Hey Minh, I think someone has changed the option setting of the machine. Please control the option setting by putting RS1 (on the main print card) to 7, switch on the contact. The 2th and 3th number starting from the left side must be on 0 and not on 1. if you need to change that number, use the M button to go to the next number and + or - button to change the value. Switch the contact OFF and change the RS1 back to O, switch it back ON and see what the result is.
Regards
Marcb