How to unlock and fix the B300 bracket of Lenovo consumer machine

The B300 bracket is locked to 90 ° and cannot be adjusted. How can I unlock it?

Procedure:

The machine has a lock button, which can be locked at 90 degrees.

1. Find the lock button on the bracket behind the flat machine;

 

2. Unlock in the unlock direction. If the lock may be slow for a long time, you can try to break the bracket up to reduce the lock resistance, you can easily unlock.