You might try seeing if you broke the connection on the pin (Pin 1) to the PIC that handles the PWM to the LEDs. I'm not sure which one it is on there (ISTR it is the PIC nearest the buttons but not positive on that), but there are only two. Once you find it, you can retouch that solder joint and it may be back in business. We've seen bad solder joints that have contributed to the controls on the display board going dead, so perhaps this is what you have here. Since you say it was dropped, it makes it even more likely.

Good luck,
Stu