get a LOCK, even after it had just booted up with the antenna connected, so obviously it doesn't retain any information.
Strangely, you can boot it up with the antenna, then remove it, and it will stay LOCKED on.

The newer firmware seems to have also helped slightly too. Almost like they relaxed on the amount of bit rate errors or something.
As it would get a lock after 5-8 minutes instead of 45 minutes with the new firmware installed.

No idea what has happened in the Garmin unit, but it now works and hasn't become a $2000 paper weight.

This link says it all: