Inspired by the 3550 fan mods detailed here: »
[H/W] 3550-12T Fan modificationI modified the 3 fans on a 3560-24PS to run at about 60% of their standard speed by placing resistors inline on the red/power wire to each of the fans.
To do so, I used this page to calculate the resistor size needed to achieve the voltage drop for the slower fan speeds:
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www.blackfiveservices.co ··· ed.shtmlUnfortunately, my local RadioShack (I was impatient to try this) did not have the 20 ohm / 2 watt resistors I thought would be ideal, so I improvised... running three 68 ohm / 0.5 watt resistors in parallel does approximately the same job as a single 20 ohm / 2 watter.
If even of the fans rotates too slowly, the 3560 will compensate by kicking up the speed on the other fans into overdrive (you hear this same speed when the switch boots, its quite loud)... so I also chose to splice the blue and black leads together to eliminate the switches ability to see the slower fan speed that I was intentionally forcing upon it.
As an aside, if you want to see this behavior in action, you can simply gently press your finger against one of the fans to slow its rotation and hear the 3560 kick the other fans into high gear... and if you are like me, you can also test the "bypass" behavior (before cutting wires!) by unplugging one of the fans from the motherboard and jumpering the blue/black pins to see that this indeed makes the 3560 ignore slow and/or dead fans.
So all in all, $3 of of resistors at the local Radio shack, plus a couple of feet of electrical tape, and about an hour of your time can make your 3560 run virtually silent - which for any low volume home office application should be quite safe to do and much easier on the ears.
Cheers and Happy Modding!