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COOLING THE CPU, NB & VRM: THE REALITY
It was a pretty good plan, and it would have worked if I
hadn't given in to the dark side and started overclocking heavily.
This required boosting the CPU core voltage, which in turn boosted the
power consumption radically, into the vicinity of 100W. As
with my old 830D, this much CPU wattage meant unacceptably loud fan
speeds to obtain reasonable temperatures with an XP-120.
Since I already had in hand a Scythe
Ninja heat sink and matching duct from my previous
build, I switched to that heat sink, which I knew for certain could
cool the CPU quietly. The Ninja is huge and efficient. Here is a photo
from its SPCR review.
The Scythe Ninja tower heat sink,
with a 120mm fan attached.
While running the CPU at high voltage, I noticed that the VRM
was
getting pretty warm, though not nearly as hot as on my old
motherboard.
Still, it was hot enough that the heat pipe to the north bridge
was actually working backwards: it was transmitting heat toward
the north bridge instead of away
from it.
My stockpile of earlier experiments contained a Thermalright
HR-05
tower north bridge heat sink, so I decided to try it instead of
the stock heatsink/heatpipe/radiator thingie. This was not particularly
easy because although the HR-05 comes with a clip designed for
Intel-style hoops, it is designed for hoops on
the northeast and southwest sides of the north bridge. For some
bizarre reason, the P5W DH has provision for all four hoops but only
has two of them populated: the northwest and southeast ones. Mounting
the HR-05 required severe bending of the clip to reverse the angles,
since I didn't want to take a soldering iron to this insanely expensive
and hard-to-get motherboard.
When mounted as designed, the HR-05 can be rotated to various
angles
as needed. In my reversed orientation, the attachment clip bumped into
the bottom fins, and prevented this rotation. To address this, I
cut notches in the bottom two fins, as shown in this (very
blurry) close-up photo.
Notches in the bottom fins of the
HR-05 allow it to be rotated.
The HR-05, though billed as a passive heat sink, does need
some airflow to cool an overclocked 975X. Also, since
the Ninja is a tower heat sink, there is no downward airflow onto
the VRM from its fan. Fortunately, the fan on the Ninja can be
positioned so that it pushes some air between the Ninja and the
motherboard, and also between the Ninja and the HR-05. To capture as
much of this air as possible, I angled the HR-05 with respect to the
Ninja. This close-up shows the fan and the two heat sinks.
The CPU fan spills some air onto
the angled HR-05 heat sink.
Because I planned to duct the CPU heat directly out the back, there needed to be a top case fan to cool the rest of the motherboard. To minimize
noise, I wanted to soft-mount this fan, but the P180 case is
not designed for soft-mounting a top case fan. The top fan mount has
two screw holes
at the back, but at the front instead of screw holes it has
two bent metal tabs to hold the
edge of the fan. I got around this by breaking off those tabs and
drilling two new holes. This is easy, since this part of the case is
plastic. Just use a fan as a drill guide. I soft-mounted the top fan
with an AcoustiFan
gasket. After cutting out the grill to reduce noise and
mounting the fan, the P180 spoiler still fits in place, and looks like
this:
The P180 top spoiler fits over
the soft-mount screws to keep fingers and paws out.
Here is an inside view
of the CPU and north bridge heat sinks installed, together with the CPU
and top case fans.
Ninja CPU and HR-05 NB heat sinks
installed, with CPU and top case fans.
When the CPU fan is positioned flush with the heat sink fin
closest
to the viewer in the photo above, it intrudes into the first DRAM
slot. Since I have only two DIMMs, this is fine. I use the black
connectors, which are farther from the CPU.
The sides of the Ninja line up very well with the case
openings,
making ducting of its exhaust air very simple. This was mandatory in my
old configuration, and still worthwhile in my new one. The duct I use
has four flat panels, two long and two short. The long panels seal the
top and bottom sides of the Ninja and force the air out the back case
opening, which is sealed with some foam strips (these also bear some of
the weight of the Ninja, its fan, and the duct). You can see the foam
strips on the left in the photo above. Here is what the finished Ninja
duct looks like, as viewed from the back of the case.
Ninja duct (rear view), with its
foam lining.
The back portion of the duct is lined with thin (4mm) foam.
This is
not neccessary with a slow fan, but when I first built this duct I was
using pretty fast fan settings and wanted to absorb some fan noise. The
duct slips over the Ninja and nestles in the foam strips at the back of
the case, like this:
Ninja duct installed in the
system; air still gets to the HR-05.
Like all of my ducts, this one is made from styrene, a stiff
plastic that is very easy to cut and glue. You can find a tutorial here
(posted by a guy in my home town!).
The base of the Ninja (below its fins) stands two inches above
the
motherboard. My duct covers only the fins, so it is possible to force
air between the duct and the motherboard, with the effect of cooling
the VRM. The approach I use to do this is to pull air across the board
with the top case fan. To direct this air flow properly, I built a
two-panel baffle that mates with the Ninja duct and
the case walls to seal off all other paths to the top case fan, as
shown in this photo.
Baffle to force top case fan air
flow across VRM.
Here is what it looks like installed, with its edges tucked
into some foam. As you can see, the only way
for air to get to the top case fan is from the area around the base of
the Ninja. This cools the VRM.
VRM baffle installed, together
with Ninja duct.
Because the Ninja and HR-05 are remarkably efficient, and the
exhaust air is ducted directly out of the box, only the gentlest of
breezes is needed to cool the CPU, north bridge, VRM and DRAM.
So with two fans, two monster heat sinks, and a couple of
ducts, the top third of the system is take care of.
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