Problem with lcd 1602

[liyuanyuan-rudel]

30_i2c_lcd1602.py

LCD1602.init(0x27, 1) # init(slave address, background light)
Until this line, all things are fine, because when I change it to LCD1602.init(0x27, 0) background light is closed.
So I think the address and connection is right.

but the characters are not showing on the screen.
Could you please check it？