TomTom GO520 not charging?

Help.
My 520 will charge in the cradle connected to the pc but not in the car. I have tested the charger and get around 8 volts . I inadvertently pluged in a speaker jack plug to the charger socket on the 520, after this it will not charge.
I notice that the 520 charger has an outer metal cover and a hole in the center. The speaker jack plug is solid. Is there supposed to be a center terminal post inside the 520 charging port and could i have bent it over or something. If so, can i get to it to sort the problem.
Thanks.