This is keeping me up at night

[Tempur]

Dear MB enthusiasts,

I own a Mercedes 280SLC from 1979 which came with its original Becker Mexico (374) installed including the so-called “Verkehrskurier”. The radio is emitting noise from the engine and electrical components and I cannot find a way to get rid of it. I have added an additional ground cable and tried a variety of interference suppressor devices but to no avail.


The previous owner told me he did not have this issue which makes me suspect something I did caused the problem. For instance, I disabled the “Verkehrskurier” as it was causing the radio to malfunction. This required the radio to be taken out of the dashboard. I also took apart the electric Hirschmann antenna to clean its innards.


Is there anything I might have broken or disabled in the process that would have caused the radio to start emitting the interference?


Your advice is very much appreciated.

Tempur

 

[LostKiwi]

What type of noise? Is it a ticking noise or a whine? Is it RPM dependent?

 

[Tempur]

It's a low humming noise and RPM dependent. Any electrical switches, however, such as light, indicators, are also audible when used.

 

[LostKiwi]

A large capacitor across the live feed to earth and (if necessary) an inductor inline will almost certainly help. Also check the radio earth is good and that you aren't using the aerial to earth the radio.
I would suspect that the internal capacitors used to smooth the 12v supply may be a bit past it (the electrolyte dies out and the ability of the cap to smooth the incoming power diminishes).

 

[Tempur]

Will give that a try. Many thanks!