The 3.9ghz you are seeing is XFR at work, a great feature and it sounds like it is working as intended. The "fix" is to turn off Core Performance Boost in the BIOS/UEFI, you can find it in the advanced view in the BIOS, (1)advance tab (2) AMD CBS (3) disable core performance boost. Once you turn this of your CPU will run at the base clock with a much lower vcore (otherwise a R3 1200 with a slightly higher base clock).
I own the same motherboard and think I can offer some insight. A vcore of 1.4v-1.47v in BIOS/UEFI is normal if you have core performance boost in AMD CBS turned on (by default it is on). This voltage is only applied to the CPU when boosting 2 cores to 3.9ghz, your CPU will only use this boost and frequency when temperatures allow. Keep in mind that a vcore of 1.4v-1.47v will be more like 1.35v-1.4v under load (vdroop) in reality and only when 2 cores are boosting. You can test this by running Cinebench R15 and monitoring the vcore in CPU-z or HWinfo64, you will see that when using all the all the cores the vcore and speed will be much lower (something like 3.5ghz@1.23v). You will only see the high vcore and boost clock when sitting idle or using programs that that use 1 or 2 cores.
There are other nuances, the BIOS and CPU-z will read the vcore voltage from the VDDCR. This voltage is the amount that the VRM receives and is not entirely accurate for accuracy you need the SVI2 TFN reading . HWinfo64 gives both readings. A quote From the creator of HWinfo64. "CPU Core Voltage (SVI2 TFN) value is the voltage measured by Voltage Regulator, which is supplied to the CPU (as VRM output). This voltage is then reported to CPU and evaluated using telemetry functions.Vcore or VDDCR CPU is measurement of the same voltage rail, but by the mainboard logic (ITE chip). I believe the SVI2 TFN values should be more accurate. The difference between those values can be due to different measurement methods used and their impact on the readout." So while you are seeing 1.4v-1.47v in BIOS/CPU-Z you might be getting less vcore to the CPU in reality.
If you are worried about damaging your CPU from high vcore you can leave core performance boost on and enable Global C-state Control , this can be found in the same area as Core Performance boost(AMD CBS options). This allows for a more dynamic vcore, when enabled and at idle or light work loads the vcore lowers to ~0.750v to ~1.1v and then will boost when under load.
Hope this helps o7
