^^^ out of curiosity, do you know the code for the radio pictured? Or how the diodes map to the code?
Google image search finds a Russian website as the source of the code:
Порядок ввода PIN KODа для разных моделей магнитол. Раскодирование магнитол VOLVO. Заказ PIN KOD.
www.volvo850.ru
Translating to English with Google Translate:
"The photo shows an example of coding radio CR-603, PIN KOD 2214."
Apparently it's not a straight binary number - each digit is coded individually and the locations of each binary digit are somewhat scambled. There's a table on the website which shows the arrangement. The table is kind of awful and so is the translated Russian, but I've managed to decipher it I think.
In this particular case:
Digit 1: Diodes 10, 11, 12: 010
Digit 2: Diodes 6, 7, 8: 010
Digit 3: Diodes 2, 3, 4: 111
Digit 4: Diodes 1, 5, 9: 100
So decoding the binary:
2 2 7 4
But also according to this Russian, "111" in the matrix is actually "1", not "7" ("000" is 6 and "001" is
also 1, FYI) so the final code is:
2 2 1 4