There are several brands of units similar to what you have. You could get the model number and do a google repair or comparison search. These kind of units change quite often (like computers) but you would want to have the simplest change out. Look at the camera inputs. Some units will have each camera inputed and some will go through a video selector first with only one input. Keep us posted on your findings.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7