The most likely cause of a Rectifier Comms Lost alarm is a loose connection on the communication bus for the enclosure's rectifiers. The two most common places to look for a loose connection are the following:
1) Check inside the DC Controller Shelf. The rectifier communications are passed through a cable attached to the side board, near the fuse in the rear of the shelf. Check to make sure the J1 cable is secure in it's port and does not have a damaged connector.
2) Open or remove the back door off of the enclosure and check to see if the rectifier communication cable is attached and in place. This cable should be connected to port ten on the back of the DC Controller shelf. It will be identified by splitting into two cables, which each go to the two rectifier shelves. The number ten refers to it being number ten in the line of twelve RJ45 ports, counting from the left when viewing shelf from the rear. Trace the cables to where they plug into the individual rectifier shelves and confirm the cable is securely attached to each RJ port on the side of the shelves.