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Edge 520/520 Plus GPS Signal disturbances during cold start

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GPS Signal disturbances during cold start

Former Member over 9 years ago

Hi, I`m having strange behaviour during cold start of unit (520, cold start = after 6+ hour of turned off device).
When powering on the device it starts to acquire the gps satellite signal, after several seconds on the outside (30-40sec) it gets with "gps ready" and the bar turns green. Shortly after that (15-30sec) while stationary it looses the signall with message "lost satellites" and searches for signal again. Next time after bar turns green it stays there. Then, after overall around 2min at beginning I can start my ride with proper accuracy. If I start ride after first "gps ready" message my track is messy and lacks accuracy (cut corners, track on buildings, etc).
This is my second unit after replacement, newest software 6.20, did master reset - did not change. BT on, connected with wahoo hr+spd+cad.

Anyone also experience this unusual cold start signal reception? Could it be the second unit with faulty gps receiver? Beside longer start times it sometimes lose track when riding with trees nearby and my segments are ruined. Other units (500, polar m450, smartphones) are keeping in same conditions pretty well.

0 Tpcorr over 9 years ago

The gps signal can be lost under heavy tree cover or in tunnels. This happens all too frequently with my Siriusxm satellite radio in my car. I rarely lose my gps signal on my 520, even though I frequently ride in heavily treed areas. But I always have the gps set to gps+glonass. If you haven't tried this yet do so and see if it solves your problem with lost signals.

The only time my 520 will drop a gps signal once it is acquired is when I'm indoors. A strategy you might try is to turn your 520 on as soon as you're outdoors and while you're pumping up your tires, getting your helmet and shoes on it should acquire the signal for the second time. You may just start out in an area with a weak signal, due to tree cover or other factors. Good luck.

Tom

0 Former Member over 9 years ago

Tpcorr, I have this "gps+glonass" setting all the times. I used to test gps-only setting, but accuraccy of tracking was noticeably worse throughout whole ride.

I tried also watching the satellite reception screen during initial gps signal searching and it looked like after first 'gps ready / ready to navigate" message, screen was full of high green bars coresponding to signal strength of each visible satellite. Accuracy was getting 50 meters and improving but then, 'lost satellites' kicks in and all green bars disappear for a second. All at once. LIke in a reset or something. After that search is started and those green bars start to show up again with accuracy starting from 120-200 meters. Unit is stationary on the outdoors during that time - no trees above, couple of blocks nearby. Entering the indoors is like you described - when using elevator it also loose signal but picks it up very quickly as soon as any window is near.

Currently I power up the device when going out to give it more time to lock the satellites. Still have to wait sometimes ~1 minute extra time with clear sky to get proper lock on.

0 Tpcorr over 9 years ago

In that case, if you're still within your warranty, I'd contact Garmin and see if they think a repair or exchange is indicated.

0 Former Member over 9 years ago

Same here - it locks first, then loses GPS and locks again in a minute. Happens every time I do cold start.
I don't do anything, just wait for another minute. Not a problem at all.

0 Former Member over 9 years ago

max-au, does your unit also happens to loose accuracy badly sometimes? I suspect this might be related. Mine edge recently-> http://imgur.com/qqMUbF8 - other units of friends I rode with - e500, m450, s5 neo - did fine. Only the 520 failed.

0 KGB_NIST over 9 years ago

I'm having the same problem. Locks to GPS then loosing signal and then locking again... Think I started to see this behaviour a few weeks ago and never before. Also only when "Cold starting". Its annoying but is best solved by waiting an extra 1-2 minutes before cycling.

Not really having a problem with losing accuracy during training but it measures way too short when doing MTB. My Suunto Ambit3 is much better when mountainbiking (frequent turning, altitude differences and occasionally some tree cover). Can be 1k difference in a 15k MTB lap (a measured Xterra track) where the Edge measures the course to 14k and the Ambit is spot on.

0 Former Member over 9 years ago

max-au, does your unit also happens to loose accuracy badly sometimes?

No, never had any issues with that.
I had another (totally different) issue with speed sensor. It reported half/third/zero of an actual speed when riding specific portions of a highway with metal barrier in close proximity. I was not able to find the root cause. Ended with simply disabling auto-pause, so at least is stopped pausing my ride.

0 Former Member over 9 years ago

Thanks for information. I started discussion with garmin support and meanwhile as a workaround I wait bit longer before unit can be used correctly.

Also more observations of satellite-view makes me think there might be some software issues with gps chip. At least it could explain all odd behaviours. If the gps chip issue (crash/memory leak/bad pointer/bad data/I-O error/memory error) makes it restart during initial cold satellite search it would lead to 'lost satellites' message because this step take longer time (up to 45 seconds according to specification for cold-start). If the issue happen mid-ride, restart would not be visible to user because hot-restart is instant on 520. Wrong position could be side-effect of gps chip restart - like bad readout or wrong data.
It would be good if there would be some sort of internal on-unit log of crashes or gps-chip restarts. That could prove/deny my theory.