Ricoh D131 Service Manual page 512

Engine start up error
The BCU failed to respond within the prescribed time when the
machine was turned on.
SC670 D

Connections between BCU and controller board are loose,
disconnected, or damaged.

Replace the BCU

Replace the controller board
Illegal Engine Board
SC671 D An illegal engine board was detected by the firmware at power on.

Replace BICU
SM Appendix
SC600: Data Communication
2-45
CTL
CTL
D131/D132/D133