Random characters almost always come from a mismatched serial baud rate or a different character set between software and printer. A faint receipt comes from the paper or a dirty print head; a truncated one, from a print width set to 80 mm while the roll is 58 mm.
Procedure
Mismatched serial port settings
On a serial link, a different baud rate or parity on each side produces perfectly reproducible random characters. The reference values are those printed on the self-test; align the software to those values.
Different character set
If only accents and symbols come out wrong, the text is right but the code page is not. Set the same character table in the software and in the printer: the list of available tables is on the self-test.
Print width and roll width
A width set to 58 mm on an 80 mm roll prints narrow; the reverse cuts off the end of each line. Check the width declared in the driver, in the software, and the printer’s physical paper guide.
Paper or print head
A receipt that is faint all over comes from poor-quality thermal paper or a dirty head. A constant vertical light stripe indicates a failing zone on the head, which is a hardware fault.
Generic driver or cable
A generic driver installed instead of the manufacturer’s sends sequences the printer misreads. An overlong or poor-quality cable produces the same symptom, but intermittently.
Check these before calling support
- The self-test prints legibly; if it does not, the fault is in the hardware.
- The roll width, the paper guide and the driver setting are all the same.
Useful terms
- 80 mm and 58 mm thermal paper
Thermal receipt paper is sold in rolls of two main widths: 80 mm for counter and kitchen printers, and 58 mm for compact and portable models..
- ESC/POS
ESC/POS is the command set created by Epson that most receipt printers understand.
- Direct thermal printing
Direct thermal printing is a process that darkens heat-sensitive paper through contact with a heated head.
- Driver and firmware
The driver is the software that lets a device talk to the operating system; the firmware is the software embedded in the device itself.
Hardware involved
- MG80 (Printers)