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I recently got the job to find out how to pass conducted EMI tests with a bad electrolytic capacitor after the rectifier in a power supply. The background is of course, that the new type is cheaper than the one used at the moment (with which the product complies to all standards). I have some experience with radiated emission of a PMSM-driver or a step-down converter but nothing so close to mains. In which way shall I make my investigations?

I should add b.t.w. that the layout of the PCB must not be touched at all.

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  • \$\begingroup\$ good luck... fixing EMI concerns post-production is expensive and hacky... Hire some EMC equipment and capture some OLD,NEW conducted CM&Diff results to gain an understand what the issue is. it might be a simple fix \$\endgroup\$
    – user16222
    Commented Jul 27, 2015 at 17:08
  • \$\begingroup\$ Hm, let me think about it. No layout changes. Likely not possible to put back the old cap again, which also translates to no change of other components. Likely means no added costs, that precludes any shielding (that would be more expensive than the cap anyways). So, how many goats and chickens do you have to sacrifice? \$\endgroup\$
    – PlasmaHH
    Commented Jul 27, 2015 at 17:23
  • \$\begingroup\$ @PlasmaHH I'm not sure goats & chickens will suffice - perhaps a cow or 2 might do ... \$\endgroup\$
    – brhans
    Commented Jul 27, 2015 at 17:42
  • \$\begingroup\$ I may use other models of common-mode choke, x-cap, inrush current limiter and rectifier diodes as long as the overall product gets cheaper and all footprints/pitches stay the same. \$\endgroup\$
    – christoph
    Commented Jul 27, 2015 at 17:59

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