"Gary Brown" wrote in <
news:aHnVj.486$dP3.420@newsfe02.lga>: > Hi,
> A newly installed CPU heat sink and fan prevented my PC
> from running. The PC started up then turned itself off after
> a few seconds. The HSF appeared to be seated properly
> with more than adequate heat sink compound. The heat
> sink was considerably larger than its predecessor but no
> shorts to adjacent components were apparent. I put the
> old heat sink back on and the PC runs again. Any clues
> why this could happen?
> The new HSF is a MassCool 5F263B1M3 and replaced
> the stock AMD unit. The CPU is an AMD Athlon 2800+.
> Thanks,
> Gary
For the new fan and heatsink, is the new fan a 3-wire or 4-wire fan?
Are the 3 or 4 pins on the motherboard header marked "CPU" to which you
are connecting that fan?
Intel decided to come out with a newer scheme to control fan speed. The
old scheme was use change the duty cycle for the fan controller in the
super I/O chip. That's how, for example, Speedfan and Motherboard
Monitor worked to control speeds for 3-wire fans. The new scheme uses a
separate control line to monitor the temperature and decide the speed of
the fan rather than old duty cycle (pulse) scheme the power on and off
the fan.
I believe a 3-pin fan will work with a 4-pin header but you need to be
sure to align the pins correctly. The result is that the sense wire
from the fan will be seen by the BIOS to know the fan is spinning but
you will not have any control over the fan's speed (i.e., it will always
spin a max RPM and always be noisy even when a slower RPM could be used
to sufficiently cool the CPU under less than max load).
http://www.intel.com/cd/channel/reseller/asmo-na/eng/299984.htm
http://www.intel.com/support/motherboards/desktop/sb/cs-012074.htm
http://www.intel.com/support/processors/xeon5k/sb/CS-022300.htm
http://tinyurl.com/6zznx7 (Google Groups copy of my prior post)
The problem with the old 3-wire, super I/O, power duty-cycling scheme is
that it could faster burn out the windings in a fan because of a higher
inrush current when the fan got restarted (when the power pulsed on).
Some fans aren't designed for that mode of operation. It was also not
accurate for controlling speed, especially when you got down to 5%, or
less, for duty cycle; for example, I can go down to 3% on my CPU's fan
so that it is sure to start spinning (has enough current) and to keep
spinning but below that and the fan might not start or it will stop. So
I run at 5% duty cycle to make sure it keeps running okay at a minimum
speed.
You might have a new 4-wire fan that won't work on a 3-pin header. You
might have a new 3-wire fan but mispositioned it on the 4-pin header.
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