As Andrew said, check to see if it has a Crystal, it may look like a plastic rectangular cover with either 27MHz on it or with a frequency on it like 27.365Mhz. When you say Broken, do you mean Physically or electronic? Sometimes there is a small wire attached to the antenna that if turned too many times or just turned can break the wiring to the antenna, making the unit seem like it's broken... Also check Battery levels and orientation, some of us have been known to put dead batteries in backwards before (I wont go into details about my faults
) If the batteries were put in backwards and the circuitry doesn't have reverse polarity protection, it could have fried something inside, hopefully that hasn't happened.
Just a couple of things to check.. Also check the trucks batteries and wiring, they take a fair amount of punishment, but only takes one bump to break em.