I just purchased 2 of these fans,
http://www.amazon.com/gp/product/B00A6Z0AS6/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1The specs are comparable to the original fan and make a good replacement or secondary fan. I installed them as secondaries. Even though the connector is 5-pin it will still connect to the 4-pin header with no modification to the connector. The pins will need to be rearranged though to match up correctly with the pins on the antminer. I didn't have long screws to attach it so I just pulled 2 from the existing fan. Don't tighten the screws completely or the fan blades will brush up against the antminer. Leave them loose or add a grommet between the fan and the antminer.
http://i57.tinypic.com/2004vma.jpgI would like to add a second fan. I found a good one but the connector is differnt. Maybe I need to change it also. I need to know the pin layout from the Antminer.
