Hello mmos1133,   Referring to the image on the link: #5 - e. cooling-fan connectors (6) are not replaceable. They are soldered to the system board.  
Are the fan sockets that sit on the motherboard replaceable.   My issue: Server shut down, does not power back up. Troubleshooting - out of the 6pins sets sitting on the motherboard for hot-swap plugins, only One works out of 6. All the fans works Only when plugged into that One slot on the motherboard. Are the pins-sockets that sit on the actual motherboard to plug the fans into, replaceable? Thank you in advance.
Dell Powerdge Server 720DX - issue with the fan socket that sits on the 
motherboard, out of 6 only one work