51 Capacitor volts are too low before line contactor closes.
52 Traction or pump motor speed sensor error.
53 Traction controller does not respond to master controller.
54 Pump controller does not respond to master controller.
56 Mini-lever module or joystick cannot communicate with master controller.

For starters:
check your control and main buss fuses(dont just look at them or use a ohm meter, do a resistance test across the fuse element, it should be close to 0 resistance, anything more may indicate a problem inside the fuse)
also check the power cable connections
check the cable connections on the controllers, look for any melted or corroded areas.