Ok, here is the story, i couldnt find many of the pictures, so i ll try to write what i remember by heart, so gimme a break
I just hope i dont remember anything wrong
What you will need:
1) A blaupunkt removal key ( to remove the hu)
2) A flat headed screw driver
3) A T8 torx tool ( those star shaped little screw drivers used at mobile phones repairs)
4) Two golden plated RCA females
5) 1m of thin and flexible coaxial cable, proper for audio applications
6) a BC638 pnp tranzistor
7) a 2.2KΩ resistor
8) a 1N4001 diode
9) a double switching 12V relay
10) a soldering iron
The subject is this: We ll get signal for the RCA output from the final stage amplifier's input.
We also have to get out a wire which will turn on and off the amplifier. Sounds simple, but if you
do it like that, you ll get a HUGE NOISE at power-on and power-off at your speakers (pulse signal
generated at the preamp stage due to various reasons.) This pulse noise isnt audible through the build
in amplifier because the amplifier is at mute mode for a second when you turn on the hu. All we have
to do is to put a relay, at the rca singal. The relay will be turned on at power on, and off at power off
instantly. At the power-on, if your amp has a soft-start feature ( most amps have it) there wouldn't be
any problem, but at power-off the amp stays active for some seconds until its power supply capacitors
discharge, so the pulse noise will be heard. So we put the relay to cut off the signal imediately.
The pain in the arse was that... there wasnt any voltage at the hu's board that gets low right after
the power off. All circuit has 12V voltage for 20minutes after the power off !!! Then with a command
from the can bus, the power supply is off. The display was the only thing that really gets its voltage
low, so I had to bias a tranzistor from the display's led and control the relay and the REMOTE output
for the amp, through it.
What you have to do:
Make sure the head unit is switched to radio mode before you turn it off.
1) Open the head unit's cover using a flat headed screw driver. No screws need to be undone there.
Removing the cover, voids warranty. I know you know, but I have to say it
2) You have to remove the cd-player mechanism. There are 4 torx screws that hold it. There is a
flat cable undereath that has to be unpluged. Before you remove it, notice around how much free
space you ve got, to place the small circuit and the realay. HAve the relay seperately than the rest
circuit (shown in the 1st attached image), to have space flexibility.
3) Remove the silver part of the fascia by unscrewing the 5 trorx screws that hold it. You have to
locate a led ( from the display's illumination ) and solder a thin wire to the negative pole. The
negative pole is upwards, and the led can be seen in the 3rd attached pic. This will be POINT A
4) Restore the fascia.
5) There is one voltage regulator at each side of the head unit ( an upright IC with 3 pins) One of the
pins is 12V input, one is ground, and the other one is the output (9 volts if i remember). You have to
locate the 12V pin ( give power supply to the head unit and turn it on, use a multimeter to measure it
- it doesnt matter if the cd-tray mechanism is removed) Solder a wire on this pin, this will be POINT B
of the circuit
6) Locate the output IC on the left of the hu (you cant miss it
). Since you have a 147TI, I suppose
its the latest version of the 937 head unit, having the TA8276
4-channel amplifier IC. You will
acquire your RCA signal from the IC's input. Pins 11, 13, 15 are LEFT IN, GROUND, RIGHT IN.
are two of the four inputs ( the front speaker ones). Dont even think about making 4 RCA outputs,
the REAR channels inputs are located at the rear pins of the IC so you ll find a hard time reaching them..
If you ll need to feed a 4-channel amp, you ll just use a Y RCA spitter cable. Solder the coaxial cable
to those pins. The other edge of your cable, will go at the relay's contacts. Glue the relay at the
rear surface of the hu. The cable will have to pass underneath the cd-mechanism, so it has to be thin
7) You have to build a small circuit with these elemets: 2K2 resistor, 1 tranzistor, 1 diode. Look at
the attached image for details. When you finish, seal it with professional electrical tape
(i used cloth-type tape which lasts longer at high temperatures) and place it at the TA8276 side, near the front fascia.
8) Restore the cd-tray mechanism. Plug the flat cable and do the torx screws. Make sure no cable interferes with its operation
9) At the rear surface of the hu, there are holes you can use to pass out the RCA cable, and the remote cable
Use cable ties and/or heat glue to stabilize the cables at the holes. They must be firm, they shouldnt
move at all inside the hu, or they can mess with the cd mechanism.
10) Do a final check, and give 12V supply. If everything went well, you should hear the click sound of the relay on power-on, and on power-off.
At the last picture: the red thing at the corner is the small circuit with the tranzistor. the orange
wire is the power supply of the circuit. The 1st white one goes to the display led and the other one
is the remote out. This was a first attempt, and not the final one. The RCA cable should be thinner,
and there is no relay fitted yet. Notice that this version has two TDA output 2-channel ICs instead
of a single 4-channel, like yours probably has. If you have the previous version, note the ICs model
and tell me to give you further instructions. I couldnt find the latest pictures with the full proper
No need to say that everything you do, you do it at your own risk
Its a piece of cake, all you need to do is DO NOT RUSH. Take your time, and good luck.