Weird auto radio issue

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

Reply to
isw
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On Fri, 03 Apr 2009 20:52:04 -0700, isw put finger to keyboard and composed:

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

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Reply to
Franc Zabkar

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

Reply to
isw

On Mon, 06 Apr 2009 20:54:43 -0700, isw put finger to keyboard and composed:

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

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Reply to
Franc Zabkar

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