Radio works, CD works, No sound. MOST Bus?

[Kev85]

Hello!
I have a problem with my sound system
Audi A6 2.4 2005 year model
MMI Basic Plus
The radio / MMI / CD works but i get no sound from the speakers.

Sometimes when i start the MMI the screen lights up and then goes black and starts again.
I can play cds, i can see the seconds go up.

I have read a bit about the MOST Bus.
I disconnected the optical cable going to the amp
When i turn the ignition on i can see a red light from the optical cable but after a couple of seconds it flashes and then goes out.

Is the red light supposed to light up all the time?
I suspect that their might be a glitch in the optics so thats why it flashes and then goes out. What i have read so far is that the amplifier is the last unit in the ring?
So the next step i thought would be to disconnect CD changer and see how the optics behave when it is disconnected.

This fault has been for 2 years, the workshop hasnt been able to find the problem.
Kind regards
Kevin

[markaz]

Are you able to scan your car with VCDS?

[Kev85]

On the paper from the workshop it says, no communication with MMI
Faultcode on the optical bus
Coding not possible


Errors in MMI, Device: Interfacebox
0412, 00a HU not coded
0525, 04 Cluster ctrl
0824, 05a CompProt no co
082F, 00a ComProt active

[B5NUT]

Looks like Component Protection is active, you will need to get that removed by an Audi dealer, then you will get sound.

[Kev85]

It has been to the audi dealer, can it be that they cant erase it due to a faulty unit?

[B5NUT]

Then the only option is to get the part number off the current unit and have a look on ebay for a replacement. When you fit the replacement unit component protection will be active on the replacement so will require a trip to the dealer.