(Turn over warn: turn over switch is effective)

Error solution steps
Check the impedance between two legs of mercury switch U5 when the main board is in upright position: around 11.7K; If the main board is in horizontal position the mercury switch will be short circuit and the impedance: 0Ω
Check the impedance of C51 on main board: around 10K; supply power of 80V by isolation transformer, the voltage is:3.2V
If the mercury is not working, access control box’s parameter interface,set the parameter No.10 to value 1.