falla ricoh aficio 551 310-311-320-321

Hola, tengo codigo de falla -sc 310-311-320-321-, esta funcionando correctamente y con el corre de las copias va tirando esto codigos

Aqui envio informacion te pueda servir, observa las posibles causas, y comentas.
SC310: Potential sensor error 1
Definition- [C]
When calibrating the drum potential sensor at the process control initial setting,
the drum potential sensor output voltage is out of specification.
- Possible causes -
• Potential sensor defective
• Poor connection between the potential sensor and the I/O board (IOB)
• IOB defective
• Poor connection between the drum unit and the I/O board (IOB)
• Development power pack defective
SC311: Potential sensor error 2
Definition- [C]
When calibrating the drum potential sensor at the process control initial setting,
the rate of change of drum potential sensor output with voltage on the drum is
out of specification.
- Possible causes -
• Potential sensor defective
• Poor connection between the potential sensor and the I/O board (IOB)
• IOB defective
• Poor connection between the drum unit and the I/O board (IOB)
• Development power pack defective
SC321: No laser writing signal (F-GATE) error 1
- Definition- [D]
The laser writing signal (F-GATE) does not go to LOW for more than 15 seconds
after the copy paper reaches the registration sensor.
- Possible causes -
• BICU board defective
• Poor connection of the printer controller
• Printer controller defective