Had a problem with Bluetooth and GPS after a couple of weeks of use. Bluetooth range <20cm and weak GPS reception. Suspected the antenna so I decided to have a look.
Removed 4 screws at the back. Lifted the back off, note the back is sealed by a fine glue strip all around and the strip will probable be destroyed so water/dust seal will not be effective after opening.
Here you see the inside. Note the speaker port on the left hand side as I saw somebody wondering where it is.
As I was going to remove the wristband to have a look at the antennas I had to get to the antenna connection so the next thing I had to do was removing 2 screws and then I could lift up the SIM/charger port/pulse rate sensor with the battery.
BEWARE: this unit is connected to the main board by 2 flat cables at one edge of the unit. Don’t break the cables!! There are connectors on the cables so the unit can be disconnected but it can be difficult to connect again if you don’t have the right tools and steady hands.
The antenna connectors (and the flat cable connectors are under the black ‘felt’ strip running around the watch interior. Lift it up over the antenna connector and the connectors can then be disconnected with tweezers or thin nose pliers.
The GPS/WiFi/Bluetooth antenna is in the shorter wristband and the GSM antenna in the longer. Remove the 2 screws holding each wristband and lift the wristbands off the watch.
The antennas are hidden under rubber flaps on the inside of the wristband. Bending the wristband 180° at the inner seam of the flap and running a sharp edge of a small screwdriver back and forth over the elastic glue exposed I was able to break the seal until I had a flap which I could peel back slowly until I exposed the soldered connections. Now I was able to examine the antennas and measure the cables.
Assembly is
fixing the wristband
Connect antennas (and flat cables if disconnected)
Getting felt down over the connectors
Flip back part down and make sure the flatcables does not get disconnected and fix with 2 screws.
Close lid and fix with 4 screws.
Unfortunately this teardown and rebuild didn’t have the desired results. Still BT range extremely short and GPS barely works in ideal situations. Was all right when I got the watch but after some weeks the reception was intermittent and gradually got worse. Antennas and connections seems OK. So either more serious teardown to see if there is some bad connection from antenna to the receiver chip and resolder every connection in the path or just live with it (and get a new watch after some months). At least I know now something about what I should look for.
icebear have you tried to connect the antennas without closing the watch to see if it works better, i know that before the updates everything worked well but did’nt have the chance to upgrade to v2.5 so not sure, what is weird that also wifi and bt ranges were short.
along with other degrees in computer science and maintenance amongst other degrees. 
