Vertical lines on a laser printer output are usually caused by a faulty or empty toner cartridge, a dirty or damaged drum unit, or a clogged or obstructed laser glass. According to the web search results, some possible steps to troubleshoot and resolve this issue are:
Check the toner level and replace the toner cartridge if it is low or empty. Remove the toner cartridge and inspect the drum unit for any signs of damage, such as scratches, cracks, or toner buildup. Clean the drum unit with a soft cloth or replace it if it is damaged. Locate the laser glass, which is a narrow strip of glass under the scanner lid or inside the printer. Clean the laser glass with a lint-free cloth moistened with water and remove any dust, dirt, or debris that might block the laser beam.