I'm sorry for the inconvenience.
According to the situation you described, if there is a signal when you don't make a phone call, but this problem appears as soon as you make a phone call, it may be caused by signal factors, system anomalies or communication module anomalies;
In view of the signal factor, I suggest you try to use it in other fields; You can also try to replace another SIM card to see if the problem still exists, so as to eliminate the problem caused by a specific SIM card.
In view of the abnormal system, it is recommended that you try to restore the factory settings. You can find the corresponding options through system settings-backup and reset. Since restoring the factory settings will erase the original data information, it is recommended that you make a backup first, which can be synchronized in the cloud through cloud services.
If the problem still exists, we suggest that you contact Lenovo's authorized repair point in time and ask the engineer to check and repair it. You can visit/Lenovo/WSI/station/servicestation/default.aspx? MIDH queries the nearest site. The business hours of maintenance stations are generally from 9: 00- 18: 00 from Monday to Sunday, except holidays, and local stations will adjust slightly according to their own operations. I suggest you call for detailed consultation before you go. Please refer to it.
For more information about Lenovo products, please visit Lenovo Service and Support:/default.aspx.