Disabled car radio in anti-theft mode!?

Discussion in 'General Electronics Chat' started by PaulEE, Aug 1, 2013.

  1. PaulEE

    Thread Starter Member

    Dec 23, 2011
    Hello all,

    I recently purchased a 1986 Mercedes 560 sl. This car came equipped with what my research shows to be a "Becker Grand Prix model 754" radio. When I received the car, the radio had four dashes on the LCD display and the buttons were inoperable.

    After many hours of research, I came to the conclusion that the radio plugs into the anti-theft system of the vehicle and has a built-in mercury battery. When a thief steals the radio, the battery is supposed to die a short time thereafter, triggering the radio to disable itself. This particular model does NOT have a code.

    My research also allowed me to find a description of what the dealership "reset tool" looks like. It apparently plugs into the face of the radio (there is a small header between the guts and the faceplate interface/display). The device has a red and green button - pressing the buttons in the correct sequence "resets" the radio.

    My question is this: does anybody have ANY IDEA what these buttons might be doing? does anyone have any information on these radios? schematics? shop manuals? assembly/disassembly diagrams?

    The radio is sitting beside me. It has both horizontal and vertical circuit boards that fit together and are soldered. It was very obviously built in such a way as to be near impossible to get apart easily for reverse-engineering/hacking/fixing/battery replacing/etc...I've also read that Mercedes and BMW stay quiet about it - I'm sure it's a money maker due to people like me wanting original equipment in their cars.

    If anyone has ANY other information, I would appreciate it. My goal at this point is to figure out what they're doing with their "reset tool". I'm sure they're just holding the processor in reset with the first button, applying one voltage or another with the second button, and then releasing the processor from reset again, but I have no idea.

    Any info would be much appreciated.
  2. WBahn


    Mar 31, 2012
    Have you contacted a dealer? Often dealers will reset a radio for free.

    As for what it is doing, that is anyone's guess. If I were really wanting to make it hard to reset the radio except by an authorized party I would have the tool have a signed digital certificate and have the radio only accept commands that are properly authenticated via a digital signature.
  3. PaulEE

    Thread Starter Member

    Dec 23, 2011
    This is what went through my mind. I called one dealership this morning and they claimed they no longer had the tool. I'll try another tomorrow. I think I'll have no choice but to send it to Becker Autosound to "fix".