Fan measurement issue (unsure if Mobo or hardware related)

[docbrown]

Hi,

I hope this is an appropriate place to post this question. Please excuse, I'm a n00b, but haven't been able to find an answer to this question anywhere.

I've built the system detailed in sig below, but am getting some strange behaviour from the chassis fans, which I have to assume is motherboard related. I am running 3x stock 140mm fans into chassis headers on a Z77 Sabertooth mobo.

My problem is that the fan speeds reported are totally unrealistic, both in UEFI and Win7 (ASUS Suite II). Over a period of a couple of minutes, any of the chassis fans might spike (from ~700RPM to ~20,000RPM, which is impossible), this lasts a second or two then returns to normal. Voltages look OK, with the exception of VCore which is bouncing about all over the place. I'm not sure how much this should be happening when I reckon I've restricted the processor to 3.5GHz in the BIOS.

As an aside, I don't think I've seen CPU, CPU OPT, ASSIST 1 or ASSIST 2 fans playing up.

My question is: does this sound like a dodgy mobo, and should I RMA? Also, as an aside, Win7 ASUS diag reports maximum RAM bandwidth is 667MHz:- does this sound right?

This is the first system I've built in 10+ years and so far I'm happy. The ultimate goal though is to overclock, but I'm not confident in cranking up the speed yet until I've got a handle on this.

Thanks in advance,

Calum.

-------------------------------------------------------------
i7 3770K @ 3.5Ghz - 16Gb Corsair Vengeance DDR3 @ 1600MHz
Mobo Asus Sabertooth Z77 BIOS 1504
Corsair Obsidian 800D with AX1200 PSU
Corsair H100 H20 Cooler
OCZ Agility 3 120Gb SSD

 

[RJC]

That's normal, mine in the past have spiked up to show ridiculous speeds.

I am not sure what happens but I think when the fan slows down the speed sensor throughs out a silly reading which the motherboard picks up and shows high speed, rather than showing 0 rpm which happens on some other model fans.

On the ram you need to double what the reading shows, so at the moment your running at 1333mhz, you need to pop into the BIOS and adjust the timings and speed.

 

[docbrown]

Thanks for the info RJC: I can sleep well now (or at least start pumping the overclock up...)