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Author Topic: Phone prewiring - where is U29?  (Read 1716 times)

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TheBoy

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Phone prewiring - where is U29?
« on: 21 October 2008, 18:49:12 »
I am trying to find a transformer, U29, which I think sits somewhere between prewiring plug and radio.

Looking at facelift wiring diags, looks like it may only be fitted to prefacelifts.
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Re: Phone prewiring - where is U29?
« Reply #1 on: 21 October 2008, 20:23:36 »
Quote
I am trying to find a transformer, U29, which I think sits somewhere between prewiring plug and radio.

Looking at facelift wiring diags, looks like it may only be fitted to prefacelifts.
Never found one on mine, not where they are on the pre facelift anyway, also checked up behind the glovebox so I tried it without and it puts the kit audio through fine.
TM is another story that I've yet to get to grips with though.
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VXL V6

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Re: Phone prewiring - where is U29?
« Reply #2 on: 21 October 2008, 20:44:51 »
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Re: Phone prewiring - where is U29?
« Reply #3 on: 21 October 2008, 20:49:05 »
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Possibly here:-

http://www.siocommunications.co.uk/Forum/index.php?topic=361.0
Saw that page myself but not on my FL.
« Last Edit: 21 October 2008, 20:49:23 by CaptainZok »
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Re: Phone prewiring - where is U29?
« Reply #4 on: 21 October 2008, 20:52:50 »
On the autoleads 06-109B (Nokia > prewiring adapter) there is an audio transformer built in to stop the bose going pop in a big way!  ;D

Not sure where or what the transformer is that TB is looking for.
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Re: Phone prewiring - where is U29?
« Reply #5 on: 21 October 2008, 20:57:03 »
Its an audio isolator/transformer I'm looking for

I shall check that location out...
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Kevin Wood

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Re: Phone prewiring - where is U29?
« Reply #6 on: 22 October 2008, 10:13:14 »
Could always feed 12v down from the telematics unit connector and see where the smoke appears. :-X

On the other hand, given that you've got a long cable run from the telematics unit to the head unit, the isolation the transformer provides might be beneficial in preventing a greound loop, so perhaps buffering the output of the telematics unit to drive it comfortably would be a better plan. Something like this: http://www.maplin.co.uk/Module.aspx?ModuleNo=2904 althoguh it's a shame it doesn't have a gain control...

Kevin
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Re: Phone prewiring - where is U29?
« Reply #7 on: 22 October 2008, 18:36:11 »
Quote
Could always feed 12v down from the telematics unit connector and see where the smoke appears. :-X

On the other hand, given that you've got a long cable run from the telematics unit to the head unit, the isolation the transformer provides might be beneficial in preventing a greound loop, so perhaps buffering the output of the telematics unit to drive it comfortably would be a better plan. Something like this: http://www.maplin.co.uk/Module.aspx?ModuleNo=2904 althoguh it's a shame it doesn't have a gain control...

Kevin
wiring straight to radio, bypassing the u29 gave decent audio with excpetion of bucket loads of cellular interference (not so bad that you couldn't here, but enough to be distracting).  Due to not using right cable I guess ;D
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Kevin Wood

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Re: Phone prewiring - where is U29?
« Reply #8 on: 22 October 2008, 23:53:52 »
Quote
Quote
Could always feed 12v down from the telematics unit connector and see where the smoke appears. :-X

On the other hand, given that you've got a long cable run from the telematics unit to the head unit, the isolation the transformer provides might be beneficial in preventing a greound loop, so perhaps buffering the output of the telematics unit to drive it comfortably would be a better plan. Something like this: http://www.maplin.co.uk/Module.aspx?ModuleNo=2904 althoguh it's a shame it doesn't have a gain control...

Kevin
wiring straight to radio, bypassing the u29 gave decent audio with excpetion of bucket loads of cellular interference (not so bad that you couldn't here, but enough to be distracting).  Due to not using right cable I guess ;D

.. or due to a ground loop?

Kevin
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Re: Phone prewiring - where is U29?
« Reply #9 on: 26 October 2008, 10:32:30 »
Quote
Quote
Quote
Could always feed 12v down from the telematics unit connector and see where the smoke appears. :-X

On the other hand, given that you've got a long cable run from the telematics unit to the head unit, the isolation the transformer provides might be beneficial in preventing a greound loop, so perhaps buffering the output of the telematics unit to drive it comfortably would be a better plan. Something like this: http://www.maplin.co.uk/Module.aspx?ModuleNo=2904 althoguh it's a shame it doesn't have a gain control...

Kevin
wiring straight to radio, bypassing the u29 gave decent audio with excpetion of bucket loads of cellular interference (not so bad that you couldn't here, but enough to be distracting).  Due to not using right cable I guess ;D

.. or due to a ground loop?

Kevin
Possibly  :-/ - though telematics gets its Gnd from CDC, which in turn gets it from somewhere behind dash...
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Kevin Wood

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Re: Phone prewiring - where is U29?
« Reply #10 on: 26 October 2008, 11:14:57 »
Quote
Possibly  Undecided - though telematics gets its Gnd from CDC, which in turn gets it from somewhere behind dash...

So the path to ground is quite long :-/. Current consumption of the telematics unit will be bursty as that's how GSM transmission works,  and it sinks this current into its' ground connection so you might find you end up with a 200Hz square wave superimposed on the ground at the telematics. Without a balanced audio signal back to the head unit that will end up on the audio. Depends on the input to the head unit, TBH. If it's referenced to ground at the head unit, it might be troublesome without the transformer. If it's 2 floating pins into the head unit, it might well be OK.

Kevin
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Re: Phone prewiring - where is U29?
« Reply #11 on: 26 October 2008, 11:18:29 »
The TM certainly doesn't like the impedence of the coils on isolator.  Would I get away simply putting a capacitor it? Or something more complex needed?
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