Hi, I recently bought a Clk 270 CDI with Audio 20 and Harman Kardon, but I have a problem, I can only turn up the volumen from 0 to 20% and no more, with the steering wheel buttons and the radio ones. I can select surround on the radio, I reset the radio, check fader and everything on it and nothing.

 

I just picked my CLK350 from the garage after changing discs and pads and noticed the same thing on my car. I too have the Harman Kardon Logic 7 system installed. Just wondering if I leave it over night it will resolve itself.
did you get it sorted in the end?

 

The amp was broken.