Understanding the factory CD and boot amp

[foxdie]

Hi folks, this thread is intended to piece together information from fellow club members, other enthusiast forums and personal research. It is a work in progress and will be amended as time goes on.

Part 1
As some of you are aware, a small percentage of 8G VR-4's left the factory with an upgraded in-car entertainment system which comprised of a 10-disc CD changer, 4.1 amplifier and an 8" subwoofer, all of which located in the boot. @phosty took some excellent photos here.

For those (un)lucky enough to have come into ownership of these cars, upgrading the head unit to an aftermarket model is fruitless without either installing an aftermarket 3ch/4ch amplifier or worse, running cables to all the individual speakers.

The reason for this is because (on these particular) variants of the VR-4, the speaker wires do not terminate behind the centre console like in every car, they terminate in the boot under the spare wheel cover. You can buy a Mitsubishi-to-ISO loom and it will power up the radio, however you will have no sound. I found this out the hard way recently when I tried to upgrade to a Kenwood single DIN stereo.

In these particular variants, the audio is sent separately to the amp in the boot by a 13-pin DIN connector like the following (rightmost connector);

Mitsubishi Legnum Head Unit connectors.jpg

After a bit of playing about, it became clear that audio from these factory upgraded head units was being sent to the amp in the back via a 13-pin DIN cable, so out came the multimeter and I started to try and find a way to replace this unit. This is what I found;

=== This information is incomplete!! ===

1. Right Channel Audio
2. N/C
3. Left Channel Audio
4. Audio Ground
5. N/C
6. N/C
7. Remote amp (+12V when radio is on, GND when not)
8. N/C
9. +5V (data signal)
10. +5V (data signal)
11. Gnd (possibly for above)
12. N/C
13. +5V (data signal)

=== This information is incomplete!! ===

So the first thing I thought of was "Can I feed audio into the amp if I power it up manually?", the answer was sadly no, even though I could hear the speakers quietly clicking when I turned the amp on and off with Pin 7, nothing came out. That's when I started to think about the serial lines.

This is further reinforced by the fact that the audio coming from Pins 1, 3 & 4 was unaffected by the volume control / tone control / fader / balance. It was a constant line level output whilst the head unit was on (specifically the radio input but I imagine it would be the same for the tape).