AOpen's Core Duo Flagship i975Xa-YDG motherboard

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HEATSINKS AND COOLING

The best thing about the i975Xa-YDG for SPCR enthusiasts is that AOpen has fitted it with a standard socket 478 desktop heatsink retention bracket (and four-bolt standard plastic backplate), rather than cripple it with a too-small, proprietary heatsink mount system that dictates the use of a small, too noisy fan. This means that most aftermarket socket 478 heatsinks can be fitted without problems, giving users a huge range of capable models to choose from.


CPU socket sits diagonally in 478 HS retention bracket.

It is important to keep in mind that the absence of a heatspreader has several ramifications (exactly like the Pentium M, as originally researched and reported by Ralf Hutter in SPCR's first review of Pentium M boards for the desktop):

  • The top of the CPU sits approximately 0.075-0.078" lower than a standard P4 or Celeron 478 with a standard casing (with heatspreader). The base of the heatsink, therefore, must be smaller than the curved-corner area defined by the inside perimeter of the plastic heatsink bracket. Otherwise, the bracket itself can prevent the HS base from making contact with the CPU die.
  • Lower CPU core height with a P4-478 heatsink will result in reduced pressure. However, the standard P4-478 casing has a recommended clamping force of 75lb/ft ± 15lb/ft, while the Core Duo / Solo datasheet calls for a maximum of 689KPa, or 14.4lb/ft. pressure. So the 0.075" lower height might be a good thing after all.
  • It is best if the HS mounting mechanism can apply tension gradually, rather than all at once, as with the typical clip. Uneven tension, too high a tension, or tilting the heatsink against a CPU die edge during mounting should all be avoided; the edges of the bare die can be chipped, which could mean the death of an expensive processor. This means the screw-down heatsinks such as the Zalman 7000, 7700 and 9500 series are a bit safer to mount than more conventional dual-clip designs.

A low profile all-aluminum heatsink with integrated 70mm fan is provided with the motherboard. It's small even compared to the stock HSF that came with the first retail packaged P4 over four years ago. It is probably perfectly adequate to cool any of the current Core Duo processors, which are rated for 31W TDP. Standard metal tension clips that require very little pressure are used for simple installation.


Low profile CPU cooler provided with the i975Xa-YDG.

The worst thing about the i975Xa-YDG for SPCR enthusiasts is that AOpen has fitted the Northbridge chip with a small heatsink and matching fan that promises to be annoying. It's just too small for it to give any cooling without spinning fast enough to make a high pitched tone. This is a change from the lab sample board, which had a similar size heatsink but was not equipped with a fan. The southbridge chip, on the other hand, has no heatsink at all.


NB cooler with wee fan; SB is bare.

An intelligent cooling decision was made regarding the positioning of the two PCIe X16 slots. They are separated by the width of two slots, which is nearly 3 inches. This means if the dual-card Crossfire mode is used, both graphics cards can be fitted with the large heatsink / fans that are critical for good cooling with low noise.

BIOS

The Phoenix Award BIOS (version 1.03 dated April 4, 2006) is surprisingly basic for a board with such high aspirations. This is not to say that it is a limited BIOS, as clock speed adjustments are provided for CPU and PCIe, and voltage adjustments are available for CPU, memory, northbridge chip, and PCIe. The memory timing settings also have their own submenu, which is quite extensive. The range of settings provided for many parameters is large and extremely fine, as show in the table below.

BIOS Adjustment Range
Parameter
Voltage
Clock
CPU
0.7375 - 1.5V
in 0.0125V increments
166 - 199 MHz or 200 - 320 MHz in 1 MHz increments
DRAM
1.80 - 2.15V
in 0.05V increments
533 / 667 MHz
NB
1.525 - 1.675V
in 0.05V increments
-
PCIE
1.5 - 1.7V
in 0.05V increments
100 - 160 MHz
in 1 MHz increments

However, the Power Master feature is a simple Off / Auto switch, and there is no sign of AOpen's SilentBIOS or SilentTEK intelligent fan controller. Many previous versions of these features (in other AOpen boards) were extremely flexible, with a large number of user options. Perhaps, as with some of AOpen's other MoDT motherboards, the attitude is that with the CPU thermal envelope so low, there's little benefit to having complex fan and power management schemes.

The function of Power Master is not fully explained in the manual or in the BIOS help menu. The manual states,

"When the processor loading is heavy, Power Master will raise your processor's clock frequency to meet your requirement. On the contrary, when the processor is in low loading, Power Master will drop the clock frequency to reduce the noise from the processor fan."

By carefully monitoring system states, it became clear that when Power Master was set on AUTO, the CPU clock speed dropped by 20% at idle, and increased by 8% at full load. This is documented in the testing section.



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