Hello Experts

I have just bought a 2002 S430. Standard equipment. No aftermarket audio, just the original BOSE multichannel amp in the trunk, connected via fibre optic cable to the head unit, phone, CD.

So far as I can tell, all the rear speakers seem to be working but, if I use the COMAND 2.5 system to adjust the fader so that it is 100% at the front, the only sound seems to come from the small speaker at the top of the dash in the centre of the car, i.e. nothing from the left or right front door speakers or the left or right tweeters mounted on the A pillars.

I disconnected the Bose amp and put a small voltage across various pairs of leads that come from the amp, going to the speakers.

I could get each of the speakers in turn (both rear doors, rear subwoofer, both front doors, both front tweeters) to crackle and pop so that seemed to indicate that there was no problem with the speaker wiring. I described the problem to Factory Car Stereo Repair in Florida and they agreed that it sounded like the amp so I sent it to them for repair. Unfortunately it seems like the amp is fine so I'm back to square one (minus $60 shipping costs there and back to find out!)

Does anyone have any ideas? Is there a pre-amp in the COMAND head unit that could be a problem? Thank you

Alastair

One has to wonder if the loaded amplifier works poorly. Testing on a bench doesnt really help.

__________________
www.benzmodz.com .... putting the Me into Mercedes.

Does your car have the digital BOSE system in it (I think it does by the sound of it) and thus the amp connected up with fibre optic connector as-well as the big connector with lots of wires ?

If so, there is nothing really to go wrong - the sound is sent down the fibre optic bus & thus it does sound like the amp is failing under load as Miro suggests

Richard

__________________
Of course i'll take it apart.

www.mercupgrades.com
http://www.comandonline.co.uk

All S-Class have BOSE even the MOST version. This is what is combined with the Seimens MOST head unit.

__________________
www.benzmodz.com .... putting the Me into Mercedes.

Thank you all for your replies. I would have replied sooner but forgot to turn on the setting that notifies me of postings.

Does anyone have any views on whether the Head unit has a pre-amp which could be the problem? The reason I suggest this is because if, as Factory Car Stereo Repair suggested, the amp has no problem then it must be to do with the input to the amp. If this is optical then it must be to do with the input to the fibre optic, which only leaves something in the Head unit. I also managed to get the Head unit into diagnostic mode and there are no error messages showing. A mystery. (Not sure if this can legitimately go in the "answers" section yet!)

Alastair

You have the digital bose amp. The sound is sent round the fibre optic ring digitally as part of the D2B protocol, i.e there is no discrete pre-amplifier -
- The COMAND tells the amp what volume etc to use for each channel, and sends the audio information for the channel as data) so effectively the pre-amp is in the digital bose amp itself.

But the control of the sound is done by the COMAND system of course - so if that is confused and telling the amp not to output any sound, it will not output any sound.

What I would do at this point is to
a) I'd do a 'reset to factory settings' on the COMAND and then pull the fuse for the COMAND, leave off for 10 mins, and power it back up again.
b) If that doesnt solve the issue, Id try and borrow an amp from somewhere else (or a COMAND unit from somewhere else)

- theres no other parts that you haven't tested that are involved in the sound output.

R

__________________
Of course i'll take it apart.

www.mercupgrades.com
http://www.comandonline.co.uk