Changing motherboards - misc questions

I'm about to replace the motherboard in an old PC (thread here) so I've been looking at the old PC's wiring. I'm puzzled. The PC has 3 fans (outside of the PSU) - the CPU fan and 2 case fans. The CPU fan cable is plugged into the CPU fan header as expected. The two case fans are connected to a cable to the PSU with a molex plug. One of the case fans has an additional wire going to pin 3 of the SYS_Fan1 header. On this MB - a Gigabyte GA-X58A-UD3R) the SYS-FAN1 header has only 3 pins so I think there is no speed control available.

Is there anything wrong with this configuration? I kind of like the idea of fan power being delivered directly from the PSU rather than being routed through the MB. And I really want to avoid any re-cabling if I can avoid it ... even if that re-cabling is just inserting wires into a new plug. However, the new MB - ASUS Prime H370-Plus - all 3 SYS_FAN headers provide speed control. Is it worth rewiring to use that control?

Another question.
The cable from the front panel audio has two daisy-chained connectors. One is plugged into the front panel audio header; the other is just sitting there. Any idea what the 2nd plug is for?

I would use the fan connections on the motherboard. I'm doing that on my ASUS ROG motherboard and no problems.

On the Audio connectors, probably one is labeled "HD Audio" and the other "AC 97". Use the HD Audio as it has jack sensing that the older AC97 does not have.

fireberd said:

I would use the fan connections on the motherboard. I'm doing that on my ASUS ROG motherboard and no problems.

Hmm. I think that means I will have to replace the fans. The power cables are hardwired to the fans and (as near as I can tell) unused wires have been clipped. Either that or they are tucked into some hidden nook or cranny. (This PC was built by a now defunct custom builder. I'm beginning to see why they went out of business.)

Any recommendations on fans? I assume I want fans with 4 wire power cables. These are front and back fans in a fairly unobstructed case so I think air flow is more important than static pressure. I'm limited to 120mm, and (of course) I'd like them to be inexpensive and quiet.

If you want "quiet" fans then the "Noctua" brand is what many choose. A four wire fan is a "PWM" type. I have three wire fans that came with my "BeQuiet" case and they are controllable and quiet. I use my PC for my recording studio and need a quiet PC.

I also use a quiet liquid cooler for the CPU.

OK. I got a Noctua NF-S12A PWM for pulling air in through a filter and a NF-F12A PWM for exhaust. My ne motherboard and CPU aren't due for another 4 or 5 days but I installed the fans ahead of time. And that may have been a mistake. On my old Gigabyte GA-X58A-UD3R motherboard there is one 4-pin fan header - the SYS-FAN2 header - so I hooked both fans to it with a Y connection that came with the fans. But I now see that the 4th pin in the header is a dummy; only 3 pins have connection. In other words this board does not have support for PWM case fans.

What happens to a PWM fan that receives no PWM control signal? Can this cause problems for the fan?

The old fans with their molex connection to the PSU were on all the time the PC was powered up. The new fans, wired to the SYS-FAN2 header, are sometimes on and sometimes off. I can't tell whether the board is using the old voltage level technique for controlling speed, just using voltage on/off for controlling the fan, or if the full voltage is always present but the fans are misbehaving.

The PC, when it's running at all, will have a very light load and is in a cool basement so I'm not particularly worried about its overheating. I'm more worried about damaging the fans.

Not sure but found this answer to a similar question on another forum:

he fourth pin is because PWM control needs four pins: two power lines, a sense line (fan speed), and a control line (PWM). You can control the fan speed through the UEFI ("BIOS"), Asus software, or other software with that function (I think SpeedFan does that, among others). The default M/B settings may control the fans adequately for you

CountMike said:

Actually pin assigment goes like this
1. Ground/negative
2. +12vdc
3. RPM sensing
4. RPM control thru PWM (Pulse Width Modulation).

3 pin fan's RPM can be controlled by varying voltage which makes weaker and air resistance slows it down.

4 pin fans have PWM lead for MB to send varying length and frequency to fan therefore speeding or slowing it down according to RPM sense to keep RPM steady to what it's set too.

3 and 4 pin fans can be used interchangeably with gain or loss of PWM feature. Depending on BIOS 4 pin fans can also be controlled by voltage.

My question (which you may have answered) was more about the fan rather than the controlling function. Will a fan designed for PWM control work correctly in a voltage control environment?

CountMike said:

Most modern MBs let you set a fan speed curve that regulates fan speed according to temperature of a sensor.

In a week I will start asking questions about a modern MB. For now I'm asking questions about a 9 year old Gigabyte X58A-UD3R.

I was recently given a custom computer with an ASUS mATX motherboard. The case it's in should have an ATX board as it has two case fans but the motherboard has only one Chassis Fan port/pins so only one fan was working. The hard drive took a hit on buildup of heat over time and is about gone. I used one of those Y cables to get power to the second fan, it was 4-wire but works fine for the 3-wire port and 2 fans. The plugs/sockets are indexed to be compatible for both types. The Y cable wouldn't have been necessary with a full-size ATX board as they frequently have ports for 2 or more chassis fans as would be necessary for the hard-core gamers or video editors.