Because of some problems after installing android 7 through OTA update I decided to roll back to some older version. After trying all ROMs available at needrom.com I managed to make it work with 2016_10_25 version. Both IMEIs got reset to 111111111111 and 222222222222 but finally i restored them using some "write imei" application.
The problem is that GSM signal is much weaker now at both SIM slots compared to other phones (using the same SIM cards). I tried a couple of different SIM cards - in other phones signal strength is around -70dBm, in my BV6000 it is usually weaker than -100 dBm or totally dead.
Is it a software problem, or is it possible that I damaged some electronic part of radio/antena, for instance by static discharge while touching the inside of the phone? (I opened the phone because I had to fix the proximity sensor issue).
Edit: It seems my phone can only see 2G/EDGE networks now. It is strange, before it used to see 3G net with strong reception as well. Any solution?