Let me explain, then, why I said that. I have seen four different types of mobo fan headers.
1. 3-pin fan headers can only operate on Voltage Control Mode. This mode can power and control both 3-pin and 4-pin fans, because 4-pin (PWM) fans have a backwards compatibility feature that allows them to work like this. Controlling a PWM fan by Voltage Control Mode is not really ideal because it fails to use some of their advanced features, but it does work.
2. 4-pin fan headers that can only use PWM Mode. This one-mode system is part of the BIOS software as well as of the mobo hardware and it cannot be changed. This header type is perfect for 4-pin fans. But any 3-pin fan plugged into this header type can only run full speed all the time, with no control.
3. 4-pin fan headers that can be used in either control mode. Typically these are set to use PWM Mode by default (but many are set the other way) and you can change the mode manually to Voltage Control Mode (aka DC Mode) in BIOS Setup. This latter mode will control 3-pin fans AND 4-pin fans, but you are better advised to use PWM Mode for 4-pin fans. A handy variation of this is a header of this type but with an additional feature in the BIOS software that allows the header to determine by itself what fan type is connected, and change its mode automatically.
4. 4-pin headers that actually never use PWM Mode, and use only Voltage Control Mode (aka DC Mode) always, never sending out a PWM signal on their useless Pin #4. These have become very common on mobos today. Why? It seems putting 4 pins on the mobo is easier and makes the user happy. PLUS, this mode CAN power and control either fan type, even if it is not quite ideal for PWM fans. Its only problem for a user is that, lacking the PWM signal, it cannot be used with a 4-pin fan HUB that must have the PWM signal to work.
On mobos, almost all use for the CPU_FAN header the type 3 above - capable of controlling either fan type, and sometime using the automatic fan detection feature. But for the case fan headers, any of those types might be present, and the manual is usually helpful in discerning which type.
From OP's original post and the manual for the mobo, the labels on the two mobo CHA_FAN headers indicate they use PWM Mode. In the brief description of fan controls in the BIOS Setup screens, it shows a control to choose whether to use PWM Mode or DC Mode for the fan whose options you are setting. This would be entirely normal for the CPU_FAN header. It does NOT show, nor does it say anything about, whether or not that same option exists for the CHA_FAN headers. So either is possible. IF the CHA_FAN headers also can be set to DC Mode, that makes then type 3 (above) and they can control 3-pin fans. However, if that option does not exist, that makes them my type 2 (above) and they can NOT control the speed of 3-pin fans. Based on the labels shown in the manual, these headers are not my type 1 or my type 4 (above).
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