Hashem.M

You can skip all the explanation gibberish and Go straight for the first step I tried to make it as clear and organized as possible
One of the first things i attempted On the W210 is the aux conversion, because simply the radio sucks !
On the Daewoo Nubira and the Hyundai Santafe there were three pins labeled L-GND-R To remove and replace with the aux input, which made the job very easy, but this damned becker had nothing,

i decided -using the service manual- to solder the aux input on the Processor ic's Output (pin 7 and 24), but the volume was too low

so i connected it directly to where the tape head connected , but the gain was really high ! and all i got was distortion (basically sounded like crap)
since the output voltage from the phone was higher than what the processing Ic is expecting (phone output is close to 1.5volts and the head's output is in millivolts ) so i decided to lower the input voltage using a simple voltage divider and this is how i did it

A-Getting the Becker out
(Make sure you have the headunit's code, though it can be acquired online using the units serial number)

A1-i used a two nail clipper instead of the special keys

the clippers file (or what ever its called) is inserted in the hole and pushed outside while pulling the tape outward ( i used only one and kept alternating between the holes
how the lock should be pushed inside using the file.


A2-After Pulling the headunit out, i removed the connectors and the antenna cable.



B-Disassembly and modification.
B1-The units model is be 3100 which was used to get the service manual.


B2- the top cover is pried from the back using a flathead.


B3-After removing the Four Torx 8 screws holding the cassette player, the player is pulled out.


B4-Cassette head's cable is removed using a soldering iron.



B5-Aux input cable is soldered instead of the heads output and pulled from the back and whole unit is reassembled .




B6- Two 50k seperate potentiometers for each channel and two 150k ohms resistors are used to make the voltage divider circuit(used this www.falstad.com/circuit/ for demo).



C-Assembly and testing
C1-Drilled a hole in the cubby for the aux 2.5 trs wire and connected the headunit.


C2-The phone is connected at lowest volume and the headunit at normal volume, and a cassette is inserted to fool the headunit that there's a cassette playing .

C3-The volume on the phone is raised slowly and the potentiometers are tweaked to reach a good level for playback.
C4- Headunit is put back in its place .

C5- Enjoy your favorite tunes.

Two additional things can be done here:
1-The pots can be hidden inside the headunit, for there is plenty of space for this
2-The resistance of the pots after tweaking can be measured and replaced with constant value resistors.
but i like to be able to tweak them any time i want so this is what i ended up with .
3- The eject can be desoldered so that nobody can remove the cassette after insertion