How to rectify a faulty MC conduction emission motion controller?

To rectify the conducted emissions issue of the motion controller MC, it is necessary to locate the noise source and coupling path. Use a spectrum analyzer with LISN to measure the frequency points exceeding the limit. A common source is the switching power supply; check if its input filtering is sufficient, and try increasing the inductance of the common-mode inductor or replacing it with an integrated filter module. Check the decoupling of other high-frequency circuits inside the module. Noise may be coupled through common-ground impedance, requiring optimization of the PCB grounding system. Use ferrite rings of different materials on the power lines to observe which frequency bands are effective, and add targeted filtering components. For specific narrowband noise, it may be clock harmonics; spread spectrum analysis of the clock source can be performed. Rectification measures may include: increasing the capacitance of the X capacitor, increasing the number of turns of the common-mode inductor, adding decoupling capacitors to the chip power pins, optimizing the grounding design, and adding a secondary filter at the DC output. Retest after each modification, observing the changes in the conducted emissions curve, until all frequency points are below the limits with sufficient margin.