AMD Ryzen 9 3900X Tested on Cheap B350 Motherboard 79

AMD Ryzen 9 3900X Tested on Cheap B350 Motherboard

Conclusion »

VRM Temperatures

Considering the ASUS B350 only has a very basic 4+2 VRM configuration, we expected a lot of current to flow through those phases.

That's why we were curious about how the VRM was holding up, which had us get out our FLIR thermal camera.

Air-Cooled CPU

We start VRM testing with the Noctua air cooler and the CPU running at stock.


With the system sitting idle at the desktop, at stock clocks, VRM temperatures reach 66°C, which is mostly because of heat in the top right coils for the SOC voltage. The coils for CPU core voltage remained cool.


Next up, a purely single-threaded workload—Super Pi. As you can see, the hottest part of the VRM circuitry goes up to 88°C—no problem.


I also wanted to try some gaming, so I fired up Battlefield V and waited for the VRM temperatures to stabilize—a little higher than single-threaded Super Pi, but nothing to worry about.


As a multi-threaded test, I used Blender, which fully loads all cores and manages to drive VRM temperature up to 108°C.


In order to test VRM temperatures with overclocking, I set 4.0 GHz all-core at 1.20 V (the highest our CPU and air cooler can handle), and temperatures went up only marginally, which isn't surprising. The CPU at stock runs something around 4.0 GHz 1.2 V, too.

Power consumption is what drives VRM temperature, so if some manual setting uses roughly the same CPU power as the stock default, it's normal to see the same VRM temperature.

Water-Cooled CPU

Let's see what happens when we use a 240 mm AIO instead of the Noctua.


At stock, temperatures are the same as with the air cooler.


Here, we are playing Battlefield V on the system—things are heating up now: 116°C.


With our multi-threaded Blender load applied, the VRMs reached 130°C, but the system did not crash and chugged on perfectly fine. As we've seen, this seems to be the point where some sort of throttling starts to ensure nothing gets damaged by the heat.


If we overclock the CPU, too, to 4.0 GHz at 1.225 V, VRM temperature goes way above what these coils are rated to handle, reaching 138°C and higher. Once 140°C is reached, the CPU will reduce its clock speed to 550 MHz (no matter how many cores are active), which immediately drops the VRM temperature well below 140°C.
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