1. Vertical black lines with the same width of more than 1 cm appear on the printed document and the drum core at the same time: This is a problem with the scraper, causing the powder on the drum core to not be scraped cleanly.

2. Vertical thin black lines appear on the printed document: usually the scraper and the small scraper on the edge of the scraper are stuck with dirt or scraps of paper.

3. Horizontal black lines appear in the printed document: Usually the magnetic roller in the toner cartridge has accumulated powder, just turn it a few times and it will be fine.

4. If there is obvious gray background on the printed document: usually there is a problem with the drum core or toner.

5. The color of the printed document is uneven. There is a famous saying: From the outside, the toner can still be seen on the magnetic roller. If there is powder in some places on the magnetic roller and no powder in some places, it means that the toner cartridge of the toner cartridge has been exhausted.

6. If the printer prints a blank sheet of paper: first check if there is any problem with the printer. If there is no problem, it means there is something wrong with the toner cartridge during assembly.