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checking / removing sub in Avant '98

Discussion in 'A4/S4 forum(B5 Chassis)' started by TeKnodriver, Jul 20, 2011.

  1. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    Hi,
    I'm trying to get a better look or remove the sub in a '98 Avant...

    Haynes manual says remove rear seat base and backs - is this necessary?

    would be good to get the sub out to make room for a larger amp for external sub

    [bits I have from last car]

    Thanks!

    (fitted new HU using the wiring adaptor that was already there -
    I get 12v feed and 5 to 6v on the signal leads coming out of the adaptor,
    but rear speakers and sub do not function.
    the HU I removed had the rears and sub working)
    #1
  2. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    I suspect the new head unit isnt sending the "remote" signal down the correct wire to power the sub/amp on.

    To remove the sub you need to take the side panel off, which requries at the very least you lower the back seat, and remove the side bolster bit.
    #2
  3. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    Cheers for info - I did think taking all the seat out was a bit OTT...
    got a coolant leak to sort first (just O ring where the sensors meet the block)

    I get 12v feed on the blue wire - constant while HU is on
    and 5 to 6v on the signal leads coming out of the adaptor,
    fitted new HU using the wiring adaptor that was already there [looks just loike Autoleads PC 9401]
    but rear speakers and sub do not function.
    the HU I removed had the rears and sub working though, so a bit confusing.
    #3
  4. S4_dan
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    S4_dan Fire up the Quattro!

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    I have just removed my Avant amp/sub. I only lowered smaller rear seat back and pulled the boot trim away partially after undoing couple of screws. That gave me more than enough access without removing therear seat bolt thingy that catches the seat back and locks to it.

    Check that the blue wire is connecting nicely in the terminal block and its in the right hole in the block. Alternatively, cut the wire that feeds the amps and join directly to the blue wire?

    Dan
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  5. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    checked the connector at the sub and found there's a healthy 12v geting there and the signal level is around 5v
    by my assumptions this would mean the amp indside is fried?..

    I think it's going in the bin to make room for louder things ;)
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  6. S4_dan
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    S4_dan Fire up the Quattro!

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    signal leads = audio in leads?
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  7. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    not sure...
    there's one multiblock connector thinngy i can see,
    therefore i'm assuming it acts as the 12v in / line in / rear speakers out connection as there are a lot of wires there, no separate in/out

    speaker output from HU through the adaptor is around 5 -6v
    pretty sure the audio's getting there
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  8. S4_dan
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    S4_dan Fire up the Quattro!

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  9. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    There is a permenant (well switched) 12v feed to the sub, plus a remote trigger from the head unit.

    The permenant feed is quite large, whereas the trigger is much smaller.

    ahha, if you look at the pic that s4dan posted above, in the Line-out block you can see the pin with a switch symbol and a +. Thats the switched live that needs to be making its way to the sub amp to turn it on.
    Last edited: Jul 22, 2011
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  10. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    thanks for pointing me in the right direction on Audi's pedantic wiring system ;)

    i'm a little confused over the permanent 12v and switched 12v feeds to the rear connector...
    any furthr clarification possible?
    cheers
    #10
  11. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    The big red and blue wire is live all the time (at least when the ignition is on anyway)

    The remote wire is smaller and a different color (white perhaps) it is only live when the stereo is on. Its this wire that needs to be connected to the blue wire on the head unit to power up the amplifier.
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  12. S4_dan
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    S4_dan Fire up the Quattro!

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    Yes it is a small thin white wire from the yellow connecter at HU end that is a switched 12v for the amp! But in Audi's wise wisdom, there is also a thin white wire on the same block which is speaker ground (common)!! Don't mix the two up! lol
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  13. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    Got it working!
    but by a pretty random method...
    bridging the red/blue wire [that should be ign/acc or +12v constant]
    with the white remote wire,
    ie. the top 2 wires in photo below

    [​IMG]

    [just borrowing your photo S4_Dan] thanks!

    This at least confirms the sub/amp has not been fried and is working,
    however, I can't think of a permanent solution as I can't find where the +12v red/blue wire feeds from.

    still, if it sound as bad as others have noted I'll be swapping it for 500w of proper bass!
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  14. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    is the red/blue wire dead?
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  15. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    absolutely no voltage on the red/blue -
    any idea where it feeds from?
    it doesn't seem to come out of the back of the HU
    #15
  16. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    You need to work out if you are feeding 12v from the perm live to the trigger or from the trigger to the perm live. Invest in a 12v testing screwdriver (£2.99 from maplins or halfords). Chances are you are feeding the perm live to the trigger which means you need to check the wiring at the HU. I doubt even Audi's feeble excuse for a subwoofer would be able to power itself off the miniscule current available on the remote trigger wire, it would shutdown the HU immediately as it is purely a trigger and cannot support any load current beyond a few milliamps
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  17. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    sounds about right...
    I did think this would not be a proper solution!
    by bridging them it's now all feeding off the 12v remote trigger

    I can't find where the red/blue wire comes from - is it straight from the fusebox?
    #17
  18. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    I'd disconnect that immediately, as that 12v trigger isnt designed to deliver much more than a few 100 miliamps, and the amp will draw many times this.

    If that red/blue is dead, its probably a fuse.
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  19. TeKnodriver
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    TeKnodriver Biodiesel Purrrr

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    anyone know where this red/blue wire feeds from?
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  20. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Its shared with the supply to the radio itself, fuse S237 (probably 37 in the fusebox) should be 20A

    Its also a permenant live.
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