Bristol Babcock BSAP Communication Problem

I have a Bristol Babcock (BB) 3330 CPU with a BB Communication Board. Port A on the communication board is set up as a custom port for modbus communication back to the HMI (National Instruments Lookout)software computer and port B is set up for BSAP communication. Recently, a problem has occurred with the communication involving the BSAP port. When I look at the modbus communication statistics in the HMI software we are getting a lot of CRC errors when both ports are connected. However, if I unplug the cable from the BSAP port the communications are excellent (CRC errors = 0). I have replaced the cable going to the BSAP port and swapped out communication boards but the CRC errors still exist.

Does anyone have any idea what might be causing the CRC errors and what other methods I can try to resolve the issue?

Thanks for any response.

Jason Phillips
SCADA Manager