OK so I opened up the phone once more and had a peep at the antenna connection under the metal shielding plate that you can partly open by lifting up the little flap that secures it. That connection seemed OK. In some message I did read that it can look right but still not be fixed properly… But my connection only disappears behind my desk and is better in other places in the house .
ANyway I then cleaned the tiny contacts on the antenna cable that join it to whatever it is on the other module. This might have helped, but as the reception varies so much it remains hard to tell. All in all I have learned quite a lot about the phone and the sim cards.
Oh and, some where in settings you can follow signal strength expressed in - dB. Bad reception scores like -115dB and good reception - 95 dB, at least thats what it looks like so far.
I checked this with my sons telephone which scored similar results.
Is anyone out there familiar with these values?
ANd thanks everybody! To be honest, I have had nothing but problems with the phone since I bought it in 2015 and am used to it not working properly. Most modules have been exchanged and I am happy everytime it works…