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I did call Comandonline, as expected they won't help without paying up £120 first. I really don't want to pay £120 just to find out what MOST component position 3 is. They also don't repair anything. They will only replace units. So if the AMP is busted they said you'll have to buy a new one from MB for £1500.
I know there have been various threads for various models on various MB forums in the states and here in UK, however they are all under different circumstances and in different models leading up to the problem I have with my W221 S500.

Help is appreciated from all but I'm hoping to hear from facelift S Class owners with the Harman/Kardon sound system who have experienced the same problem under similar circumstances.

Problem started after coming back from a 3 week holiday on 30th of March. Came back to the car completely dead. Jump started the car next day, went for a motorway cruise and noticed DAB radio said "Device Unavailable", tried switching to FM or AM but still same message. Tried Music Register (internal 8GB hard drive), no error message and could select tracks but the timer just stayed on 00:00 and nothing happened. Then tried selecting AUX played music on phone but no sound. Then about 20 minutes in to my cruise I left the motorway to turn back from a junction. At the traffic lights (forgetting the purpose of my cruise) I thought I'd switch the car off and on to maybe bring sound back again. Switched off went to start engine and the starter motor struggled and gave up completely on 2nd attempt and also refreshed my memory as to why I went on this random cruise. Called the cavalry (my brother) and jump started the car again and to my relief everything was working again. However noticed sound kept cutting out every few seconds, thought it was just bad phone signal as I was playing music via AUX on youtube. Switched to "Music Register" and the same problem sound kept cutting out. Every time the sound did cut out it faded back on as if coming back on from mute (not sure if this is a feature in all MB models, but is in the S Class).

Got home after my 20 + 20 minute cruise + 15 minutes battery dead period in between. Switched engine off, (not to confident it would start again) and as expected battery didn't have enough juice to start engine again. Next day went for another cruise, 50 minutes this time, Sound still cutting out, extremely annoying so just switched audio off. Got home same story, still not enough charge to restart engine. Then forked out £90 on a Noco Genius smart battery charger. Charger came the next day, left the battery hooked up overnight and next morning charger was showing 100% charged. Hit the start button and the engine effortlessly growled in to action.

Now the real problem started. Car switched on with COMAND set on DAB radio, now showing initial message of "Device Unavailable", However it was different this time. Went to select FM/AM but the menu wouldn't pop up to show all 3 option of DAB, FM and AM. Scrolled to Music Register still same problem. Went to select AUX, option is greyed out. Tried to select Memory Card, Music interface, CD, USB, TV, DVD but all showing Device Unavailable or just doing nothing. Tried connecting phone to bluetooth, did connect and could make and receive calls but no sound through car speakers. Then tried Nav, input a destination, route came up ok but again no audiable instructions from Nav.
Started looking up on forums came across threads where owners experienced similar problems but most seemed to resolve by just disconnecting battery for 30 minutes or going to a STEALERSHIP under warranty and they fix with software updates or replacing the AMP or COMAND unit. A few threads in the states fixed by disconnecting Sirius units, no idea what that is but I’m guessing that's the DAB signal receiver unit, but in the states they call it SAT radio. But those issues were mostly with ML or R class Mercedes and I think just issue with DAB saying Device Unavailable not everything.

I’ve tried all the above apart from going to a stealership. Still no fix. My local specialist has the STAR diagnostic but it had been sent away for updates. I grew impatient and removed the boot lining unplugged DAB unit and the HARMAN/KARDON AMP for 30 minutes, noticed the fan on the AMP spun for a split second when plugging back in so was a bit optimistic. However Still no fix. Reading a few more threads I learned the AMP could be busted and owners experienced this after jump starting or charging a dead battery, one thread even had the issue of Device Unavailable after MB themselves replaced the dead battery. So now I’m suspecting a fried AMP So completely removed the AMP and opened it up. Found black sooty residue directly below where the fan sits on the cover. I sent the pictures to my colleague who is a qualified avionics engineer and knowns his stuff. Straight away he thought a discharge has occurred, I mentioned it was below the fan. His theory…… fan blows air in, instead of out, so dust has accumulated inside AMP and caused a short, thus damaging components in the AMP. He recommended attempting to clean with electrical contact cleaner. So I vacuumed up the soot using a very soft brush and sprayed the area very carefully with the contact cleaner, making sure it didn’t pool up and done it under the sun to make sure it evaporates quicker. Reinstalled AMP, sadly still no fix. (Sorry could not attach pictures of AMP internals, error come's up saying file to large on forum)

I am now waiting for my local specialist to get his STAR diagnostic back and have starting calling up companies specialising in repairing car electronics some even having mention of Mercedes / Harman/Kardon AMPs on there websites as it seems to be a common issue with MB.

In the mean time any help or solutions would be greatly appreciated from owners who have experienced similar issues under the above circumstances and if anyone has had to go down the route of repairing the AMP who have they used or would recommend using, as I don’t want to end up paying someone hundreds of pounds repairing the AMP and still end up buying a new one or worse end up at the stealership, which might happen any way as I think the AMP's have to be programmed after repair. Which unfortunately can only be done at MB, unless anyone knows something I don't.
Hi Sir,
Did you find the fix for the this, I have S500 2010 and facing exactly the same issues "device unavailable".

Thank you.
I had this issue and sent the amp away for repair (£400).
The biggest killer of these amps is that the cooling air is pulled in from outside, behind the bumper near the exhaust...

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