What is the cause of this situation:

After switching off the ignition the radio memory reset and i need to enter the pin code....

My ideas:
- memory circuit board fail
- some extra battery on the radio board
- voltage peak after ignition switch off



Wiriing is good:
1 - 0 Voltage (ground)
2 - Ignition
3 - illumination (+12V)
4 - constatn +12V

 

I would suspect maybe you are losing the circuit 30 (constant 12v). I would make sure the constant hot is always there but if so maybe there is a battery or capacitor on the board like you stated. Still should be an easy diag and fix

 

Try the guys in NJ who specialize in Beckers radio. I just sent my old one to be repaired for my 1991 190 E. I found them on Ebay by searching for Becker Radios Good luck.