Megadrive 2 official SCART cable (MK-1637-09)

This is not a good cable, not good on modern TV's anyway. Loud buzzing sound from lack of shielding.

 

This is quite a well known issue - its not a problem with the shielding, its actually due to a poorly designed DC boost regulator circuit inside the SCART plug:-

This French article explains it in greater detail:-
http://www.segakore.fr/articles/mod_cable_rgb_md2.html
You can simply disable the DC boost regulator, however this disables SCART switching.

Alternatively you could adjust the circuit/SCART wiring to use just the 5V line for both SCART switching pins (with a 180ohm resistor inbetween pins 8 and 16)

Lastly I believe you could even repair the original circuit using better component values (I saved this picture from somewhere)

 

Thanks for the info. I have just checked the page you linked and (translated to English) found that the relevant traces inside the scart connector have already been cut.

 

Well you could try the other fix linked at the bottom of the previous guide:-
http://www.obsolete-tears.com/reduire-un-peu-plus-le-bruit-du-son-dune-megadrive-2-dossier-114.html

Or heres a fix I just made up - this should completely isolate the DC boost regulator circuit from all other connections, and disable SCART switching entirely.

Just cut the two ground traces shown with red crosses, then isolate the 5V pin by cutting another two traces (This mod is untested, so attempt at own risk)

....However, to me the question becomes at what point is it still worth using the official cable? If it requires so many modifications, at some point the 'official' branding no longer means anything anymore. In my opinion it may be worth buying a custom cable from here:-
https://www.retrogamingcables.co.uk...e-2-sega-genesis-2-rgb-av-scart-cable-tv-lead
But the choice is yours!

 

I wasn't aware of these issues, if I had known then I probably wouldn't have bought it. I checked the page you linked to yesterday and I thought about doing what you have described today in isolating the regulator. I might try taking the 5V and connecting pins 8 and 16 so I can at least have auto switching. I basically just want a working cable now, I'm not bothered about the "official" status of it. I already have some aftermarket modern cables that work better than this one.
I also tried the additional alteration in removing the capacitor and putting new caps on the audio lines, it did reduce the buzz a little bit but not entirely.

 

Well if you manage to get rid of the buzzing (Maybe try the fix I posted?) then we can work on getting SCART auto switching back.