A yarn quality assurance method and a yarn processing machine set up for implementing the method according to the invention is proposed comprising at least one feeding spool receiver 24, 30 set up to receive respectively at least one feeding spool 20, 29 from which yarns can be taken off, and a multifilament yarn manufacturing unit 5 to which yarns are supplied from the feeding spools 20, 29 via thread runs with respectively one thread tension. According to the invention, a thread tension regulating module 25 with a thread tension sensor is arranged in at least one controlled thread run 1 between the relevant feeding spool receiver 24 and the multifilament yarn manufacturing unit 5, wherein the thread tension regulating module 25 is set up to derive a control value from a thread tension measured by the thread tension sensor and to keep the thread tension constant in a predetermined thread tension range.