Solution:

Due to some mainboards which inside the PPC don't provide the -12V to the riser card, so the RS-232 mode of PCL-746+/PCL-849 CAN NOT WORK. Please do confirm the BIOS version of PPC to clarify the doubt. Only the version 2.21, 2.22 and above have offer the -12V to the riser card. You can find the information while power on the PPC. If you do meet such problem, you can order the -12V convert kit (P/N : 9692-001-000, PPC-001) to overcome this problem.