Asus M4A78-HTPC/RC: A Complete HTPC Solution?

CPUs|Motherboards
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AM3 CPU Power Consumption

In our M4A78T-E review, we noticed a significant power consumption discrepancy of up to 22W when using an AM3 CPU on an AM2+ motherboard. Unfortunately the M4A78-HTPC/RC is also afflicted by this anomaly, so it doesn't appear to have been an isolated case.

Power Consumption: Phenom X3 720 (AM3)
Test State
M4A78-HTPC (780G AM2+)
M3A78-T
(790GX AM2+)
M4A78T-E (790GX AM3)
Idle
54W
56W
54W
VC-1
~91W
~91W
~71W
CPU Load
147W
131W
117W
CPU + GPU
Load
162W
157W
135W
Systems configured with 2GB of RAM and 256MB IGP memory.

Using a Phenom II X3 720 processor, our test configuration's idle power was similar to 790GX based M4A78T-E (AM3). Once any type of stress was placed on the system, the board drew significantly more power as measured from the wall. During video playback, we measured a 20W difference. This figure expanded to 30W when the CPU was placed on load. The results were similar to what we found with the M3A78-T, only the difference was even more pronounced, possibly due to poorer power regulation. We've always found that high TDP chips tend to generate higher power consumption on budget chipsets lacking in VRM cooling.

Cooling

Lower cost boards ship with simple heatsinks on the northbridge and southbridge while those targeted at enthusiasts typically have large heatpipe coolers and heatsinks on the voltage regulation modules near the CPU socket. A well-cooled motherboard can deliver better power efficiency and stability.

Heatsink Temperatures
Measuring Point
X2 4850e
X3 720
SB Heatsink
45°C
53°C
NB Heatsink
51°C
66°C
VRMs
50~55°C
80~90°C
Measured with a spot thermometer after 10 minutes of full CPU + GPU load. CPU fan reduced to 6V.

The cooling on the board was very good when used with the X2 4850e processor. The hottest spot on the northbridge and southbridge heatsinks measured 51°C and 45°C respectively, while the VRMs registered in the low 50's. With a Phenom II installed, we recorded significant increases in heatsink temperature, though we could still place our fingers on them comfortably for long periods of time. The VRMs, on the other hand, were burning hot — some extra cooling here would not be amiss.



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