I have a problem with my sim2, it cant reach any kind of signal, but sim 1 is good. Now thanks God, my problem solved.
For who has problem with signal.
Try to call *#*#4636#*#*.
Choose your sim.
Look at set preferred network type.
Change to TD-SCDMA, GSM/WCDMA and LTE.
Hope works.
Edited: mi5