1. The printer cable is faulty and causes garbled printing. Sometimes the printed cable and its interface components are broken or short-circuited, which may cause garbled printing. You can check if the printer cable is faulty by running the command "dir> prn" under MS-DOS.
2. If the printer hardware is faulty, you can use the printer self-test (the self-test methods of different brands of printers are different, please refer to the printer manual) to determine whether the printer is faulty. If the printer is indeed a problem, it can only be fixed.
3. The printer has insufficient memory. When the print file is too large, garbled characters may appear. The best way is to expand the printer's memory, but this is rare, mostly in the early memory of smaller printers.
4. The motherboard parallel port (print port) is abnormally damaged by printing. This is rare. The best way is to not use parallel port printing for USB cable printing. Of course, if the printer or host does not have a USB port, it can only repair or replace the motherboard.
5. The I/O control chip on the motherboard is damaged. In fact, this situation is not difficult to distinguish, because the damage of the motherboard I/O control chip often brings many complicated situations, and many input and output devices will be affected. Solve only repair the motherboard!
6. The print port is excluded (can be seen on almost all motherboards), and sometimes the resistance value changes due to external factors, printing garbled. You can solve the problem simply by replacing the new one.
7. When printing with the switch box, garbled characters may appear. Replace the quality of the switch box or use the switch box for printing.