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I've noticed the same thing on the few boards (DB75EN / DQ77MK) that we use as well, although I think the fan ramp-up is caused by the heatsink fan itself. Assuming you are using the boxed processor heatsink, keep your eye on the fan when power is applied, it 'twitches' twice, then ramps-up.
This doesn't happen on all processor / mainboard combinations that we use. I believe the ramp-up is caused by either the Delta or Nidec fans, but I can't remember which off the top of my head. Foxconn fans contained in the retail boxed processor package don't seem to exhibit the ramp-up.
Although at first I did not believe that the fan itself could play a part here, you are absolutely right! I finally had occasion to try an off the shelf PWM fan connected to the CPU fan header and it did NOT exhibit the behavior in question.
The larger question then is: is there an alternate fan for the i5-3570 which does not exhibit this behavior (and will Intel exchange them under the boxed processor warranty)?
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There are different heatsink/fan vendors for the boxed processors, but I'm not sure if you'd be able to specify an accurate replacement, as they seem to use the same AA#. I tested a few fan/heatsink units that we had in stock for varying processors, and it seems that the Nidec fans are the only ones causing a ramp-up.
I have exactly the same problem with an Intel / Nidec CPU cooler supplied with a Pentium G840 (LGA 1155) Sandy Bridge processor.
Upon power on it twitches a couple of times as the original poster mentioned and then revs / ramps up to 100% for a few seconds. After that it settles down to a reduced speed and appears to run as normal.
The above picture is of the actual fan I have fitted in my PC.
When I first fitted the CPU / fan combo I had just built a new system and initially thought I had a problem with one of the other components. After extensive swapping of parts and troubleshooting, including speaking to Intel support, I eventually decided it must be a faulty fan after swapping it for another Intel fan made by a different manufacturer.
After finding this thread which seems to indicate that there are more of these fans exhibiting this behaviour, is this normal for these fans to operate in this way? Can somebody at Intel confirm this?
I found a PDF on the Nidec website which lists the model as a cooler designed for the 1156 socket and refers to it as PWM and temperature controlled but makes no mention of it ramping up speed when switched on. The instructions that came with the processor hardly give any information on what fan you are dealing with.
As the original poster mentioned:
"This is behavior we usually associate with server boards or desktop boards with a "detect fans at next boot" function"
Are these coolers designed for a 1156 board more suited to server applications where the start-up noise is not relevant?
I'm only a casual PC builder so don't know the answer to the above question but am figuring if designed for a server board, the ramp up would not be such an issue but when used in a home PC being switched on and off regularly, it becomes quite intrusive and suggests a problem [when there probably is not] as most PC's don't make a noise like that at start-up.
I know one thing for sure, I need a different cooler!
Message was edited: Original message had incorrect link to fan part number. [F90T12NS1A7-64***A* now removed from text] Correct datasheet for fan is Nidec F90T12NS1A7-64***B* - www.nidec.co.jp/product/fm/pdf/heatsink-018.pdf Listed as a LGA 1156 cooler / variable speed fan. Note datasheet is for a generic fan of this type.