Garmin 72 gps deteriorating ability to pick up satellites

[SAWDOC]

My garmin handheld gps 72 has worked well for several years . Recently it seems to take an age to locate satellites. On a recent trip a crew member had an identical model much newer than mine which found satellites in no time while mine was still clueless.
my question - do gps devices deteriorate over time in their ability to locate satellites or is their another factor I may not be considering? In the case above, both gps units were side by side above decks on a reasonably bight day.

 

[elton]

Does it take ages to locate satellites every time you turn it on, or just that time?

If the former, it's likely the cmos memory battery is failing. If the latter, it was probably acquiring the almanac, which takes a long time if you've travelled a long way since it was last used, or had it turned off for a long time.

 

[TQA]

Can you change the cmos battery in a 72/76/78?

 

[SAWDOC]

In the very recent past, I would say every time rather than just one occasion. Never heard of CMOS memory (loss) - must check that out.

 

[elton]

Can you change the cmos battery in a 72/76/78?

Garmin will replace the so-called "memory battery" for a price. It can be done at home, if you really know what you're doing.

 

[lw395]

Garmin will replace the so-called "memory battery" for a price. It can be done at home, if you really know what you're doing.

It's not hard to replace the battery if you can solder and get the unit apart.
One thing which may help is to leave the unit powered on where it can receive signals for a long period, at least a day, preferably longer.

Over time, the reference crystal in a receiver drifts. The unit calibrates this against the satellite signals, but only very slowly, so may not happen properly for old units that are used occasionally for short periods.

I made my GPS120 work a whole lot better by calibrating the reference against a Rubidium standard. There was a sub-menu somewhere, which showed what the GPS thought its reference was, down to a few parts per million.

GPS's also go deaf over time for other reasons, so maybe they are just something you should write off over a few years?

But I think leaving it powered for a week is worth a go, assuming you have a power lead.

 

[elton]

Over time, the reference crystal in a receiver drifts. The unit calibrates this against the satellite signals, but only very slowly, so may not happen properly for old units that are used occasionally for short periods.

I've never heard of that. The crystal depends upon its physical mass for its frequency; as that can't change, I don't see how the frequency can drift. Crystals are used as frequency references in all manner of devices, from clock to radios to ultrasonic "tape measures" and televisions. They can work reliably for decades, and I've never seen one fail because of frequency "drift". Have you got a reference?

 

[lw395]

This isn't the best paper I've seen:
http://www.isotemp.com/wp-content/uploads/2011/04/Crystal-Oscillator-Aging.pdf

I'm sure there was some stuff on the web about the GPS 120, but that was some years ago now.
I no longer have that GPS.

I've noticed that old GPS's that have been in the cupboard unused for months or years acquire very slowly, even when presented with a boosted GPS signal.
GSM phones also correct their frequency reference, but that's a whole different anecdote.

 

[elton]

This isn't the best paper I've seen:
http://www.isotemp.com/wp-content/uploads/2011/04/Crystal-Oscillator-Aging.pdf

I'm sure there was some stuff on the web about the GPS 120, but that was some years ago now.
I no longer have that GPS.

I've noticed that old GPS's that have been in the cupboard unused for months or years acquire very slowly, even when presented with a boosted GPS signal.
GSM phones also correct their frequency reference, but that's a whole different anecdote.

Thanks for that. It rings bells now. I have a dim recollection that the crystals used in the Redifusion televisions I used to repair, were artificially aged before installation, but I don't know to what extent this extended the expected stable lifetime. I still question whether the extent of drift could adversely affect the functioning of a GPS reciever, but I'll take your word for it

 

[Allergy]

My garmin handheld gps 72 has worked well for several years . Recently it seems to take an age to locate satellites. On a recent trip a crew member had an identical model much newer than mine which found satellites in no time while mine was still clueless.
my question - do gps devices deteriorate over time in their ability to locate satellites or is their another factor I may not be considering? In the case above, both gps units were side by side above decks on a reasonably bight day.

I have the same 72 as you with the same symptoms. I phoned Garmin here in the UK & explained the symptoms. The bloke in the Service Dept said that all you need to do is to reboot. He then sent me instructions via email & it's back working ok. Sorry, cannot find the piece of paper.

 

[Trundlebug]

Over time, the reference crystal in a receiver drifts. The unit calibrates this against the satellite signals, but only very slowly, so may not happen properly for old units that are used occasionally for short periods.

I made my GPS120 work a whole lot better by calibrating the reference against a Rubidium standard. There was a sub-menu somewhere, which showed what the GPS thought its reference was, down to a few parts per million.

I replaced the Rubidium with DiLithium crystals but eventually they too burnt out as they couldnie tekkit anymoor captain

 

[lw395]

I have the same 72 as you with the same symptoms. I phoned Garmin here in the UK & explained the symptoms. The bloke in the Service Dept said that all you need to do is to reboot. He then sent me instructions via email & it's back working ok. Sorry, cannot find the piece of paper.

https://support.garmin.com/support/searchSupport/case.faces?caseId={2a1ec320-5168-11dc-4ec8-000000000000}
back up yer waypoints first!

 

[SAWDOC]

https://support.garmin.com/support/searchSupport/case.faces?caseId={2a1ec320-5168-11dc-4ec8-000000000000}
back up yer waypoints first!

Thanks for posting the link - hopefully that will be useful. I have several years of useful routes nd WP 's in th garmin and afaik the only means of backup with the 72 is to manually transcribe . It can not be connected to a pc.

 

[lw395]

Thanks for posting the link - hopefully that will be useful. I have several years of useful routes nd WP 's in th garmin and afaik the only means of backup with the 72 is to manually transcribe . It can not be connected to a pc.

I seem to recall at least one GPS where the NMEA port was on the pcb, just not taken to the case.
Just a thought!

Otherwise, bit of a sod, at what point do you give up on your waypoints to attempt improved reception.
Also removing the cmos battery may lose the waypoints?

 

[SAWDOC]

That master reset seems to have done the trick. Fortunately I had a list of WP made already using another program so hopefully back in full operation.

 

[garvellachs]

It can be connected to a PC, unless it's so old it pre-dates the feature. Just need the right lead.

 

[TQA]

The free GPSU usility lets you download and upload waypoints etc.

Works for me.

 

[davidpbo]

My Garmin GPS MAP 76 connects to a PC via a 4 pole connector on its back, 2 poles carry power and 2 Data.

Don't kknow whether the 72 is the same.

I have a dedicated cable propably bought as an extra.

Unfortunately it requires a serial port connector on the PC which a lot don't have now adays. USB to serial adaptors are available. A bit of jigging with port numbers etc. may be required.

 

[TQA]

My Garmin GPS MAP 76 connects to a PC via a 4 pole connector on its back, 2 poles carry power and 2 Data.

Don't kknow whether the 72 is the same.

I have a dedicated cable propably bought as an extra.

Unfortunately it requires a serial port connector on the PC which a lot don't have now adays. USB to serial adaptors are available. A bit of jigging with port numbers etc. may be required.

72 works the same.

 

[davidpbo]

Should add that with appropriate software computer can talk to gps cant remember what can be downloaded and uploaded. Certainly maps on mine and assume waypoints.