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Hewi
Member Since: 12 May 2022
Location: Sorunda
Posts: 2
  
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Hi all!
I have no sounds in my Disco 3 but the change of channels or source
is shown in the head (radio) unit, at least that works.
Fault code from my GAP tool is U2003-31 (2A):
”Fiber communication bus – Frequency modulation/pulse
width modulation failure – no signal”
I have visually checked all cables between head unit and the amplifier.
(Yes I had to removed all relevant dash and central console trims)
And of course checked even fuses and voltage.
The fiber optical cable is connected only between those two units (in this version of LR3).
Have also tested to make a hard reset as shown in a you tube clip.
Since I don´t know from where the GAP tool pick up information, my conclusion is
then that it must be fault In either the head unit, amplifier or the opitical fibre cable.
So, my question is how to find out which unit it is.
Is there any good ideas out there?
Regards Henrik Disco 3 2008
Member of Sweden Land Rover Club, SLRK
Kabe RV
Fiat Panda 4x4
BMW G650Gs
BMW G650GS
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 11th Jul 2022 10:23 am |
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Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10373
 
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Well the optical cable can be tested with a torch to see if light is appearing at the other end.
Amplifiers fail quite a lot. See if there is a red light on the amp fibre connector shortly after you turn the head unit on.
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| 11th Jul 2022 12:34 pm |
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Hewi
Member Since: 12 May 2022
Location: Sorunda
Posts: 2
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Thanks!
Tested with a Torch and it lights through both fibers. Ok it seems to be ok but without knowing
if there are any loses in fiber cable, but probably not.
Yes, it lights red in one of the fiber when reconnected from the amplifier. I´m sorry but I don´t get what
conclusion could be of that?
(My Disco is an 2008, I took it over 2012)
Regards
Henrik Disco 3 2008
Member of Sweden Land Rover Club, SLRK
Kabe RV
Fiat Panda 4x4
BMW G650Gs
BMW G650GS
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| 12th Jul 2022 9:10 am |
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kajtzu
Member Since: 11 Aug 2017
Location: Helsinki
Posts: 6577
 
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It means at least the amplifier has power and isn’t completely dead. The transmitting light diode seems to work as you see the red wavelength (centerline is around 650 nm). This happens in every node on the ring (bus). One fiber is always RX (receive) to each device and the other is TX (transmit) from each device (and connected to RX on the next one). You can think of the ring as unidirectional in that sense. A frame from one node to the previous one must traverse the whole ring.
TBH I’m not sure how to pinpoint the root cause but as the bus is synchronous it does require a timing source. My understanding is that the source or bus master is the IHU, which is part of the stereo unit. It supplies the bus with transmission frames. The rest of the devices (amplifier, phone module, etc.) are slaves on the bus and expect to receive a synchronous signals at all times. If the IHU is faulty the bus won’t have something generating frames and thus there won’t be traffic on it.
Edit: from “experience” I can say that an optical fiber can be very bent, in crap shape, connector or receptacle spit on or dusty and it’ll still work to a very large degree even at high data rates. The D3 has a rather slow bus so this is most likely not a problem unless the fiber has been bent somewhere 90 degrees or gotten trashed between a door  
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| 12th Jul 2022 8:58 pm |
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Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10373
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Yeap, exactly 
Basically it a bit of a guess, whether to get a replacement amp, and then if it doesn't sort it, get a headunit.
or you could decided for the cost of those 2 items, a new, fancy replacement headunit with mp3 and BT would be cheaper.
Note (if you go aftermarket) the wiring looms to run from the head unit, to the connector by the amp can be very expensive ~£250
But its just wires, so sometimes you can get cheaper
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| 12th Jul 2022 10:15 pm |
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G15MTS
Member Since: 28 Oct 2019
Location: Stockholm
Posts: 118
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Had the exact same issue a few years back. It was a fault within the amp, the optics etc were all looking ok but I still chose to swap out the amp after hours and hours of trying everything else. I bought one second hand from a scrap yard and it solved it.
Incidentally my original amp looked brand new (low milage car with back seats barely used) the one I replaced it with looked terrible but worked....
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| 13th Jul 2022 9:55 am |
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lynalldiscovery
Member Since: 22 Dec 2009
Location: Maidstone
Posts: 7274
 
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I had the same, and it was one fo the two boxes behind drivers side boot panel, think it was phone box that went tits up, i just butted the ends of the fibre optic together and taped them up so the radio worked.
Then got a 2nd hand box, and that was no good, so just swapped the cabling about to remove the phone box from the circuit.
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| 14th Jul 2022 7:30 am |
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kajtzu
Member Since: 11 Aug 2017
Location: Helsinki
Posts: 6577
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OP said he only has the stereo and amp, nothing else on the ring.
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| 14th Jul 2022 4:39 pm |
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Barnetman
Member Since: 26 Mar 2020
Location: BARNET
Posts: 84
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I've had the same problem. Did all the usual checks bought a new head unit worked for a while, did the hard reset worked for a bit longer. 
It now has the same problem so I've decided to live with it some times it works some times it doesn't, it's a land rover after all..
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| 15th Jul 2022 11:44 am |
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