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Discussion Starter · #1 ·
Just got a used 2007 SLK 280.

Got the CDC in my glove compartment, but no lights illuminate when I press any of the buttons. When I push the CDC button on the audio 20 display, I get a "NO CDC" message.

Any ideas?

(Other than ripping the thing out which I will probably do later)

Thanks
 

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Discussion Starter · #3 ·
I was wondering about that.

Unless the CDC needs to be initialized from the HU before anything works, I would guess it is missing power.

Thanks for the link. I read it and need the link working since there's a Sirius radio, though that isn't showing up either. (Post http://www.slkworld.com/slk-r171-general-discussion/313714-sirius-question.html). To help me diagnose, does anyone know:

1. Does the CDC need to be set up from the HU before it's operational and the buttons work? In other words, will a broken MOST link make the CDC appear dead / unpowered?
2. If the CDC fuse is blown, would that take down the MOST link?
3. If the Sirius fuse is blown, would that take down the MOST link?

Found a fuse diagram here but still need to dig to get there.

Didn't fund much here on diagnosing MOST problems; time for more googling!

Thanks for any help.
 

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I was wondering about that.

Unless the CDC needs to be initialized from the HU before anything works, I would guess it is missing power.

Thanks for the link. I read it and need the link working since there's a Sirius radio, though that isn't showing up either. (Post http://www.slkworld.com/slk-r171-general-discussion/313714-sirius-question.html). To help me diagnose, does anyone know:

1. Does the CDC need to be set up from the HU before it's operational and the buttons work? In other words, will a broken MOST link make the CDC appear dead / unpowered?
2. If the CDC fuse is blown, would that take down the MOST link?
3. If the Sirius fuse is blown, would that take down the MOST link?

Found a fuse diagram here but still need to dig to get there.

Didn't fund much here on diagnosing MOST problems; time for more googling!

Thanks for any help.
fuse locations here:

http://www.slkworld.com/slk-r171-class-diy/187817-r171-fuse-relay-locations-pics-descriptions.html
 

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1. Not sure, but I tend to think that it will power up (that is to say if the unit is not broken) even with an interrupted MOST ring.
The ring is controlled by the AGW that's built in your Audio 20. This AGW wakes up all components on the ring with a separate electrical signal (so not through the ring) on a separate wake-up line.
2.Yes
3.Yes

In short, any device on the ring that will not power up will take down the ring. Easy fix is to disconnect that device and close the ring with an optical loop plug.

More info on MOST (how it works and how to diagnose) here and here .
 

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Discussion Starter · #6 ·
In short, any device on the ring that will not power up will take down the ring. Easy fix is to disconnect that device and close the ring with an optical loop plug.
Well that was fun! Found those pix and took my trunk carpet apart. Buzzed out all the fuses and they're good. For good measure, I filed down he contacts to clean metal.

No difference.

I also pulled out the Sirius connector and put it back - maybe bad power connection. No dice.

Is the light on the optical cable visible? Looking at it with the car powered, I didn't see anything. ** Scratch that question - the link says 650 nm which is visible red ** I am alone, so cannot look at the fiber while the ignition is turned on.

The main audio unit works fine, so hopefully the built-in AGW is getting power and working.

Guess that means pulling the CDC out is the next step. Especially if it should power on even without a ring. (I have no lights of anything on the CDC.)

Sounds like patching the Sirius and/or CDC with an optical loop could help identify the faulty unit. I see lots of discussions on the site about where to get one.

It would also be helpful to know how the optical loop runs through the car. Looking at the drawing on slide 12 of the Audio & Communications training presentation, it's not stated whether the ring goes clockwise or counter clockwise. It's also not clear what the little black rectangles represent - a coupler? If so, that's another failure point.

Have to say thanks to everyone for helping out here. The background info on MOST is, well, most helpful.
 

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Discussion Starter · #7 ·
Guess that means pulling the CDC out is the next step. Especially if it should power on even without a ring. (I have no lights of anything on the CDC.)
Well, thanks to the great info on this site, the CDC is out and I have enough room in my glove compartment for the usual papers.

As for troubleshooting the MOST ring, I stared at the optical connector while turning the key. Nothing. When I pushed the CDC button on my audio unit, nothing. (Still "NO CDC" which I expected, but was hoping to see some light flashing.) SO... can you really see light on the optical connector? Is that a useful troubleshooting technique?

I'll head to the dealer later to pick up an optical coupler and try to bypass the CDC to see if I can get the Sirius unit to work. ($11 plus tax for a piece of plastic!)

I also noticed that the connectors were labeled 1(in)/4(out on the CDC and 13(in)/16(out) on the Sirius unit.

Does anyone have a diagram that shows the routing of the fiber cables through the vehicle? Ideally with the cable numbers? If the bypass doesn't work, I'll need that to check all the couplings. The Audio & Communications PDF file doesn't have that detail. The attached drawing (from slide 12) would suggest that the HU to CDC fiber runs behind the passenger seat rather than directly from the Audio 20 to the CDC.

I guess this is a result of trying to run identical cabling for Audio 20 and COMAND HUs.
 

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Look at page 13 and 14 in this document.

It is for installation of a cellphone unit but shows on page 14 the sequence of the different devices on the ring. According to the text on page 13 this sequence is mandatory, so I would expect it is valid for your SLK. Diagram shows Sirius unit before the CDC so if you don't see light at the CDC possible the problem is with the Sirius unit. But as you can see it is for Comand that has a seperate HU and AGW, so I'm not sure but who knows?
Anyway interseting, let us now if and how you were able to solve it.
Good luck!
 

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Well, thanks to the great info on this site, the CDC is out and I have enough room in my glove compartment for the usual papers.

As for troubleshooting the MOST ring, I stared at the optical connector while turning the key. Nothing. When I pushed the CDC button on my audio unit, nothing. (Still "NO CDC" which I expected, but was hoping to see some light flashing.) SO... can you really see light on the optical connector? Is that a useful troubleshooting technique?

I'll head to the dealer later to pick up an optical coupler and try to bypass the CDC to see if I can get the Sirius unit to work. ($11 plus tax for a piece of plastic!)

I also noticed that the connectors were labeled 1(in)/4(out on the CDC and 13(in)/16(out) on the Sirius unit.

Does anyone have a diagram that shows the routing of the fiber cables through the vehicle? Ideally with the cable numbers? If the bypass doesn't work, I'll need that to check all the couplings. The Audio & Communications PDF file doesn't have that detail. The attached drawing (from slide 12) would suggest that the HU to CDC fiber runs behind the passenger seat rather than directly from the Audio 20 to the CDC.

I guess this is a result of trying to run identical cabling for Audio 20 and COMAND HUs.
You should be able to see the Red light. For testing purposes you can simply put the two ends together that came from the CDC (have to take the cables out of the holder). Some people have used something like an old Bic ball point pen housing to slide the two fiber cables into and hold them end to end. I used a small section of vinyl tubing that was just the right inside diameter to hold the cables snugly.

You may want to have your car hooked up to MB DAS which is the diagnostic system. It will tell you exactly where the issue is with the ring. All dealers and better independent MB service facilities should have the equipment. Some of our members also have it so you may want to see if one is near you and willing to help you out.
 

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Discussion Starter · #10 ·
... You may want to have your car hooked up to MB DAS ...
Had to replace the engine mounts, so used the opportunity to have the shop look at my MOST ring.

On the Star system, no devices were configured for the ring. No idea when this happened since the previous owner swore that the CDC and Sirius were working when he traded it in and the Lincoln dealer is unlikely to own the required system.

Nonetheless, the mechanic added just the Sirius satellite radio to the ring and reset the ring. After I activated it with Sirius - voila - music!

Have to guess that the Audio 20 HU doesn't bother to activate the ring if no devices are configured on it. Never saw the 4 red flashes before. I'm not going to take it apart, but I would bet there're there now.

Have to thank everyone for their help on this forum.
 

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Had to replace the engine mounts, so used the opportunity to have the shop look at my MOST ring.

On the Star system, no devices were configured for the ring. No idea when this happened since the previous owner swore that the CDC and Sirius were working when he traded it in and the Lincoln dealer is unlikely to own the required system.

Nonetheless, the mechanic added just the Sirius satellite radio to the ring and reset the ring. After I activated it with Sirius - voila - music!

Have to guess that the Audio 20 HU doesn't bother to activate the ring if no devices are configured on it. Never saw the 4 red flashes before. I'm not going to take it apart, but I would bet there're there now.

Have to thank everyone for their help on this forum.
Glad to hear you got it working. Thanks for updating the thread. DAS can make short work out of sorting through a problem. If at all possible it should be the starting point of trouble shooting.
 
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