Weird auto radio issue

[isw]

My son wanted to be able to play his iPod through his 2005 Mitsubishi's
audio system, and he'd heard that those FM gadgets didn't work well in
some cars, so we decided to add a normaling jack to the audio from the
CD player -- when the plug was out, the CD audio would go wherever it
goes, and when the plug was in, the ipod audio would go there instead.

Opened the radio up, and found a nice flat cable between the CD player
and the main board, with traces going to the connector in the player
labeled "LCH' "RCH", and "ACom". So that's where we cut traces and wired
in the normalng jack.

Problem is, it didn't work.

Whether the plug is in or not, the CD audio is all that comes through;
nothing from the iPod comes through -- that is, inserting the plug has
absolutely no effect. Buzzed everything out, and the wiring is just
fine. Looked at the LCH and RCH traces with the DVM; both appear to be
carrying audio when a CD is played, as expected. Actually removed the
added wiring, but left those two traces cut -- CD audio still came
through just fine.

On the main board, "ACom" goes to ground, and the *only* signals in that
cable passing through capacitors are "RCH" and "LCH"; the rest seem to
be resistively terminated, and using the DVM, they all show the sort of
AC voltage that you'd expect from a digital bit stream -- no other
traces in the cable appear to be carrying analog audio.

So what's going on here? Is the radio actually getting a digital stream
from the CD player? Because it's pretty clear that those two "audio"
streams aren't doing very much.

Isaac

 

[Franc Zabkar]

On Fri, 03 Apr 2009 20:52:04 -0700, isw <isw@witzend.com> put finger
to keyboard and composed:

My son wanted to be able to play his iPod through his 2005 Mitsubishi's
audio system, and he'd heard that those FM gadgets didn't work well in
some cars, so we decided to add a normaling jack to the audio from the
CD player -- when the plug was out, the CD audio would go wherever it
goes, and when the plug was in, the ipod audio would go there instead.

Opened the radio up, and found a nice flat cable between the CD player
and the main board, with traces going to the connector in the player
labeled "LCH' "RCH", and "ACom". So that's where we cut traces and wired
in the normalng jack.

Problem is, it didn't work.

Whether the plug is in or not, the CD audio is all that comes through;
nothing from the iPod comes through -- that is, inserting the plug has
absolutely no effect. Buzzed everything out, and the wiring is just
fine. Looked at the LCH and RCH traces with the DVM; both appear to be
carrying audio when a CD is played, as expected. Actually removed the
added wiring, but left those two traces cut -- CD audio still came
through just fine.

On the main board, "ACom" goes to ground, and the *only* signals in that
cable passing through capacitors are "RCH" and "LCH"; the rest seem to
be resistively terminated, and using the DVM, they all show the sort of
AC voltage that you'd expect from a digital bit stream -- no other
traces in the cable appear to be carrying analog audio.

So what's going on here? Is the radio actually getting a digital stream
from the CD player? Because it's pretty clear that those two "audio"
streams aren't doing very much.

Isaac

Do you have a test CD that produces a sinusoidal output? You can also
turn off L and R channels to see if one side goes quiet.


- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[isw]

In article <o6skt4942422lf5vii62ihl91a1q0d4idj@4ax.com>,
Franc Zabkar <fzabkar@iinternode.on.net> wrote:

On Fri, 03 Apr 2009 20:52:04 -0700, isw <isw@witzend.com> put finger
to keyboard and composed:

My son wanted to be able to play his iPod through his 2005 Mitsubishi's
audio system, and he'd heard that those FM gadgets didn't work well in
some cars, so we decided to add a normaling jack to the audio from the
CD player -- when the plug was out, the CD audio would go wherever it
goes, and when the plug was in, the ipod audio would go there instead.

Opened the radio up, and found a nice flat cable between the CD player
and the main board, with traces going to the connector in the player
labeled "LCH' "RCH", and "ACom". So that's where we cut traces and wired
in the normalng jack.

Problem is, it didn't work.

Whether the plug is in or not, the CD audio is all that comes through;
nothing from the iPod comes through -- that is, inserting the plug has
absolutely no effect. Buzzed everything out, and the wiring is just
fine. Looked at the LCH and RCH traces with the DVM; both appear to be
carrying audio when a CD is played, as expected. Actually removed the
added wiring, but left those two traces cut -- CD audio still came
through just fine.

On the main board, "ACom" goes to ground, and the *only* signals in that
cable passing through capacitors are "RCH" and "LCH"; the rest seem to
be resistively terminated, and using the DVM, they all show the sort of
AC voltage that you'd expect from a digital bit stream -- no other
traces in the cable appear to be carrying analog audio.

So what's going on here? Is the radio actually getting a digital stream
from the CD player? Because it's pretty clear that those two "audio"
streams aren't doing very much.

Isaac

Do you have a test CD that produces a sinusoidal output? You can also
turn off L and R channels to see if one side goes quiet.

I have a test CD, and both channels come through, unimpaired, even when
the LCH and RCH connections are broken (and tested with an ohmmeter).

Isaac

 

[Franc Zabkar]

On Mon, 06 Apr 2009 20:54:43 -0700, isw <isw@witzend.com> put finger
to keyboard and composed:

In article <o6skt4942422lf5vii62ihl91a1q0d4idj@4ax.com>,
Franc Zabkar <fzabkar@iinternode.on.net> wrote:

On Fri, 03 Apr 2009 20:52:04 -0700, isw <isw@witzend.com> put finger
to keyboard and composed:

On the main board, "ACom" goes to ground, and the *only* signals in that
cable passing through capacitors are "RCH" and "LCH"; the rest seem to
be resistively terminated, and using the DVM, they all show the sort of
AC voltage that you'd expect from a digital bit stream -- no other
traces in the cable appear to be carrying analog audio.

So what's going on here? Is the radio actually getting a digital stream
from the CD player? Because it's pretty clear that those two "audio"
streams aren't doing very much.

Isaac

Do you have a test CD that produces a sinusoidal output? You can also
turn off L and R channels to see if one side goes quiet.

I have a test CD, and both channels come through, unimpaired, even when
the LCH and RCH connections are broken (and tested with an ohmmeter).

Isaac

You could listen for analogue audio with a piezo earphone coupled via
a capacitor and possibly a series resistor.

A test CD that enables you to turn off L or R channels would confirm
which was which.

If you could get access to the component side of each PCB, then
identifying each chip may help you determine its function. However, I
realise this may be impossible without removing the deck assemblies.

Does your car audio unit allow you to connect a hands free mobile
phone? If so, then that may provide you with an analogue input.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.