I. If the grounding is not good it will affect the effect of the power supply filter
II. Reasons why the grounding is not good it will affect the effect of the power supply filter
The filter has a bad lap between the case and the chassis (with insulating varnish); at the same time, the grounding wires used are longer, which will result in the deterioration of the high-frequency characteristics of the filter and reduce the filtering performance. Due to the long ground wire, the distribution inductance of the wire at high frequencies can not be ignored, if the filter lap is good, the interference signal can be directly grounded through the shell. If the filter case and chassis between the poor lap, equivalent to the filter case (ground) and chassis between the existence of a distributed capacitance, which will lead to filter ground impedance at high frequencies is larger, especially in the distributed inductance and distributed capacitance resonance frequency near the ground impedance tends to infinity. The effect of poor filter grounding on filter performance is shown in the figure.
From the figure, it can be seen that due to the poor grounding of the filter, the ground impedance is large, and a portion of the nuisance signal can pass through the filter. In order to solve the poor lap connection, the insulating paint on the chassis should be scraped off to ensure that there is a good electrical connection between the filter case and the chassis.