Hello ! Recently I had a problem with one of the sim slots and I took my phone to the service centre. I took it back, but obviously they have done something to the wifi antenna, because the signal now is very week, even right next to the router. The problem is not in the router itself. I don't want to get my phone back to the service centre, because of many reasons. I understood that the problem could be in the wifi antenna, but I don't know where it is, in order to try to at least clean it. Can you help me? Thanks!