Fan connection confusion, help pls!

Hello all,

I am doing my first build and have run into a problem. I am using the Antec 300 case, Antec EarthwattsEA 650, and the Gigabyte GA 790 seen here.

I've connected my cpu fan to the connector labeled CPU fan. I've connected the case fans with the 4 pin molex connectors. I had one connector coming from my PSU labled p9 that is a 4 pin connector, and I assume is the PSU fan (the manual doesn't have anything labeled). It is a 4 prong connector. There is only one 4 prong fan connector on the MOBO labeled sys_fan1. There are also 2 other 3 prong fan connectors on the MOBO (sys_fan2 and pwr_fan). Logic would tell me that I need to plug p9 into the 4 prong connector labled sys_fan, but I dont think the polarity of the different pins matches the way that they should on the motherboard. Does anybody have any idea what I need to do here?


Will Malcom
10 answers Last reply Best Answer
More about connection confusion
  1. Sounds like you are talking about the floppy connector.
  2. Best answer
    Do NOT plug that thing into your mobo fan connector!

    Here's how the four mobo FAN connectors go:
    1. CPU_FAN is ONLY for the CPU fan. Plug that fan in here, and nothing else. Within the BIOS you can configure how it deals with the CPU fan, but the typical default is that it will vary the CPU fan speed according to its settings for CPU temperatures. The temperature is actually measured by a sensor inside the CPU. The fan speed is monitored by one of the lines from it back to the mobo and shown to you in the BIOS screen.
    2. The PWR _FAN connector is ONLY for use with a special connector coming out of the PSU - and some don't have that line, so you connect NOTHING to this mobo point in that case. Read your PSU manual to see if it has that special line out. This does NOT control the PSU's fan speed. It only allows the BIOS to monitor that speed and display it. IF your PSU has a variable-speed fan, that is a function entirely within the PSU itself.
    3. SYS_FAN1 and 2 are BOTH available to connect case fans. The 4-pin one can accept either 4- or 3-pin case fan connections - it is designed to work with either fan type. On each of these there is a set of leads for Ground and fan power (variable for speed control), and one line feeding back the fan's speed signal. Similar to the CPU_FAN system, these SYS_FAN systems also are configured in the BIOS for control of temperature, BUT they are based on temperatures measured on the mobo, not within the CPU.

    If your case fans have only two wires coming out of them (typically red and black) to a male Molex 4-pin connector, they do not have a speed signal output line. But if they also have a third wire (typically yellow) that is the speed signal. Either way you can leave them connected to PSU Molex outputs to run them at full speed at all times. OR you can buy and install little fan speed modules that slip in between PSU Molex and fan, allowing you to set manually a slower speed. The third option would be to buy adapters that let you feed power to those fans from the SYS_FAN mobo connectors. The Ground and DC+ lines have to match up, but even without any speed signal they can work well, and you can let your mobo BIOS control those two fans' speeds for you. If there is no speed signal being fed back, you MIGHT have to tell the BIOS in the right spots to ignore those two fans' speed signals because there are none.

    So, what is that 4-pin connector from the PSU labeled P9? I don't know, youll have to look for info in its manual or on the maker's website, I guess.
  3. Best answer selected by WillMalcom.
  4. Thanks so much! I'll just be keeping everything the way I had it!
  5. Ok, here is a small update. I got everything slapped together, gave her some power and all of my fans are turning, all indicator lights are on, but I am getting an error on my monitor (no video cable input, check video cord =( ) oh well ... I will work this out! Thanks!
  6. that f pin P9 is an Auxiliary power connector no new motherboard needs them they haven't been used since the p3 days so just tuck that cable aside its nothing that you need.
  7. Thanks so much! Now I just have this stupid video signal check input cable error =(! Thanks!
  8. On your video problem, here are a few things to check.
    1. Are you using the built-in video of the mobo, or an add-on card in the PCI bus? IF your mobo has built-in video with a VGA output (or other) connector on the back panel, its BIOS probably is set by default to use that. So you should plug into that output connector, even if you also have an add-on card in a PCI slot. However, if you have NO built-in mobo video, connect to your video card's connector.
    2. Similarly, when you first start up your machine with no OS installed (you're just running the BIOS at this point), whichever video output device you have will default to a plain VGA signal output on its VGA connector, if there is one. So if you have both VGA and Digital video of some sort, try connecting each one to your monitor.
    3. Do you need to manually select which input your monitor is using? Some will auto-detect an incoming signal on its two or three input ports, but some simply allow you to select the input being displayed through buttons and menus on the monitor.
  9. Thanks for the response! Well, this MOBO has no integrated video. Yep, I've tried both video output ports, but they are both HDMI, no standard VGA. I've tried both inputs, so is it necessary that I even select the input manually? If I've tried both, shouldn't that cover my bases?

  10. If you've tried putting signals into both monitor ports and neither works, not much more to do there. I assume you have only one output connector on your video card, so there would be no switching to be done there. Only suggestion I have left is to try another monitor on your machine, and take your monitor to another machine and see what works. That may identify the malfunctioning unit.
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