[How-to][Hardware] Fix XA2 GNSS(GPS): Let's Try harder

After some introduction and considerations, I’ll share here the way I renew XA2 GNSS signal path from the motherboard through the antenna to the mysterious top cap (part of the antenna?).

The GNSS term is used here, as it stands for Global Navigation Satellite System, including GPS(US), Galileo (EU), GLONASS (RU), BDS (CN)…

Hardware, why?
##############
Because there are much differences reported between XA2 GNSS capabilities, I believe the Sony Xperia XA2 can have some Hardware problems regarding GNSS.
These supposed problems are bad contacts caused by mechanical pressure, dirt and eventually corrosion (aluminium top cap contacts becoming black).
Here is a method to eliminate, as much as possible, these HW doubts. To avoid, as well, the HW/SW debate: Once fixed, no doubt, we can concentrate on software issues (well…how?).

I did this on 3 XA2 and I noticed a clear improvement in sat signal reception, especially on the last one, these days, which even turned to a no-GNSS device, even with @nekron’s patch.It now has very good results and TTFF was very short in the two tests I made since repaired.
I am waiting to make some more tests to report in a further post.
But again: this is not solving the problem completely. Better reception, faster fix but after some time, TTFF inconsistencies may occur.
It is possible too, that touching the GNSS chip antenna’s path does reset something and has nothing to do with what I propose here. I am still groping. False positives are possible.
If my objectivity is hijacked by my beliefs, please tell.

“Android has no such problems”
##############################
Such XA2 GNSS problems are not reported under Android.
This would tend to indicate there are no HW issues.
I believe it is not so simple.
Android possibly has much more assistance to determine position, such as phone network, wifi access points, eventually bluetooth proximity, towers positions which are durable and possibly (my own personal assumption only) included with Android.
I have no doubt that Android maker has a big power to collect data to help location even with a bad GNSS signal. And who knows, as said, some helping data could even come with Android itself as a base before actual up to date data are collected.

Fix, and then?
##############
Then, we have to make more tests in strict conditions with precise reports.
We really are walking in the dark regarding this GNSS issues with very few visible helpers and few objective things to test.
Conditions of GNSS use are very diverse. GNSS technology is complex and conclusions are hard to draw.
I am not a scientist and I know that my beliefs can influence my objectivity. Please underline contradictions and incoherences if necessary.

Extract the good juice
######################
The other GNSS threads contain lots of precious reports and remarks. Ideally, these pieces of informations would have to be extracted and grouped.
But they also have a not so good signal/noise ratio regarding tests results IMO. Much lightweight statements are made (by myself included) and useful conclusions are hard to pull.

Think harder
#############
Please read the following pages before to post:
https://www.measurementsystems.co.uk/docs/TTFFstartup.pdf
https://ozzmaker.com/take-long-get-gps-fix/
https://novatel.com/support/known-solutions/gnss-ephemerides-and-almanacs
https://www.e-education.psu.edu/geog862/node/1739
https://gpsbeam.com/what-is-time-to-first-fix/
https://gpsbeam.com/assisted-gps-agps/
These pages were provided by @NodaUK here: https://forum.sailfishos.org/t/hardware-xa2-gps-trial-to-fix-it-for-debuging/10133/28

Further informations:
https://www.e-education.psu.edu/geog862/node/1405
https://en.wikipedia.org/wiki/Time_to_first_fix
https://en.wikipedia.org/wiki/Satellite_navigation_device


Some theory
############
Now you have read the above pages :-), here is a tiny summary of major principles and terminology.

  • TTFF: Time To First fix
  • A-GNSS (aka A-GPS): Satellite data received by cell towers which transmit them to phones’ GNSS (Assisted GPS aGPS -).
  • Almanac: Orbital Datas common to all satellites. Contains incomplete ephemerides to generate a list of visible satellites. Each Sat has and can transmit the Almanac. Usually updated every day. Download time: 12.5 minutes. Validity: 180 days.
    “If the GNSS receiver has some left over almanac and position data,[…] the receiver might begin by knowing the time within about 20 seconds and its position within 100km or so, and this approximate information helps the receiver estimate the range to satellites […] to those likely above its horizon rather than wasting time on those below it. Limiting the range of the search decreases the time to first fix.” (The Almanac, Time to First Fix and Satellite Health | GEOG 862: GPS and GNSS for Geospatial Professionals)
  • Ephemeris: Download time: 30 seconds. Unique and satellite specific orbital data. Validity: 4 hours (from when it was computed!).
    No almanac nor ephemeris = cold start = minimum 12.5 minutes in perfect conditions.
    Wrong: “Cold start happens after 24 hours”. From what I understood from the documention, a cold start happens when the almanac is too old (> 180 days) OR speed over 90km/h OR +100km (60 miles) away from last fix.
    In that case, most of the reported cold starts were not cold starts…

Hypothesis:
###########
What causes of our sorrows with XA2 GNSS could be?
-Only hardware? (as users, inc. Jolla, report having no problems)
-A wrong initial position approximate (The GNSS receiver needs to know where it is, to eliminate unnecessary satellites search (sats located under the horizon are not useful!))
-“Blocked” old Almanac/ephemeris data, preventing fresh data to take place.
Your thoughts?


Practice
########
Let’s go back to initial subject: renew the contacts along the GNSS antenna’s signal path.

We’ll have to open the device.
Here is not THE right method. Just the one I found.
You may harm your phone. Try at your own risk.
Be patient, don’t be in hurry.
Be concentrated.
Be optimist.

Read the whole post before you begin!

Important: Don’t remove the top cap!
To pull out the antenna board, I noticed it is much easier and less dangerous for the path’s last tiny contacts to keep the top cap in place.
There is no use to remove it and is a pain to replace.

First, remove the back cover.
The idea is to unstick the glue with a plastic board.
I use an old credit card. I file the edges to make them thinner. This allows to get easier under the covers.
To avoid using a metal blade several time, we will use parts of packaging window (correct term please?) as entry for the card, as it often slip off the cover.


pic1


Use a cutter. Delicately thread the blade under the lower corner. Don’t go further!
Be very careful as the aluminium bottom cap marks as soon as you touch it with the metal blade.

pic2


Slide a part of packaging window behind(under) the blade.

pic3
resized_600-20220605_151454
The same with the credit card.

pic4


Thank to my graphic designer talents :slight_smile: , you can see the zone where you should not go too deep under the cover (red). Be especially careful on the left side where the FP reader plug is located. Be careful with the camera too.
You can’t go neither under the green “circles” as little prominences go from the cover to the phone’s frame.

pic5


The glue is all around the phone near the edges. Unstick the cover and as soon as you freed a portion, thread a part of packaging window under that portion to get this.

pic6


Now, with the help ot the card and your feeling, unstick more, slightly, all around, until the cover moves.

pic7


Be careful: when it will release, the cover might go in one big move and you risk to break the FP reader’s plug/cable.

pic8
resized_600-20220605_152645
Unplug the plug. Use wood or plastic stick.

pic9




Unscrew these 3 screws (yellow marks, see below):

pic 10


The black board you just unscrewed is the antenna board.
Go slowly as there is some grounding metal tape glued. try not to soil it so you can stick is back later.
Lift it from below. You’ll have to bend it a little as there are 2 clips (approx where i draw the yellow circles in the previous pic) holding it.

pic11
resized_600-20220605_153707
Free the board all around.
Be delicate and slow when you arrive on the top. Here (green mark) are the very fragile spring-blades contacts that connect the antenna board to the top cap. Dont force them and remove slowly.
(If, by unluck, your top cap is not present any more, you’ll have to push on each spring-blade from the top of the phone to allow them freely to go out the holes)

pic12
Below a pic where you can see the spring-blades contacts:
resized_600-20220605_160229
Fragile spring-blades contacts to take care of.

pic13
resized_600-20220605_154142
Here we are.
But take care not touching/soiling the camera and it’s glass and think of verifying it has no dust when rebuilding. Don’t blow with your mouth as it might send some regrettable drops! Use a photo air pear.



Cleaning, straighten up

pic14
resized_600-20220605_160632
Very slightly straiten up the contacts. I insist: slightly, like their position gains 0.5 or 1 mm.
Dont unfold the thin part but take them at their base. Our GNSS one is the one near the jack plug.
Do the same for all contacts: clean and straiten up a little (picture below).
Except for the ones linking with the back cover, as they are complex and don’t seem to be smashed (the twins, near the battery and battery plug).
Also
Clean them with isopropyl alcohol, benzine or anything leaving no deposit (knowledge gap here, please correct me). But no acetone or other which will make melt the plastic.
Depending on the liquid you choose, hear a breathing mask.

pic15
resized_600-20220605_154136
Here are all contacts. Main board to antenna board, Main board to back cover.
As the phone connection still works without the antenna board, I suppose these are the wifi, BT etc. The GSM antenna is perhaps located at the bottom of the phone.
The contact interesting us mostly is the pink one: the GNSS one.

Last point but important IMHO (I forgot to save some pics in the phones cloning process, sorry):
Also clan the top cap’s four pads touching the contacts that you can see in the pic 12 and 14. You will see they have become black (aluminium corrosion?).

That’s all, I think.
Revert the steps to rebuild the phone.
And don’t forget to check that the camera is clean before to set the antenna board.

15 Likes

Excellent how to. Well written for someone whom I suspect English isn’t their first language. I will PM you a couple of suggestions on phrases/words.

I pulled my XA2 apart today and checked and cleaned the contacts. After checking everything I’m still somewhat skeptical. It’s too early to know for certain whether there’s any improvement.

Thanks again for doing a good job on the write up. For me all I needed to know was which contacts were for the GPS, but overall avery good description.

Thank you, indeed, English is not my mother tongue.
Yes, if you have advices or remarks, I take them with pleasure.

After talking with another user who cleaned the top cap contact pads only, it will perhaps appear they are the most important.
As it is aluminium, which seem to become oxidized / have a blackish tint, it might be the part that ages the least well…
But anyhow, I’ll be curious to read your results!

I have been bolder: I have removed the top cap! Now the strength of received signal is much higher and I get a GPS fix in less than 30s without any other help.

1 Like

So is the metal top of the XA2 the actual GPS antenna then?

Just to avoid risking too quick shortcuts: Removing the top cap is not a solution in itself.
But yes, It can be a measure that helps when the top cap is not working as it should.
Some other users noticed it in the big GPS thread as well.

But a good working top cap is even better than no cap in my understanding.

The experiment below, (from here), tend to demonstrate it:

The aluminium top cap is not exactly the antenna.
I am not a specialist but I understand it as a part of the antenna system.
I figure that the main part of the antenna is the black antenna board that was described in the first post.

What still sounds strange to me is that 4 antennas paths (probably WIFI, BT, GNSS and ???) are linking together in this top cap.

If all the antenna are connected to the top cap then this sounds like it is simply a common zero volt ground, nothing else.

The way to confirm this is to see if there is a further chunky connection to a bus bar on the motherboard which eventually connects to the -ve side of the phone battery.

Sorry, do I understand correctly what you do mean: to check if the neg pole of the battery / ground is related to the top cap through a path on the motherboard?

Someone with an opened XA2 atm? :–)

Yep, you got it. All electronic circuits operate with reference to a ‘ground’ voltage. Mostly this is a fixed zero volts but it doesn’t have to be - some ‘grounds’ are floating voltages. Often in older equipment you get earthing faults where there has been corrosion (e.g. Electronic faults in cars) - especially where you have mixed metals with different electrical valences in contact with each other. The metal with the lower valence becomes sacrificial and corrodes due an electrolytic reaction. With aluminum and steel it would be aluminum that would corrode lrading to an unreliable electrical contact. So, an earthing fault could be a contributory factor maybe.

1 Like

And this is the case between top cap and what i (should?) call spring-blades contacts.

Two weeks ago, I was fed up with xa2 gps issue.
I was unable in my car, after 20 minutes to get a fix.
And, outside of the car, I got a fix, but with difficulty, with few satellite in use.
So I decided to do something.
I followed last @ric9k tutorial, and removed the top cap. Under it, there was a lot of dust. I cleaned the internal face of both cap and phone, with solder flux cleaner.
Immediately after, I enabled the GNSS receiver, and got a fix very quickly, less than one minute, with about 12 satellites in use.
I used my phone without top cap during about 10 days, and and GNSS receiver was fully functional during this time. I also noticed no issue with BLE, Wifi, nor GSM/LTE connectivities.

I would say that the aluminium to cap, a the track under it, is not really an antenna, but maybe a part of it.

On Tuesday this week, I glued the cap only with double face tape (quite strong), only for test. GNSS is still functional. Yesterday, I got a fix, in 57s, with 17/40 satellites in use.

It would be interested to see to what the four contacts under the cap are connected to.

My XA2 is my daily driver and only phone, so I don’t really want to do that. Maybe I will checked if I can find a second hand one.

2 Likes

We could imagine that this is a kind of reference plane for antenna., but usually this is only needed for 1/ wave antenna, and I don’t think there is such antenna in the phone

I did some tests by putting paper tape on the contacts, one by one, between the motherboard and the antenna board until the GNSS was not working, to determine which it was (near the jack) but don’t remember the rest…

Well yes, but for corrosion to be anything serious in this case you would need an electrolyte - the typical one being water and salt … From a sweaty ear perhaps :laughing:

Yeah, or some thunder arriving on the top cap :–)

I’ve reverted my XA2 back to android and gps seems to find a fix within seconds. The test was at home, no sim, wifi on.

Yes.
But these questions from first post are still open:

For me there’s also the question as to why the XA2 on SFOS can ‘see’ so many satellites very quickly but then fails to use them for such a long time. GPSinfo regularly shows up to 20 satellites in view within a minute or so and can locate them in the hemisphere, but then sits with zero satellites in use for up to an hour on occasions. With my admittedly limited knowledge I would have thought that if there was an antenna problem the phone wouldn’t be able to pick up the satellite signals at all and therefore wouldn’t even see them, let alone use them.

And, I believe this to be the case, we’re only talking about issues related to the time needed to get the first lock. For me, on both my SFOS XA2 phones, once that first lock has been achieved - be it in 20 minutes or an hour, that lock remains rock solid from that point onwards with the only signal dropouts being when I drive into a long tunnel, walk under heavy tree cover, or I’m well inside a large building - all standard reasons for GPS signal loss on any phone. Again, if it was an antenna problem you’d surely be having signal dropouts all the time, not just related to first lock conditions - and this simply isn’t being reported by users.

So whilst it is of course always a possibility that individual phones could have antenna connection issues causing a problem, I still don’t believe is the problem.

1 Like

I’m also interested why certain people on this forum say that GPS works perfectly on the XA2 day-in and day-out with an almost instantaneous first fix 100% of the time. They have absolutely no problems at all. At first sight these claims hardly seem credible in the light of the widespread and almost identical reports of issues affecting everybody else that we have been discussing. So why?

  1. Do they keep GPS active all the time, or use it so regularly that cold start conditions hardly ever apply?
  2. Do they have a more recent or different motherboard to the rest of us (manufacturers sometimes make electronic component and/or design changes throughout a product’s life due to availability issues, cost considerations, etc)? I have two old Blackberry Z10 phones - same model but different motherboard designs.
  3. Do they have a different regional variation of the XA2 to those suffering problems? Whilst Apple seem to produce a ‘world phone’ suitable for all markets, Sony do seem to produce multiple regional variations.
  4. Did they flash to SFOS with a different firmware/Android version (point version update) to the rest of us which had different, more recent or improved device drivers?

or what?

Sadly, I am now thinking that this is so complicated that a permanent fix for all (individual hardware issues affecting a phone aside) is probably beyond our reach - or indeed that of Jolla now - because if it is at least some of the above it will be beyond our power to change.