I got a Panasonic car stereo radio, removable unit. Model numberCQ-E410EC. I can't get any sound out of it,s it shows the channels but no sound. I there a code for this unit for when you unhook the battery or whe n you take the unit in the house. I have a Range Rover that has a similiar un it only English and you must punch in a code to get it to work if you unhook the power source