I have one unit I thought the fan was bad on as well. I'm not sure if the damage is in the fan itself or the board, but for whatever reason the PWM doesn't seem to work. Taking a small flat head screwdriver and pushing down the locking pin on the blue wire of the fan connector allows you to pull it out, which will cause the fan to run at full speed. That solved my issue.
Great. Thanks. Both now OC to 400MHZ and running at 40 degrees. Let's hope the fans last a while!
I wish Bitmain would publish a way to SSH into the S1 (as we do for OC) and set a target temperature so I can set to say 45 but I'm guessing this might me more crudely done with the hardware.