J1A4 connector on the LSI 3ware 9750 should not be used for I2C.

This is the Install guide for the 9750: http://www.lsi.com/downloads/Public/RAID%20Controllers/RAID%20Controllers%20Common%20Files/45412-01C_9750_install_Guide_final_050610.pdf

Here

It is defined in Table 8 as 'IPMI-style' I2C. 

Do no use this connector.  For I2C support, see these KB articles:

9750 with ‘TQ’ style backplane:  http://kb.lsi.com/KnowledgebaseArticle15858.aspx